JP2000016900A - Method for producing piezoelectric single crystal - Google Patents

Abstract

(57) [Problem] To provide a method capable of manufacturing a piezoelectric single crystal exhibiting an excellent electromechanical coupling coefficient while suppressing composition fluctuation. SOLUTION: A crucible (1) is heated by forming a local temperature gradient by a heater (6), and the crucible (1) is moved to produce a piezoelectric single crystal (3) comprising a composite perovskite oxide. In this case, the solid body of lead oxide and the sintered body (5) of the raw material constituting the piezoelectric single crystal are separated and accommodated in the crucible (1), and the solid body of lead oxide is melted and melted (4). ), The diameter of the crucible is r (mm),
Assuming that the height of the melt is h (mm), it is adjusted so that 3 ≦ h ≦ 200 and 0.03 ≦ h / r ≦ 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a piezoelectric single crystal used in an ultrasonic diagnostic apparatus and an ultrasonic flaw detector.

[0002]

2. Description of the Related Art An ultrasonic probe used in an ultrasonic diagnostic apparatus or an ultrasonic flaw detector irradiates an ultrasonic wave toward an object and receives reflected echoes from interfaces having different acoustic impedances in the object. Is used to image the internal state of the object. Ultrasonic probe
It is composed mainly of a piezoelectric element and has a thickness of several tens to several hundreds μm.
Array probes in which several tens to 200 rectangular piezoelectric elements are arranged have become mainstream. In order to improve the resolution of the ultrasonic probe, the number of piezoelectric elements tends to increase. Further, in order to increase the sensitivity and the bandwidth of the ultrasonic probe, improvement in the piezoelectric characteristics of the piezoelectric body is required. This is an electromechanical coupling coefficient of the piezoelectric body (k ₃₃ ', etc. k _t) is because the larger the sensitivity signal is obtained. Also,
If the dielectric constant of the piezoelectric body is large, matching with the transmission / reception circuit can be easily achieved, and loss due to stray capacitance of a cable or device can be reduced.

[0003] In response to these requirements, conventional titanium / zirconate lead (PZT) has been used as the piezoelectric material of the ultrasonic probe.
It is expected that a perovskite-type acid composite compound single crystal having a large electromechanical coupling coefficient will be used instead of the base ceramic (k ₃₃ ′ = about 70%). For example,
Pb which is a solid solution oxide single crystal of zinc / lead niobate Pb (Zn _1/3 Nb _2/3 ) O ₃ and lead titanate PbTiO ₃
[(Zn _1/3 Nb _2/3 ) _0.91 Ti _0.09 ] O ₃
It shows a large k ₃₃ ′ of 90%. When such a piezoelectric single crystal is used, it can be operated at a low frequency even if the piezoelectric element is made thin, which is advantageous for obtaining a high-sensitivity signal. When the piezoelectric element is thin, the cutting depth of the blade of the dicing machine can be reduced when processing into a strip, and the thin blade can be cut vertically, so that the production yield can be improved. Moreover, an ultrasonic probe with reduced side lobes can be provided. Further, since such a piezoelectric single crystal has a relative dielectric constant equal to or higher than that of a conventional PZT-based piezoelectric ceramic, matching with a transmission / reception circuit is good, and loss due to stray capacitance of a cable or device can be reduced. . Due to these factors, Pb [(Zn _1/3 Nb _2/3 ) _0.91 T
In the ultrasonic probe having a piezoelectric element using the i _0.09] O ₃ piezoelectric single crystal, as compared with those using the conventional PZT piezoelectric ceramics, or 6dB greater sensitivity signal is obtained. For this reason, a high-resolution B-mode image can be obtained up to a deep part of the body, and small lesions and voids can be clearly observed.

A piezoelectric body used for a piezoelectric element of an ultrasonic probe can be obtained in the form of a plate having a size of 10 mm square or more. When this is processed into an array, the piezoelectric characteristics and dielectric characteristics of each piezoelectric element are uniform. Is required.

Pb [(Zn _1/3 Nb _2/3 ) _0.91 T
A piezoelectric single crystal composed of a perovskite-type composite oxide such as i _0.09 ] O ₃ has a size of at least 10 mm square, which is a practically necessary level, by a method of growing from a solution such as a flux method or a Bridgman method. A single crystal can be grown. However, when trying to grow a single crystal having a size exceeding 10 mm square, a pyrochlore type single crystal (Pb ₃₎ having a large Nb ₂ O ₅ component ratio and a poor piezoelectric characteristic together with a piezoelectric single crystal composed of a perovskite-type composite oxide.
Nb ₄ O ₁₃ ) easily grows. This Nb ₂ O ₅
With the exhaustion of, the composition of the perovskite-type composite oxide fluctuates, and its piezoelectric and dielectric properties vary. As a result, the production yield of the piezoelectric vibrator processed into a strip shape is reduced, the sensitivity of the ultrasonic probe is reduced, and the band is deteriorated.

[0006] For example, 40 m grown by the flux method
Among ultrasonic probes using a piezoelectric element cut out from a single crystal having a size of about m square, there are cases where a signal level is low and a high-resolution image cannot be obtained. Examination of the piezoelectric element constituting the low-sensitivity ultrasonic probe shows that the value of the electromechanical coupling coefficient k ₃₃ ′ is lower than that of the other elements. further,
It has been found that a piezoelectric element that can obtain only a very low signal level has a composition deviating from a target piezoelectric single crystal composition and does not exhibit an original excellent electromechanical coupling coefficient. This is considered to be because the components segregated during the growth of the single crystal.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of producing a piezoelectric single crystal exhibiting an excellent electromechanical coupling coefficient while suppressing composition fluctuation.

[0008]

According to the method of manufacturing a piezoelectric single crystal of the present invention, a raw material containing lead oxide, niobium oxide and titanium oxide is contained in a crucible, and a local temperature gradient is formed by a heating source. Heating the crucible and moving the crucible to produce a piezoelectric single crystal of a composite perovskite oxide, a solid body of lead oxide and a sintered body of the raw material constituting the piezoelectric single crystal in the crucible When the melt is formed by melting and separating the solid body of the lead oxide, the diameter of the crucible is r (mm), and the height of the melt is h (m).
m), 3 ≦ h ≦ 200 and 0.03 ≦ h / r ≦
It is characterized in that it is adjusted to be in the range of 10.

