CN1272277C - Magneto-electric coupled ceramic materials and preparing method thereof - Google Patents

Abstract

The present invention discloses magneto-electric coupling ceramic material. The present invention has the chemical formula: Biological-xAxFe1-yByO3, wherein x is more than 0 or equal to 0, and less than 0.5; y is more than o or equal to 0, and less than 0.2; x and y can not be 0 simultaneously; A is one or two kinds of trivalent rare earth metal ions of La, Nd, Td, Sm and Pr; B is one kind of transition metal ions of Mn or Co. The material has the following physical property that the breakdown electric field is more than 150kV/ cm; the remanent polarization of the electropolar-electric field loop is between 3 to 30 mu C/cm<2>. Simultaneously, the present invention also discloses a preparation method of the material. The present invention has the invention point that the temperature rises at the temperature rise speed over 30 DEG C/minute during sintering; the sintering is carried out between 850 DEG C to 940 DEG C; then, cooling is carried out rapidly.

Description

A kind of magnetoelectric coupling ceramic material and preparation method thereof

technical field

The invention relates to a magnetoelectric coupling ceramic material and a preparation method thereof.

Background technique

Ferroelectric magnets or magnetoelectric coupling materials have both ferroelectricity and ferromagnetic (antiferromagnetic) properties, and coupling between ferroelectric polarization and ferromagnetic (antiferromagnetic) spins can occur, resulting in new physical effects, That is to say, the magnetism of such materials can be changed by applying an electric field or the ferroelectricity of such materials can be changed by applying a magnetic field. The ferromagnetic Curie temperature of general single-phase ferroelectromagnets is relatively low, for example, the ferromagnetic Curie temperature of Pb(Nb _1/2 Fe _1/2 )O ₃ is about -160°C. BiFeO ₃ is a rare material in the existing single-phase ferroelectric magnets with both ferroelectric Curie temperature (~700°C) and ferromagnetic Curie temperature (~370°C) above room temperature. The antiferromagnetism of BiFeO ₃ has sinusoidal fluctuations, so it only has a small second-order magnetoelectric coupling coefficient, but the Bi _1-x A _x Fe _1-y By _y O ₃ series ceramics (0≤x<0.5, 0≤y <0.2, A is one or two of rare earth metal ions La ³⁺ , Nd ³⁺ , Td ³⁺ , Sm ³⁺ , Pr ³⁺ , B is a trivalent metal ion Mn ³⁺ or Co ³⁺ ) is expected to break the sinusoidal fluctuations of antiferromagnetism and have a large first-order magnetoelectric coupling coefficient. Because BiFeO ₃ is very sensitive to the preparation conditions, the price change of trivalent Fe ions and the volatilization of Bi lead to poor insulation of ceramics; therefore, before the preparation method is solved, the Bi _1-x A _x Fe _1-y By _y O ₃ series Research on ceramics cannot be carried out effectively. At present, whether ABO ₃ -type perovskite single-phase ceramics with high insulation (resistivity ~ 10 ⁹ Ω·cm, breakdown electric field greater than 150kV/cm) can be successfully prepared depends on whether such ceramics and thin films can be effectively One of the key factors to develop research and optimize and be applied. At present, in this field, most people prepare Bi _1-x A _x Fe _1-y By O _{3 ceramics} through the general solid-state sintering method and use Bi ₂ O ₃ powder, so the sintering temperature is at the melting point of Bi ₂ O ₃ (817°C) below. However, because trivalent Fe ions are easy to change in value and Bi is easy to volatilize, it is difficult to obtain pure ABO ₃ phase ceramics by general solid-state sintering methods, so the resistivity is so low that it is impossible to obtain a saturated electrical polarization-electric field hysteresis. line (i.e. PV return line).