[0009] In the method of the present invention, when the maximum temperature of the crucible during crystal growth T _M, the temperature of the crucible at a position crucible is separated from the position showing the highest temperature just diameter r of the crucible and T _R, the crucible Temperature distribution is 1050 ℃ ≦
T _M ≦ 1250 ° C. and 50 ° C. ≦ T _M −T _R ≦ 500 ° C.
It is preferable to set so as to fall within the range. Further, it is preferable to use a crucible having a multi-layer structure and formed of two or more kinds of materials.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The piezoelectric single crystal composed of a complex perovskite oxide, which is an object of the present invention, includes a complex oxide containing a divalent or trivalent metal element. _{Specifically, Pb [(Zn 1/3 Nb 2/3} ) 1-x Ti x] O
₃ (0.05 ≦ x ≦ 0.20), Pb [(Mg _1/3 Nb
_2/3 ) _1-x Ti _x ] O ₃ (0.20 ≦ x ≦ 0.40),
_{Pb [(Ni 1/3 Nb 2/3)} 1-x Ti x] O 3 (0.3
0 ≦ x ≦ 0.50), Pb [(Co _1/3 Nb _2/3 ) _1-x
Ti _x ] O ₃ (0.10 ≦ x ≦ 0.30), Pb [(A
_{1/3 Nb 2/3) 1-x Ti} x] O 3 (A is Sc, In, F
e, Y, and at least one element selected from the group consisting of rare earth elements, 0.30 ≦ x ≦ 0.50). Also included are composite oxides of lead tantalate titanate in which a part of Nb of these composite oxides is substituted by Ta.
Further, a composite oxide or the like obtained by combining them is also included.

In the present invention, a solid body of lead oxide and a sintered body of a raw material constituting a piezoelectric single crystal are separately accommodated in a crucible. The sintered body of the raw material constituting the piezoelectric single crystal is
The raw materials are mixed so as to have almost the same composition as the piezoelectric single crystal as exemplified above, solidified, and then fired. In addition, solid body (pellet) of lead oxide (PbO)
Is used as a flux.

In the present invention, a crucible is heated by forming a local temperature gradient by a heating source in a tubular electric furnace or the like,
A so-called Bridgman method is used in which the crucible is moved from top to bottom to grow a piezoelectric single crystal from the bottom of the crucible.
In the crucible, PbO pellets and a piezoelectric single crystal raw material sintered body are separated and accommodated in this order from below. Note that a seed crystal of a piezoelectric single crystal may be accommodated below the PbO pellet.

When the crucible is heated by a heating source, 900
Above ° C, PbO first melts. The height of this melt is P
The weight of the bO pellet is W, and the density of the PbO melt is d (~
9.5 g / cm ³ ), h = 4 W / (πr ² d)
It is. Further, when the temperature exceeds 1050 ° C., a part of the raw material sintered body starts to be melted, melts into the PbO melt and saturates. At this time, the height of the melt in the crucible is initially Pb.
It becomes higher than the height of the melt containing only O. When the crucible is cooled down, the piezoelectric single crystal starts to grow from the bottom of the crucible. When the crucible is slowly moved under a temperature gradient, the raw material sintered body is melted and supplied continuously according to the growth of the piezoelectric single crystal. A body single crystal can be produced.

In the present invention, the diameter (inner diameter) of the crucible is set to r (mm) in order to melt the raw material sintered body as described above and to continuously supply the material to the piezoelectric single crystal growth site. Is adjusted to be in the range of 3 ≦ h ≦ 200 and 0.03 ≦ h / r ≦ 10, where h is the height (mm).

H is less than 3 mm or h / r ratio is 0.0
If it is less than 3, cracks and inclusions are liable to occur in the piezoelectric single crystal, and the necessary 1
It becomes impossible to form a piezoelectric element of 0 mm square or more. h is 20
If it exceeds 0 mm or the h / r ratio exceeds 10,
The growth site of the piezoelectric single crystal and the upper raw material sintered body are too far apart to supply a raw material having a desired composition, and pyrochlore single crystal Pb ₃ (Nb, Ta) ₄ O ₁₃ is generated. The composition fluctuation of the perovskite-type single crystal increases.
As a result, it becomes difficult to obtain a piezoelectric single crystal of 10 mm square or more. The h / r ratio is 0.2 to
More preferably, it is in the range of 1.5.

By using the method of the present invention, the generation of a pyrochlore single crystal can be suppressed, and the generation of a pyrochlore single crystal can be suppressed without changing the composition.
A perovskite-type composite oxide piezoelectric single crystal of 0 mm square or more can be grown. For this reason, even if a single-crystal plate cut out from the obtained piezoelectric single crystal is array-processed to produce a strip-shaped piezoelectric vibrator, variations in piezoelectric characteristics and dielectric characteristics can be reduced. Therefore, it is possible to realize an ultrasonic probe having a higher sensitivity and a wider band than an ultrasonic probe using conventional piezoelectric ceramics.

In the present invention, in order to satisfy the above condition relating to the height of the melt, the maximum temperature of the crucible is set to T _M , and the temperature of the crucible at a position separated by a diameter r of the crucible from the position where the crucible shows the maximum temperature. when the the T _R, the temperature distribution of the _{crucible, 1050 ℃ ≦ T M ≦ 1250} ℃, and 5
It is preferable to set the local temperature gradient such that 0 ℃ ≦ T _M -T range _R ≦ 500 ° C..

When T _M is less than 1050 ° C., the melting of the raw material sintered body becomes insufficient and the number of nuclei increases, so that 10 m
It becomes difficult to obtain a piezoelectric single crystal having an m square or more. T _M is 1
If the temperature exceeds 250 ° C., a pyrochlore type single crystal having poor piezoelectric properties is likely to be formed, and the composition fluctuation inside the perovskite type single crystal becomes large.

If T _M -T _R (= ΔT) is less than 50 ° C., nuclei are generated too much, making it difficult to obtain a piezoelectric single crystal of 10 mm square or more. When ΔT exceeds 500 ° C., the temperature gradient is too steep, so that cracks and inclusions are apt to occur in the piezoelectric single crystal, and it becomes impossible to form a piezoelectric element having a size of 10 mm square or more required for an ultrasonic probe.

In the process of growing a single crystal, it is sufficient that a PbO melt containing a single crystal raw material at a saturated concentration is present above the growth site of the piezoelectric single crystal in the crucible.
Instead of the bO solid (pellet), the ratio (K = C _S / C _F ) of the amount (C _S ) of the component constituting the single crystal and the amount (C _F ) of PbO to be the flux is 4 in molar ratio. The same effects as in the case of using a PbO solid can be obtained by using the following solid.

In the present invention, a crucible made of a noble metal such as platinum can be used, but the structure of the crucible is not particularly limited. For example, a crucible having a multiple structure and formed of two or more materials can be suitably used. In particular, a crucible having an inner wall made of a noble metal or an alloy thereof and an outer wall made of a refractory is preferable.
Note that a multiple crucible formed of two or more types of metals or a multiple crucible formed of two or more types of refractories may be used. In such a multiple crucible, the outer wall or the intermediate layer has an effect of reducing the difference in thermal expansion between the inner wall and the single crystal, and an effect of suppressing the generation of pinholes due to corrosion of the inner wall.

Examples of the noble metal include Pt, Ir, Rh and the like. The alloy is a Pt-Rh alloy with Rh / P
The weight ratio of t is from 0.01 to 1, more preferably from 0.1 to 1.
0.4, and a Pt-Ir alloy having a weight ratio of Ir / Pt of 0.01 to 1, more preferably 0.2 to 0.8. Further, reinforced platinum in which Y ₂ O ₃ or ZrO ₂ is dispersed may be used. Other refractories include oxides such as high-purity alumina and magnesia, and nitrides such as aluminum nitride.

More specific structures of the multiple crucible include the following. For example, the inner wall is Pt,
The outer wall is made of alumina or magnesia; the inner wall is made of Pt, the intermediate layer is Rh, the outer wall is made of reinforced platinum in which ZrO ₂ is dispersed; the inner wall is made of Pt, the intermediate layer is AlN, the outer wall is made of alumina, and the like. . Further, a heat insulating material such as glass wool or bubble alumina may be inserted as the intermediate layer.

The shape of the crucible is not particularly limited. Generally, a cylindrical shape is often used, but a cylindrical shape such as a rectangular parallelepiped or a cone may be used. Further, the bottom of the cylinder is generally pointed, but may be flat. A pipe for putting a seed crystal for growing a crystal or a rod for cooling may be provided at the bottom of the crucible. The seed portion and the cooling rod may have a single-layer structure or a multi-layer structure. However, the seed portion is preferably formed only of a metal having a high thermal conductivity.

The thickness of the metal layer on the inner wall of the crucible is not particularly limited. For example, in a cylindrical crucible having a diameter of 40 mm, the thickness is preferably about 0.1 to 0.3 mm. The thicker the refractory of the outer wall of the crucible is, the more advantageous it is in strength. However, if the thickness is too large, it is difficult to break the refractory and take out the crystal. Generally, 0.3 to 30
mm, more preferably 1 to 10 mm.

It is desirable to cover the crucible with a lid. The lid is preferably made of the same material as the crucible, but may be made of platinum alone. The lid may be fixed by welding, fixed by weight, or fixed by mechanical bending.

The crucible may be hung from above or supported from below, and it is preferable that the crucible can be easily moved. A tool for holding the crucible is not particularly limited, and a heat-resistant product such as a heat-resistant brick or heat-resistant glass, a Pt-Rh alloy, or the like may be used.

The moving direction of the crucible is not particularly limited. Usually a top-to-bottom movement, but from bottom to top, horizontally,
Any of a diagonally downward direction, a diagonally upward direction, and the like may be used, or these may be combined. Crucible moving speed is 0.05 ~
5 mm / h, more preferably 0.2 to 1 mm / h.
It is desirable that the moving speed of the crucible be constant, but the speed may be changed during the growing. The crucible may be rotated or vibrated. The heating area is not particularly limited,
An electric furnace that can be controlled by electricity is desirably used, and desirably a size that can accommodate a crucible that can grow a single crystal having a sufficient size. Since the crucible only needs to pass through the heating area, the crucible does not necessarily need to move, and the electric furnace itself may move, or the position of the high-temperature portion may be moved by controlling the current of the heating element. The heating element is not limited, but alloys, SiC, MoSi ₂ , LaCr capable of realizing a high temperature of 1000 ° C. or higher.
Generally, an O ₃ -based heater is used. Although the above description has been made on the assumption that the crystal is grown in a normal pressure atmosphere, the atmosphere is not particularly limited. An oxidizing gas such as oxygen or air may flow in, or the pressure may be increased to normal pressure (1 atm) or more.

[0030]

Embodiments of the present invention will be described below.

Example 1 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed so that the molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ was 91: 9. These raw material powders were mixed well, and a 5% solution of polyvinyl alcohol as a binder was added and mixed well. This mixed powder is hardened by an isostatic press and placed in an electric furnace for 110 minutes.
Baking at 0 ° C for 4 hours, outer diameter 49mm x length 200mm
Was obtained. The PbO powder was solidified by an isostatic press to produce PbO pellets having an outer diameter of 49 mm and a length of 50 mm.

As shown in FIG. 1, a PbO pellet and a raw material sintered body 5 are accommodated from below in a cylindrical platinum crucible 1 having an inner diameter of 50 mm and a length of 300 mm having a cooling rod 2 at the bottom, and the crucible 1 is sealed. Was. This crucible 1 was suspended at the center of a tubular electric furnace. With the heater 6 capable of local heating, the temperature is raised to the maximum temperature of 1200 ° C. in 6 hours, and PbO
The pellet was completely melted and a part of the raw material sintered body 5 was melted to form a melt 4. The maximum temperature of the electric furnace is 12
While maintaining the temperature at 00 ° C., the crucible 1 was lowered at a rate of 0.3 mm / h by about 600 mm while rotating at 10 rpm, and then the electric furnace was gradually cooled to room temperature to grow the piezoelectric single crystal 3.

When the temperature gradient of the crucible in the electric furnace was examined in advance during the growth, the maximum temperature of the crucible was 1200 ° C., and the diameter (50 mm) of the crucible was shifted upward or downward from that position.
mm), the temperature of the crucible at a position separated by the same distance was 1050 ° C. on the upper side and 1000 ° C. on the lower side. When the height (h) of the melt in the crucible 1 was examined under these temperature conditions, it was found that h = 40 mm. Further, the height (h ′) of the melt after holding at 1200 ° C. for 6 hours was as high as h ′ = 50 mm because the raw material sintered body 4 was partially melted. Therefore, h / r is 0.8 to 1.0.