There are currently two well-known sintering methods specifically for BiFeO ₃ ceramics. The first is to dissolve the impurity phase formed by ordinary sintering method with diluted nitric acid, and then sinter the remaining pure phase to form ceramics. Ceramics prepared by this method, because it is difficult to completely remove the impurity phase, so the breakdown electric field still cannot reach ~150kV/cm, so it is impossible to saturate polarization of BiFeO ₃ ceramics [M.Mahesh Kumar, VRPalkar, K.Srinivas , and SV Suryanarayana, Applied Physics Letters 76, 2764 (2000).]. The second method uses NaOH to prepare the hydroxide mixture precipitate of the required ions, and then sinters the desired powder material at -550°C, and finally makes a ceramic target for pulsed laser deposition (PLD) or magnetron sputtering Growing Thin Films [VR Palkar, Darshan C. Kundaliya, and SK Malik, Indian Patent Application No. 409/MUM/2003, dated 24 April 2003.]. At present, Bi _1-x A _x Fe _1-y By _y O ₃ series ceramics have been prepared by the traditional solid-state sintering method, but the breakdown electric field of the ceramics prepared by them is very small, and it is difficult to measure the saturated polarization-electric field [AV Zalesskii, AAFrolov, TA Khimich, and AABush, Physics of the Solid State 45, 141 (2003); I.Sosnowska, W.Schfer, W.Kockelmann, KHAndersen, IOTroyanchuk, Appl.Phys.A 74, S1040( 2002); VL Mathe, KK Patankar, RN Patil, CD Lokhande, Journal of Magnetism and Magnetic Materials 270, 380 (2004); VL Mathe, Journal of Magnetism and Magnetic Materials 263, 344 (2003).]. The specific performance indicators of the ceramic materials reported in the above literature are introduced in Table 1. Therefore, the preparation of Bi _1-x A _x Fe _{1-y By} O ₃ with ABO ₃ single-phase structure with a resistivity of ∼10 ⁹ Ω·cm and a breakdown voltage of more than 150 kV/cm using a simple method has become an urgent Task.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the defects existing in the prior art, and provide a magnetoelectric coupling ceramic material Bi _1-x A _x Fe _{1-y By} O ₃ , which has the following physical properties: the breakdown electric field is greater than 150kV /cm, the remnant polarization of the polarization-electric field loop of the ferroelectric magnet is between 3-30μC/cm ² .

Another object of the present invention is to provide a method for preparing the above-mentioned ceramic material. The ceramic material prepared by the inventor has the following physical properties: the breakdown electric field is greater than 150kV/cm, and the polarization of the ferroelectric magnet-the remnant pole of the electric field loop be between 3 and 30 μC/cm ² .

The above physical and chemical properties are not available in existing materials.

The magnetoelectric coupling ceramic material of the present invention is characterized in that:

(1) The chemical formula is

Bi _1-x A _x Fe _1-y By _y O ₃

Among them: 0≤x<0.5, 0≤y<0.2 and x and y cannot be 0 at the same time;

A is one or two of the trivalent rare earth metal ions La, Nd, Td, Sm, and Pr;

B is a transition metal ion Mn or Co;

(2) Has the following physical properties

The breakdown electric field is greater than 150kV/cm, and the remnant polarization of the polarization-electric field loop of the ferroelectric magnet is between 3 and 30μC/cm ² .

The method for preparing above-mentioned ceramic material, its step is:

a) Using Bi ₂ O ₃ , La ₂ O ₃ , Fe ₂ O ₃ , Td ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Mn ₂ O ₃ , Co ₂ O ₃ , Pr ₂ O ₃ powder or corresponding Carbonate and nitrate powder as raw materials, according to Bi _1-x A _x Fe _{1-y By} O ₃ (0≤x<0.5, 0≤y<0.2, A is rare earth metal ions La ³⁺ , Nd ^{3 +} , Td ³⁺ , Sm ³⁺ , Pr ³⁺ one or both, B is a trivalent metal ion Mn ³⁺ or Co ³⁺ . The specific composition is shown in Table 2) The stoichiometric ratio of series ceramics .

b) Mix the powders of the ingredients evenly, and the average particle size of the mixture is less than 1.0 micron.