After the growth is completed, the crucible is removed and the contents are taken out. The diameter is 50 mm × 190 m from the bottom of the crucible.
An m-length crystal was growing. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. The growth orientation was <100> direction. When the composition of this single crystal was analyzed by the ICP method, Pb [(Zn
_1/3 Nb _2/3 ) _1-x Ti _x ] O ₃ , x = 0.091 ±
It was found to be within 0.001. From the temperature change of the dielectric constant of the piezoelectric single crystal, the Curie temperature T _c = 185
° C. ± 3 ° C. Within, it was found transition temperature T _x = 65 ° C. is within ± 2 ° C.. No pyrochlore single crystal was generated.

From the Laue photograph of the piezoelectric single crystal, {100}
The orientation of the plane was determined, and a piezoelectric single crystal plate having a thickness of 0.4 mm, a size of 10 mm × 20 mm square was cut out with a diamond blade. Both sides of this piezoelectric single crystal plate are # 2
Polished and washed to a thickness of 0.26 mm with 000 carborundum abrasive grains. Thereafter, a Ti / Au electrode (Ti thickness = 100 nm, Au
(Thickness = 1000 nm) to obtain a piezoelectric element. This piezoelectric element was immersed in an oil bath containing silicone oil, the silicone oil was heated to 250 ° C., and an electric field of 1 kV / mm was applied by electrodes on both sides to hold the piezoelectric element for 30 minutes. While the electric field is applied, raise the temperature of the silicone oil to 1
The temperature was lowered to room temperature at a rate of ° C./min, and the piezoelectric element was subjected to electric field cooling. The electric field was released, and the piezoelectric element was taken out of the silicone oil and washed. The piezoelectric single crystal plate thus subjected to the polarization treatment is subjected to dicing with a dicer to a width of 0.15 mm × length 1
It was processed into a rectangular piezoelectric vibrator of 0 mm × 0.26 mm in thickness. The resonance and anti-resonance frequencies of 50 piezoelectric vibrators were measured from the frequency characteristics of admittance,
From these values, the electromechanical coupling coefficient k ₃₃ ′ was determined. As a result, it was found that the value of k ₃₃ ′ of the piezoelectric vibrator was as large as 90% to 91%, and the variation was small.

Another single crystal plate having a {100} plane and a thickness of 0.26 mm and a size of 15 mm × 20 mm square was processed from the piezoelectric single crystal. By sputtering, a Ti / Au electrode (Ti thickness: 50 n) is formed on both upper and lower surfaces and side surfaces of the single crystal plate.
m, Au thickness: 500 nm). After the electrode formed on the side surface of the single crystal plate and a part of the electrode formed on the surface opposite to the ultrasonic wave receiving surface were removed by selective etching, polarization was performed in the same manner as described above. After forming an acoustic matching layer on the ultrasonic receiving surface of the single crystal plate, it was adhered on the backing material. A single crystal plate was cut from the acoustic matching layer using a diamond blade having a thickness of 0.03 mm, cut into strips at a pitch of 0.19 mm, and separated from each other having a first electrode and a second electrode on a backing material. One hundred piezoelectric vibrators were formed. An acoustic lens was formed on the acoustic matching layer. The conductive layer of the flexible printed wiring board was connected to each first electrode by soldering, and the ground electrode plate was connected to the second electrode by soldering. A plurality of cables each having a length of 2 m and 110 pF / m were connected to the flexible printed wiring board and the ground electrode plate, thereby manufacturing an array type ultrasonic probe. Using the obtained array type ultrasonic probe, the reflection echo was measured by the pulse echo method. As a result, echoes having a center frequency of 2.5 MHz were obtained in all the elements.

Example 2 Raw material powders of PbO, MgO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed such that the molar ratio between (Mg _1/3 Nb _2/3 ) O ₃ and lead titanate PbTiO ₃ was 70:30.
These raw material powders were mixed well, and a 5% solution of polyvinyl alcohol as a binder was added and mixed well.
This mixed powder was hardened by a hydrostatic press and placed in an electric furnace to obtain 11
Bake at 00 ° C for 6 hours, outer diameter 49mm x length 250m
m of the raw material sintered body was obtained. The PbO powder was solidified by an isostatic press to produce PbO pellets having an outer diameter of 49 mm and a length of 40 mm.

As shown in FIG. 1, a PbO pellet and a raw material sintered body 5 are accommodated from below in a cylindrical platinum crucible 1 having an inner diameter of 50 mm and a length of 350 mm having a cooling rod 2 at the bottom, and the crucible 1 is sealed. Was. This crucible 1 was suspended at the center of a tubular electric furnace. With the heater 6 capable of local heating, the temperature is raised to the maximum temperature of 1220 ° C. in 10 hours, and Pb
The O pellets were completely melted and a part of the raw material sintered body 5 was melted to form a melt 4. Set the maximum temperature of the electric furnace to 1
While maintaining the temperature at 220 ° C., the crucible 1 was lowered at a rate of 0.4 mm / h by about 600 mm while rotating at 5 rpm, and then the electric furnace was gradually cooled to room temperature to grow crystals.

When the temperature gradient of the crucible in the electric furnace was examined in advance during the growth, the maximum temperature of the crucible was 1220 ° C.
mm), the temperature of the crucible at the same distance from the crucible was 1070 ° C. on the upper side and 1020 ° C. on the lower side. When the height (h) of the melt in the crucible 1 was examined under these temperature conditions, it was found that h = 30 mm. The height (h ′) of the melt after holding at 1220 ° C. for 10 hours is h ′ = 40 mm
Met. Therefore, h / r is 0.6 to 0.8.

After the growing, the crucible was removed and the contents were taken out. The diameter of the crucible was 50 mm × 210 m from the bottom side.
An m-length crystal was growing. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. The composition of the single crystal was analyzed by the ICP method, with _{Pb [(Mg 1/3 Nb 2/3)} 1-x Ti x] O 3,
It was found that x was within 0.315 ± 0.005. From the temperature change of the dielectric constant of the piezoelectric single crystal, the Curie temperature T _c = 155 ° C. ± 5 ° C. and the transition temperature T _x = 95
It was found that the temperature was within ± 3 ° C. No pyrochlore single crystal was generated.

From the Laue photograph of the piezoelectric single crystal, {100}
The orientation of the plane was determined, and a piezoelectric single crystal plate having a thickness of 0.4 mm, a size of 10 mm × 20 mm square was cut out with a diamond blade. Both sides of this piezoelectric single crystal plate are # 2
Polished and washed to a thickness of 0.26 mm with 000 carborundum abrasive grains. Thereafter, a Ti / Au electrode (Ti thickness = 100 nm, Au
(Thickness = 1000 nm) to obtain a piezoelectric element. This piezoelectric element was processed into a strip-shaped piezoelectric vibrator by performing polarization treatment and dicing in the same manner as in Example 1. The resonance / anti-resonance frequency was measured from the frequency characteristics of the admittance, and the electromechanical coupling coefficient k ₃₃ ′ was obtained from these values. As a result, it was found that the value of k ₃₃ ′ of the piezoelectric vibrator was as large as 85% to 86%, and the variation was small.

In the same manner as in Example 1, an array type ultrasonic probe was manufactured using another single crystal plate processed from a piezoelectric single crystal. Using the obtained array type ultrasonic probe, the reflection echo was measured by the pulse echo method. As a result, echoes having a center frequency of 2.5 MHz were obtained in all the elements.

Example 3 Raw material powders of PbO, MgO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed such that the molar ratio between (Mg _1/3 Nb _2/3 ) O ₃ and lead titanate PbTiO ₃ was 70:30.
These raw material powders were mixed well, and a 5% solution of polyvinyl alcohol as a binder was added and mixed well.
This mixed powder was hardened by a hydrostatic press and placed in an electric furnace to obtain 11
Baking at 00 ° C for 6 hours, outer diameter 49mm x length 220m
m of the raw material sintered body was obtained. The PbO powder was solidified by an isostatic press to produce PbO pellets having an outer diameter of 49 mm and a length of 50 mm.

As shown in FIG. 2, inner diameter 50 mm × length 3
An inner wall 11 made of platinum having a thickness of 00 mm × 0.2 mm, an outer wall 12 made of alumina porcelain having a thickness of 3 mm, and a cooling rod made of platinum having a thickness of 3 mm and a length of 100 mm provided at the bottom center of the inner wall 11. Crucible 10 having 13 was used in place of crucible 1 of FIG. The PbO pellets and the raw material sintered body 5 were accommodated in the crucible 10 from below, and the crucible 10 was sealed. This crucible 10 was hung at the center of a tubular electric furnace. The temperature was raised to the maximum temperature of 1220 ° C. in 10 hours by the heater 6 capable of local heating, and the PbO pellets were completely melted and a part of the raw material sintered body 5 was melted to form a melt 4. 0.4 mm while rotating the crucible 1 at 5 rpm while maintaining the maximum temperature of the electric furnace at 1220 ° C.
After lowering by about 600 mm at a descent rate of / h, the electric furnace was gradually cooled to room temperature to grow crystals. When the temperature gradient of the crucible in the electric furnace was examined in advance during the growth, the maximum temperature of the crucible was 1220 ° C., and the crucible was located at the same distance as the diameter (50 mm) of the crucible upward or downward from that position. The temperature of the upper side is 1040 ° C and the lower side is 1040 ° C.
00 ° C. When the height (h) of the melt in the crucible 1 was examined under these temperature conditions, it was found that h = 35 mm. The height (h ′) of the melt after holding at 1220 ° C. for 10 hours was h ′ = 60 mm. Therefore, h
/ R is 0.7 to 1.2.

After completion of the growth, the crucible was removed and the contents were taken out. The diameter of the crucible was 50 mm × 190 m from the bottom side.
An m-length crystal was growing. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. The composition of the single crystal was analyzed by the ICP method, with _{Pb [(Mg 1/3 Nb 2/3)} 1-x Ti x] O 3,
It was found that x was within 0.31 ± 0.01. From the temperature change of the dielectric constant of the piezoelectric single crystal, the Curie temperature T _c = 155 ° C. ± 7 ° C. and the transition temperature T _x = 95 ° C. ± 5 ° C.
It was found to be within ° C. No pyrochlore single crystal was generated.

From the Laue photograph of the piezoelectric single crystal, {100}
The orientation of the plane was determined, and a piezoelectric single crystal plate having a thickness of 0.4 mm, a size of 10 mm × 20 mm square was cut out with a diamond blade. Both sides of this piezoelectric single crystal plate are # 2
Polished to a thickness of 0.24 mm with 000 carborundum abrasives and washed. Thereafter, a Ti / Au electrode (Ti thickness = 100 nm, Au
(Thickness = 1000 nm) to obtain a piezoelectric element. This piezoelectric element was processed into a strip-shaped piezoelectric vibrator by performing polarization treatment and dicing in the same manner as in Example 1. The resonance / anti-resonance frequency was measured from the frequency characteristics of the admittance, and the electromechanical coupling coefficient k ₃₃ ′ was obtained from these values. As a result, it was found that the value of k ₃₃ ′ of the piezoelectric vibrator was as large as 85% to 87% and the variation was small.

In the same manner as in Example 1, an array type ultrasonic probe was manufactured using another single crystal plate processed from a piezoelectric single crystal. Using the obtained array type ultrasonic probe, the reflection echo was measured by the pulse echo method. As a result, echoes having a center frequency of 2.5 MHz were obtained in all the elements.

Example 4 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ is 91: 9, that is, Pb [(Z
The raw material powder was weighed so as to have a composition ratio of n _1/3 Nb _2/3 ) _0.91 Ti _0.09 ] O ₃ . Mix these raw material powders well,
Further, a 5% solution of polyvinyl alcohol as a binder is added and mixed well, and pellets (PZ) are pressed with an isostatic press.
(N-PT91 / 9 pellets). 500 g of the pellets were fired at 1100 ° C. for 4 hours to obtain a raw material sintered body.

As shown in FIG. 2, inner diameter 40 mm × length 2
An inner wall 11 made of platinum having a size of 00 mm × 0.2 mm, an outer wall 12 made of alumina porcelain having a thickness of 3 mm, and a cooling rod 13 made of platinum having a thickness of 5 mm and a length of 100 mm provided at the bottom center of the inner wall. Was prepared. This crucible 10 is filled with 350 g of PbO and a raw material sintered body,
It was passed through a tube furnace set at 1230 ° C. with a platinum lid. The moving speed was 0.5 mm / h. The time required for growing the single crystal was 20 days.

The crucible was broken with a diamond cutter and pliers, and the crystal was taken out. As a result, 420 g of a crystal having a diameter of 40 mm × a length of 30 mm was deposited. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. When this crystal was observed in detail,
No cracks or dislocations were observed.