c) Use a volatile liquid such as water as a binder, mix the mixture and the binder evenly, and then press the target. The thickness of the target is 0.5 mm. Reducing the thickness of the target is conducive to the rapid conduction of heat from the surface to the center of the target during the sintering process, which is conducive to increasing the heating rate of the target.

d) Use a vacuum or non-vacuum oven to completely volatilize the binder in the mixture below 400°C. The use of easily volatile binders and the removal of binders before rapid heating and sintering is to avoid the volatilization and absorption of heat by binders during sintering, thereby reducing the heating rate during sintering, so that the 30°C/s ( degrees/second) above the temperature rise conditions.

e) Use rapid heat treatment RTA, tube furnace or other furnaces to sinter ceramics, and heat up at a rate of 30°C/s (degrees/second) or more, between 820°C (817°C higher than the melting point of Bi ₂ O ₃ ) to 940°C The Bi _1-x A _x Fe _1-y By _y O ₃ series ceramics were sintered between 1 minute and 1 hour, and the temperature was rapidly lowered at the end. The sintered ceramics form ABO ₃ single phase, the resistivity can reach ~10 ⁹ Ω·cm and the breakdown electric field is greater than 150kV/cm.

If you want to prepare larger targets for PLD or magnetron sputtering. The further optimization scheme of the inventive method is: on the basis of above-mentioned method, increase following steps:

f) Grind the target successfully prepared in the previous step into powder, add appropriate amount of water to the powder, mix well, and then prepare a large target again. Put the large target in an oven at 100°C to 400°C and keep it warm for more than 12 hours to let the water fully evaporate, and finally let the target heat up to above 800°C at a speed of more than 50°C/s (degrees/second), and keep it warm at this temperature Within 60 minutes.

Detailed ways

The following examples can enable those skilled in the art to understand the present invention more fully, but do not limit the present invention in any way.

Table 1. Bi _1-x A _x Fe _1-y By _y O ₃ ceramic materials prepared by others and their remanent polarization and breakdown voltage

The specific preparation method of the magnetoelectric coupling ceramic material of the present invention:

a) Using Bi ₂ O ₃ , La ₂ O ₃ , Fe ₂ O ₃ , Td ₂ O ₃ , Nd ₂ O ₃ , Sm ₂ O ₃ , Mn ₂ O ₃ , Co ₂ O ₃ , Pr ₂ O ₃ powder or corresponding According to Bi _1-x A _x Fe _1-y By _y O ₃ (0≤x<0.5, 0≤y<0.2, A is the trivalent rare earth metal ion La ³⁺ , One or two of Nd ³⁺ , Td ³⁺ , Sm ³⁺ , Pr ³⁺ , B is one of transition metal ions Mn ³⁺ , Co ³⁺ , see Table 2 for the chemical composition of series ceramics than toppings.

b) After batching, put the powder into an agate jar and grind for more than 12 hours, so that the powder is evenly mixed, and the average particle size of the powder is less than 1.0 microns.

c) Dry the evenly mixed powder, and then add just the right amount of water as a binder. The mixture was pressed into a target with a thickness of 0.5 mm. Reducing the thickness of the target is conducive to the rapid conduction of heat from the surface to the center of the target during the sintering process, which is conducive to increasing the heating rate of the target.

d) Adjust the temperature of the oven to 150°C, and keep the target in the oven for more than 10 hours, so as to fully volatilize the water vapor contained in the target. Using water as a binder and letting it evaporate before sintering is to avoid the volatilization of water absorbing heat during rapid heating and sintering, thereby reducing the heating rate during sintering.

e) Sinter Bi _1-x A between 820°C (817°C above the melting point of _Bi2O3 ) and 940°C using rapid thermal treatment (RTA) at a rate of ₃₀ °C/s (degrees/second) or more _x Fe _{1-y By} O ₃ series ceramics, the sintering time is between 1 minute and 1 hour. For example, the sintered BiFeO ₃ sample is heated to 870 degrees within 30 seconds, then kept at 870 degrees for 5 minutes, and then cooled to below 500 degrees within 5 minutes. The sintered ceramics form ABO ₃ single phase, the resistivity can reach -10 ⁹ Ω·cm and the breakdown electric field is greater than 150kV/cm.

f) If you want to prepare larger targets used in PLD or magnetron sputtering. Grind the target successfully sintered in the previous step into powder, add water as a binder, and press it into a large target again, then let the water fully evaporate in an oven, and sinter at 817°C for less than 1 hour. For example, the BiFeO ₃ sample is heated to 830°C at a speed of 50°C/s (degrees/second) and kept for 10 minutes.