The double crucible used in this embodiment is 0.2 m
Since the inner wall made of platinum having a thickness of m is reinforced by the outer wall made of alumina, it is possible to prevent the occurrence of pinholes on the inner wall being grown. Moreover, since alumina has a coefficient of thermal expansion intermediate between platinum and a crystal, the difference in the coefficient of thermal expansion can be reduced to prevent crystal cracking and dislocation.

Example 5 In the same manner as in Example 4, 600 g of PZN-PT91 /
Nine pellets were prepared and fired at 1100 ° C. for 4 hours to obtain a raw material sintered body. An inner wall made of platinum having an inner diameter of 40 mm x a length of 200 mm x a thickness of 0.2 mm, an intermediate layer made of MgO having a thickness of 1 mm, and an outer wall made of alumina porcelain having a thickness of 1 mm;
Thickness 3 mm x length 100 provided at the bottom center of the inner wall
A triple crucible having a mm cooling rod made of platinum was prepared.
This crucible was filled with 300 g of PbO and a raw material sintered body, passed through a tubular furnace set at 1200 ° C. with a platinum lid. The moving speed was 0.2 mm / h. The time required for growing the single crystal was 50 days.

The crucible was broken with a diamond cutter and pliers, and the crystals were taken out. As a result, 530 g of crystals having a diameter of 40 mm and a length of 25 mm were deposited. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. When this crystal was observed in detail,
No cracks or dislocations were observed.

In the triple crucible used in this embodiment, since the MgO intermediate layer exists between the inner wall made of platinum and the outer wall of alumina, even if a pinhole is generated in the inner wall, the outer wall is not damaged. This is because MgO hardly reacts with PbO. If there is no MgO intermediate layer, when pinholes are generated on the inner wall, not only is alumina mixed into the raw material to break the perovskite single crystal to generate a pyrochlore single crystal, but also the alumina reacts with PbO to reach the outer wall. It may be damaged.

Example 6 In the same manner as in Example 4, 440 g of PZN-PT91 /
Nine pellets were prepared and fired at 1100 ° C. for 4 hours to obtain a raw material sintered body. An inner wall made of platinum having an inner diameter of 40 mm, a length of 200 mm and a thickness of 0.2 mm, and a platinum (Pt) / rhodium (Rh) having a thickness of 0.1 mm (Pt / Rh = 9 in atomic ratio)
/ 1), and a double crucible having a platinum cooling rod of 1 mm in thickness and 100 mm in length provided at the center of the bottom surface of the inner wall. This crucible was filled with 350 g of PbO and a raw material sintered body, passed through a tubular furnace set at 1200 ° C. with a platinum lid. The moving speed is 0.2mm /
h. The time required for growing the single crystal was 50 days.

The crucible was broken with a diamond cutter and pliers, and the crystal was taken out. As a result, 330 g of a crystal having a diameter of 40 mm × a length of 30 mm was deposited. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. When this crystal was observed in detail,
No cracks or dislocations were observed.

Since the double crucible used in this embodiment has a thin outer wall made of a high-strength platinum-rhodium alloy, the crystal can be prevented from cracking.

Example 7 In the same manner as in Example 4, 500 g of PZN-PT95 /
Five pellets were prepared and fired at 1100 ° C. for 4 hours to obtain a raw material sintered body. An inner wall made of platinum having an inner diameter of 40 mm, a length of 200 mm, and a thickness of 0.2 mm, an outer wall made of magnesia having a thickness of 1 mm, and a thickness 3 provided at the bottom center of the inner wall.
A double crucible having a cooling rod made of platinum and having a length of 100 mm and a length of 100 mm was prepared. This crucible was filled with 330 g of PbO and a raw material sintered body, passed through a tubular furnace set at 1130 ° C. with a platinum lid. The moving speed is 0.2mm / h
And The time required for growing the single crystal was 50 days.

When the crucible was broken with a diamond cutter and pliers and the crystal was taken out, 400 g of a crystal having a diameter of 40 mm × a length of 30 mm was deposited. When this crystal was examined by a Laue photograph and an X-ray diffraction method, it was found that it was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature. When this crystal was observed in detail,
No cracks or dislocations were observed.

The double crucible used in this embodiment is the same as that of the fourth embodiment.
The type of refractory that is the outer wall is different from that of Example 4
Although the alumina constituting the outer wall is advantageous in strength,
Since it reacts easily with PbO, there is concern about long-term use. On the other hand, magnesia constituting the outer wall in the present embodiment is inferior to alumina in strength, but hardly reacts with PbO, so that it can be used for a long time.

Comparative Example 1 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed so that the molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ was 91: 9. These raw material powders were mixed well, and a 5% solution of polyvinyl alcohol as a binder was added and mixed well. This mixed powder is hardened by an isostatic press and placed in an electric furnace for 110 minutes.
Fired at 0 ° C for 4 hours, outer diameter 29mm x length 150mm
Was obtained. The PbO powder was solidified by an isostatic press to produce PbO pellets having an outer diameter of 29 mm and a length of 300 mm.

As in FIG. 1, a PbO pellet and a raw material sintered body 5 are accommodated from below in a cylindrical platinum crucible 1 having an inner diameter of 30 mm × length of 500 mm having a cooling rod 2 at the bottom.
The crucible 1 was sealed. This crucible 1 was suspended at the center of a tubular electric furnace. By heater 6 which can do local heating,
The temperature was raised to the maximum temperature of 1200 ° C. in 6 hours, and the PbO pellets were completely melted and a part of the raw material sintered body 5 was melted to form a melt 4. Maximum temperature of electric furnace is 1200
The crucible 1 was lowered at about 0.3 mm / h at a rate of about 600 mm while rotating at 10 rpm while maintaining the temperature, and then the electric furnace was gradually cooled to room temperature to grow crystals.

When the temperature gradient of the crucible in the electric furnace was examined in advance during the growth, the maximum temperature of the crucible was 1200 ° C., and the diameter of the crucible was raised or lowered from that position (50 ° C.).
mm), the temperature of the crucible at a position separated by the same distance was 1050 ° C. on the upper side and 1000 ° C. on the lower side. When the height (h) of the melt in the crucible 1 was examined under these temperature conditions, it was found that h = 260 mm. The height (h ′) of the melt after holding at 1200 ° C. for 6 hours is h ′ = 300 mm
Met. Therefore, h / r is 8.7-10.

After the growth, the crucible was removed and the contents were taken out. The crucible was 20 mm in diameter × 20 mm from the bottom side of the crucible.
Long yellow-brown crystals and several red crystals having a size of 10 mm square were grown thereon. When these crystals were examined by Laue photograph and X-ray diffraction method, the yellowish brown crystal was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature, and the red crystal was a pyrochlore single crystal (Pb ₃ Nb ₄ O ₁₃ ). It turned out to be. When the composition of the perovskite-type piezoelectric single crystal was analyzed by the ICP method, Pb [(Zn _1/3
Nb _2/3 ) _1-x Ti _x ] O ₃ , where x = 0.089-0.
It was found that the variation was in the range of 107. From the temperature change of the dielectric constant of the piezoelectric single crystal, the Curie temperature T _c
= 170 to 200 ° C, and the transition temperature T _x = 45 to 110 ° C.

From the Laue photograph of the piezoelectric single crystal, {100}
The orientation of the plane was determined, and a piezoelectric single crystal plate having a thickness of 0.4 mm, a size of 10 mm × 20 mm square was cut out with a diamond blade. Both sides of this piezoelectric single crystal plate are # 2
Polished and washed to a thickness of 0.26 mm with 000 carborundum abrasive grains. Thereafter, a Ti / Au electrode (Ti thickness = 100 nm, Au
(Thickness = 1000 nm) to obtain a piezoelectric element. This piezoelectric element was immersed in an oil bath containing silicone oil, the silicone oil was heated to 250 ° C., and an electric field of 1 kV / mm was applied by electrodes on both sides to hold the piezoelectric element for 30 minutes. While the electric field is applied, raise the temperature of the silicone oil to 1
The temperature was lowered to room temperature at a rate of ° C./min, and the piezoelectric element was electric field cooled. The electric field was released, and the piezoelectric element was taken out of the silicone oil and washed. The piezoelectric single crystal plate thus subjected to the polarization treatment is subjected to dicing with a dicer to a width of 0.15 mm × length 1
It was processed into a rectangular piezoelectric vibrator of 0 mm × 0.26 mm in thickness. The resonance and anti-resonance frequencies of 50 piezoelectric vibrators were measured from the frequency characteristics of admittance,
From these values, the electromechanical coupling coefficient k ₃₃ ′ was determined. As a result, the value of k ₃₃ ′ of the piezoelectric vibrator varied greatly from 75% to 91%.

Comparative Example 2 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed so that the molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ was 91: 9. PbO was weighed such that the molar ratio between the single crystal raw material powder and the flux (PbO) was 30/70. These are mixed well, and the mixed powder is hardened by an isostatic press, and the outer diameter is 60 m.
A pellet having a size of mx 80 mm in length was prepared.

The above pellets were placed in a cylindrical platinum crucible having an inner diameter of 70 mm × length of 100 mm, and the crucible was sealed. This crucible was hung at the center of a tubular electric furnace.
The temperature was raised to a maximum temperature of 1230 ° C. in 12.5 hours by a heater capable of locally heating, and gradually cooled to 850 ° C. at a cooling rate of 0.5 ° C./h, followed by furnace cooling to room temperature. Thus, the crystal was grown by the ordinary flux method.

When the melt held at 1230 ° C. was examined in advance, the single crystal raw material powder was completely melted.

After the completion of the growth, the crucible was removed and the contents were taken out. Two light yellow-brown crystals of about 30 mm square and three red crystals of 20 mm square were placed around the bottom of the crucible. They were growing together as a lump. When these crystals were examined by Laue photograph and X-ray diffraction method, it was found that the pale yellowish brown crystal was a piezoelectric single crystal having a rhombohedral perovskite structure at room temperature, and the red crystal was a pyrochlore single crystal. When the composition of the perovskite-type piezoelectric single crystal was analyzed by the ICP method, Pb [(Z
In _{n 1/3 Nb 2/3) 1-x} Ti x] O 3, x = 0.93~
It was found that the variation was in the range of 0.115. From the temperature change of the dielectric constant of the piezoelectric single crystal, the Curie temperature T _c = 170 to 190 ° C. and the transition temperature T _x = 40 to 110
It was found that the temperature varied in the range of ° C.

From the Laue photograph of the piezoelectric single crystal, {100}
The orientation of the surface was determined, cut out with a diamond blade, polished, finished to a thickness of 0.26 mm, and washed. Sputtering Ti / Au on piezoelectric single crystal plate
Electrode (Ti thickness = 100 nm, Au thickness = 1000 n)
m) was formed to obtain a piezoelectric element. This piezoelectric element is immersed in an oil bath containing silicone oil, the silicone oil is heated to 250 ° C., and 0.3 k
An electric field of V / mm was applied and held for 30 minutes. With the electric field applied, the temperature of the silicone oil was lowered to room temperature at a rate of 1 ° C./min, and the piezoelectric element was subjected to electric field cooling. The electric field was released, and the piezoelectric element was taken out of the silicone oil and washed. The piezoelectric single crystal plate thus subjected to the polarization treatment is
It was processed into a rectangular piezoelectric vibrator having a width of 0.15 mm, a length of 10 mm and a thickness of 0.26 mm by a dicer. The resonance / anti-resonance frequencies of the 20 piezoelectric vibrators were measured from the frequency characteristics of admittance, and the electromechanical coupling coefficient k ₃₃ ′ was determined from these values. As a result, it was found that the value of k ₃₃ ′ of the piezoelectric vibrator was as small as 75% to 83%, and the variation was large.

Another single crystal plate having a {100} plane and a thickness of 0.26 mm and a size of 15 mm × 20 mm square was processed from the piezoelectric single crystal. By sputtering, Ti / Au electrodes (Ti thickness: 50 n
m, Au thickness: 500 nm). After the electrode formed on the side surface of the single crystal plate and a part of the electrode formed on the surface opposite to the ultrasonic wave receiving surface were removed by selective etching, polarization was performed in the same manner as described above. After forming an acoustic matching layer on the ultrasonic receiving surface of the single crystal plate, it was adhered on the backing material. A single crystal plate was cut from the acoustic matching layer using a diamond blade having a thickness of 0.03 mm, cut into strips at a pitch of 0.19 mm, and separated from each other having a first electrode and a second electrode on a backing material. One hundred piezoelectric vibrators were formed. An acoustic lens was formed on the acoustic matching layer. The conductive layer of the flexible printed wiring board was connected to each first electrode by soldering, and the ground electrode plate was connected to the second electrode by soldering. A plurality of cables each having a length of 2 m and 110 pF / m were connected to the flexible printed wiring board and the ground electrode plate, thereby manufacturing an array type ultrasonic probe. Using the obtained array type ultrasonic probe, the reflection echo was measured by the pulse echo method. As a result, only an echo having a center frequency of 2.5 MHz was recognized in 80% of all the elements. When the impedance characteristics of the elements cut into strips were measured, 20% of the elements were defective. The sensitivity of the element from which the echo was obtained is about 2 dB higher than that of the conventional PZT-based piezoelectric ceramics, but 5 to 7 dB lower than that of Example 1,
The sensitivity variation between the array elements was as large as 3 dB at the maximum. The frequency band is also -6dB, and the average value of the fractional band is 60%
It was confirmed that it was narrow.