The magnetoelectric coupling ceramic material prepared by the inventor according to the above invention method and the test results of its physical properties are shown in Table 2.

Table 2

Claims (5)

1, a kind of magneto-electric coupled ceramic materials is characterized in that:

(1) chemical formula is

Bi _1-xA _xFe _1-yB _yO ₃

Wherein: 0≤x＜0.5,0≤y＜0.2 and x, y can not be 0 simultaneously;

A is one or both among rare earth cation La, Nd, Td, Sm, the Pr;

B is transition metal ion Mn or Co;

(2) has following physicals

Breakdown electric field is greater than 150kV/cm, and the residual polarization of electropolarization-electric field loop line is at 3～30 μ C/cm ²Between.

2, magneto-electric coupled ceramic materials according to claim 1 is characterized in that: described stupalith makes with following method:

When sintering, the heat-up rate above with 30 degree/seconds heats up, and sintering between 820 ℃ to 940 ℃ was cooled to below 500 degree with interior at 5 minutes then.

3, magneto-electric coupled ceramic materials according to claim 1 is characterized in that: described stupalith makes with following method:

A) utilize Bi ₂O ₃, La ₂O ₃, Fe ₂O ₃, Td ₂O ₃, Nd ₂O ₃, Sm ₂O ₃, Mn ₂O ₃, Co ₂O ₃, Pr ₂O ₃Powder or corresponding carbonate and nitrate powder are as raw material, according to Bi _1-xA _xFe _1-yB _yO ₃The stoicheiometry batching of pottery;

B) even the powder mixes of batching, the average grain of mixture is less than 1.0 microns;

C) make water as tackiness agent, mixture and tackiness agent are mixed, press target again;

D) in the tackiness agent volatilization that allows below 400 ℃ in the mixture;

E) with above heat-up rate intensification 30 degree/seconds, sintering between 820 ℃ to 940 ℃, sintering time were cooled to below 500 degree with interior at 5 minutes between 1 minute to 1 hour then.

4, the preparation method of a kind of claim 1,2 or 3 described magneto-electric coupled ceramic materials the steps include:

A) utilize Bi ₂O ₃, La ₂O ₃, Fe ₂O ₃, Td ₂O ₃, Nd ₂O ₃, Sm ₂O ₃, Mn ₂O ₃, Co ₂O ₃, Pr ₂O ₃Powder or corresponding carbonate and nitrate powder are as raw material, according to Bi _1-xA _xFe _1-yB _yO ₃The stoicheiometry batching of pottery;

B) even the powder mixes of batching, the average grain of mixture is less than 1.0 microns;

C) make water as tackiness agent, mixture and tackiness agent are mixed, press target again;

D) in the tackiness agent volatilization that allows below 400 ℃ in the mixture;

E) with above heat-up rate intensification 30 degree/seconds, sintering between 820 ℃ to 940 ℃, sintering time were cooled to below 500 degree with interior at 5 minutes between 1 minute to 1 hour then.

5, the preparation method of magneto-electric coupled ceramic materials according to claim 4 is characterized in that:

F) previous step is prepared successful target grind into powder again, in powder, add suitable quantity of water, mix, prepare big target then again; Big target was put into 100 ℃～400 ℃ baking oven insulation more than 12 hours, allowed water fully volatilize, and relief target is warming up to more than 800 ℃ with the above speed of 50 ℃/s, and in insulation under this temperature 60 minutes.