Comparative Example 3 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed so that the molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ was 91: 9. In addition, P was added such that the molar ratio between the single crystal raw material powder (PZN-PT91 / 9) and the flux (PbO) was 45/55.
bO was weighed. These were mixed well, and the mixed powder was solidified with an isostatic press to produce 1000 g of pellets.

Inner diameter 40 mm × length 200 mm × thickness
A 5 mm platinum crucible having a platinum cooling rod with a thickness of 3 mm and a length of 100 mm provided at the center of the bottom surface was prepared. This crucible was filled with the pellets, covered with a platinum cover, and passed through a tubular furnace set at 1300 ° C. The moving speed was 0.2 mm / h. The time required for growing the single crystal was 50 days.

When the crucible was removed, the caliber was 40 mm.
Crystals having a length of 30 mm and 280 g were precipitated. When this crystal was examined by Laue photograph and X-ray diffraction method,
It was found that the material was a rhombohedral perovskite-type piezoelectric single crystal at room temperature. However, when this crystal was observed in detail, many cracks and dislocations were observed.

Comparative Example 4 Raw material powders of PbO, ZnO, Nb ₂ O ₅ and TiO _{2 having} a purity of 99.9% or more were prepared. Lead zinc niobate Pb
The raw material powder was weighed so that the molar ratio of (Zn _1/3 Nb _2/3 ) O ₃ to lead titanate PbTiO ₃ was 91: 9. In addition, P was added such that the molar ratio between the single crystal raw material powder (PZN-PT91 / 9) and the flux (PbO) was 45/55.
bO was weighed. These were mixed well, and the mixed powder was solidified with an isostatic press to produce 900 g of pellets.

An inner diameter of 40 mm × a length of 200 mm × a thickness of 0.1 mm.
A 2 mm platinum crucible having a platinum cooling rod having a thickness of 2 mm and a length of 100 mm provided at the bottom center was prepared. The crucible was filled with the above pellets, passed through a tubular furnace set at 1280 ° C. with a platinum lid. The moving speed was 0.2 mm / h.

However, a leakage of raw materials occurred on the 20th day after the start of the growth, and the crucible was cooled down to room temperature and observed in detail, and a pinhole was found. This is because PbO used as a flux was reduced and corroded platinum.

When the crucible was removed, the caliber was 40 mm.
Crystals having a length of 30 mm and 280 g were precipitated. When this crystal was examined by Laue photograph and X-ray diffraction method,
It was found that the material was a rhombohedral perovskite-type piezoelectric single crystal at room temperature. When this crystal was observed in detail, cracks and dislocations were not observed. However, it was observed that a large number of pyrochlore-type single crystals having low piezoelectric properties were attached around the single crystal. This is considered to be because the perovskite structure became unstable due to the outflow of PbO.

Comparative Example 5 The same pellet as in Comparative Example 4 was produced. Inner diameter 40mm ×
A 200 mm long x 0.15 mm thick platinum crucible, 2 mm thick x 100 m long provided at the bottom center
One having a cooling rod made of platinum of m was prepared. This crucible was filled with the pellets, and crystals were grown under the same conditions as in Comparative Example 4.

On the 15th day after the start of the growth, a hole was made in the crucible,
The breeding was stopped due to the outflow of raw materials. As a result, no single crystal was obtained. This is because PbO corroded platinum.

[0081]

As described above in detail, the use of the method of the present invention makes it possible to produce a piezoelectric single crystal exhibiting an excellent electromechanical coupling coefficient while suppressing composition fluctuation.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for manufacturing a piezoelectric single crystal according to the present invention.

FIG. 2 is a sectional view of a double crucible used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Crucible 2 ... Cooling rod 3 ... Piezoelectric single crystal 4 ... Melt 5 ... Sintered raw material 6 ... Heater 10 ... Double crucible 11 ... Inner wall 12 ... Outer wall 13 ... Cooling rod

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yohachi Yamashita 70 Yanagicho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Yanagimachi Plant Co., Ltd. Inside the Toshiba R & D Center (72) Inventor Shiro Saito 1st Kogashi Toshiba-cho, Saiwai-ku, Kawasaki City, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Mamoru Izumi Toshiba Komukai, Saiyuki-ku, Kawasaki City, Kanagawa Prefecture 1-cho, Toshiba R & D Center F-term (reference) 4G050 DA04 DB04 DB08 DB33 4G077 AA02 BC34 CD02 EG02 EG18 EH07 HA11

Claims (3)

[Claims] 1. A crucible containing a raw material containing lead oxide, niobium oxide and titanium oxide, forming a local temperature gradient by a heating source, heating the crucible, and moving the crucible to form a composite perovskite oxide In producing the piezoelectric single crystal, a solid body of lead oxide and a sintered body of a raw material constituting the piezoelectric single crystal are separately accommodated in the crucible, and the solid body of lead oxide is melted. When a melt is formed,
The diameter of the crucible is r (mm), and the height of the melt is h
A method for producing a piezoelectric single crystal, wherein (mm) is adjusted so as to be in the range of 3 ≦ h ≦ 200 and 0.03 ≦ h / r ≦ 10. 2. When the maximum temperature of the crucible is T _M , and the temperature of the crucible at a position away from the position where the crucible exhibits the maximum temperature by the diameter r of the crucible is T _R ,
The temperature distribution of the crucible is 1050 ° C. ≦ T _M ≦ 1250 ° C. and 50 ° C. ≦ T _M −T
_{2. The} method for producing a piezoelectric single crystal according to claim 1, wherein the temperature is set so that R.ltoreq.500.degree. 3. The method for producing a piezoelectric single crystal according to claim 1, wherein said crucible has a multi-layered structure and is formed of two or more materials.