CN1204085C - Ion dosed sodium barium titanate-barium titanate piezo ceramics and preparation thereof - Google Patents

Abstract

The invention relates to a piezoelectric ceramic doped with sodium bismuth titanate-barium titanate system and a preparation method thereof, belonging to the field of functional ceramics. The present invention selects 0.94(Bi1/2Na1/2)TiO ₃ -0.06BaTiO ₃ system piezoelectric ceramics as the matrix, mixes Co ³⁺ with a molar ratio of 0.5%-1.5%, controls the pre-synthesis temperature to be 800-1200°C, and the holding time 1-4 hours, the sintering temperature is 1150-1300° C., and the holding time is 1-4 hours. A new type of piezoelectric ceramic material obtained. Its piezoelectric constant d ₃₃ is increased to 139pC/N, thickness electromechanical coupling coefficient k _t is increased to 0.46, and the dielectric loss of the material is controlled at 0.02. The lead-free piezoelectric ceramic material can be used in various fields such as industrial flaw detection, thickness measurement, and medical ultrasonic diagnosis.

Description

Ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramics and preparation method thereof

technical field

The invention relates to the doping of (Na _1/2 Bi _1/2 )TiO ₃ -BaTiO ₃ system piezoelectric materials and belongs to the field of functional ceramics.

Background technique

Piezoelectric ferroelectric ceramics are widely used in functional ceramics, such as ferroelectric applications (memory), piezoelectric applications (transducers, sensors, drivers, filters, etc.), pyroelectric applications (infrared Detectors), dielectric applications (capacitors), etc., have played an important role in the national economy and national defense. Its output and output value are very large, and a large-scale industry has been formed. However, the vast majority of traditional piezoelectric ferroelectric ceramics are lead-containing ceramics, in which lead oxide (or PbO4) accounts for about 70% of the total mass of raw materials. Such materials are accompanied by severe oxidation during high-temperature sintering. The volatilization of lead causes environmental lead pollution and brings harm to the environment and human beings.

In recent years, with the demands of environmental protection and sustainable development of human society, the research and development of new environment-friendly ferroelectric piezoelectric ceramics has become one of the hot materials developed countries in the world are committed to research and development. However, limited to the nature of the lead-free piezoelectric ceramic material itself, it is much more difficult to improve its piezoelectric performance than lead-containing materials. Currently, it is reported that the d ₃₃ value of the rare piezoelectric constant in the lead-free piezoelectric ceramic can reach 100pC /N or more systems.

Sodium bismuth titanate (Bi _1/2 Na _1/2 )TiO ₃ , referred to as BNT) is an A-site composite perovskite-type lead-free and environment-friendly piezoelectric ceramic material. Pure sodium bismuth titanate single crystal has a large remanent polarization (P _r =38μC/cm ² ) and a very high coercive field (E _c =7.3kV/mm), and the polarization is very difficult. Substitution and modification can reduce its coercive field and make it easier to polarize to improve piezoelectric performance. At present, the BNT systems that have been studied in the world mainly include solid solution ceramics such as sodium bismuth titanate-barium titanate, SrTiO ₃ , (Sr _a Pb _b Ca _c )TiO ₃ , La ₂ (TiO ₃ ) ₃ , and BaTiO ₃ . Among these systems, (1-x)(Bi _1/2 Na _1/2 )TiO ₃ -xBaTiO ₃ has relatively excellent piezoelectric properties.

In addition, previous studies on piezoelectric ceramics have shown that in the quasi-isomorphic phase boundary region, the structure of the material is relatively relaxed, the two phases have similar free energy, and the free energy difference is not sensitive to temperature changes, so materials near the phase boundary It has excellent piezoelectric performance.

For the (1-x)(Bi _1/2 Na _1/2 )TiO _3- xBaTiO ₃ system, at room temperature, when x=0.06 (ie 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ ), that is, its quasi-isotype phase boundary composition, (abbreviated as BNBT6), and no research report on doping modification using this quasi-isotype phase boundary composition ceramic as a matrix has been found in the existing literature.

Contents of the invention

The purpose of the present invention is to further improve the piezoelectric performance of BNBT6 ceramics while controlling the ^dielectric loss as much as possible by doping 0.5%-1.5% Co in the BNBT6 matrix in a molar ratio. High d ₃₃ and electromechanical coupling coefficient k _t improve the practical value of lead-free piezoelectric ceramic materials.

The present invention is prepared by the following scheme.

The basic raw materials are prepared according to the molecular formula of 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ , the basic raw materials can be anhydrous sodium carbonate, barium carbonate, bismuth oxide, titanium dioxide; the molar ratio of the basic raw materials is 0.5%- 1.5% doped with Co ³⁺ ions, the selected dopant can be cobalt oxide.

Use anhydrous ethanol as the medium to roughly grind in a nylon ball mill for 8-16 hours. After discharging and drying, press the powder into blocks at a pressure of 40-80MPa, and increase the temperature at a rate of 2°C/min to 800-1200°C. Pre-synthesis is carried out by heat preservation for 1-4 hours; the obtained block is ground and passed through a 40-mesh sieve, and then finely ground for 24 hours with absolute ethanol as the medium, and dried. Add 7wt% binder (6wt% PVA aqueous solution) to the powder, pass through a 20-mesh sieve to granulate, and shape under a pressure of 100-300MPa. The molded green body was kept at 800°C for 2 hours (heating rate 2°C/min) for ejection. The sintering temperature is 1150-1300°C, the heating rate is 2°C/min, the crucible is sealed and sintered, and the temperature is kept for 1-4 hours. Polarized by applying voltage to silicon oil after being silver electrode.

The doped piezoelectric ceramic prepared by the invention controls K _t , K _p , Q _m and tgδ while increasing the dielectric constant by 50% and the piezoelectric constant by 16%.

Description of drawings

Figure 1 is a graph showing the relationship between bulk density and sintering temperature of BNBT6 doped 1% Co ³⁺ ceramics.

Detailed ways

Below in conjunction with embodiment further illustrate substantive characteristics and remarkable progress of the present invention. It should be noted that the present invention is not limited to the following examples.

Comparative example 1

The matrix is 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ , the raw materials used are anhydrous sodium carbonate (Na ₂ CO ₃ ), barium carbonate (BaCO ₃ ), bismuth oxide (Bi ₂ O ₃ ) , Titanium dioxide (TiO ₂ ).

Use anhydrous ethanol as the medium to roughly grind in a nylon ball mill for 12 hours. After the material is discharged and dried, the powder is pressed into blocks at a pressure of 60MPa. The heating rate is raised to 1000°C at a rate of 2°C/min, and the temperature is kept for 2 hours for pre-synthesis. ; Grind the obtained block and pass through a 40-mesh sieve, and then finely grind it for 24 hours with absolute ethanol as the medium, and dry it. Add 7wt% binder (6wt% PVA aqueous solution) to the powder, pass through a 20-mesh sieve to granulate, and shape under a pressure of 200MPa. The molded green body was kept at 800°C for 2 hours (heating rate 2°C/min) for ejection. The sintering temperature is set at 1200°C, the heating rate is 2°C/min, the crucible is sealed and sintered, and the temperature is kept for 2 hours. Polarize after being silver electrode, the polarization condition is 80 ℃ silicone oil, apply 4kV/mm voltage for 5 minutes.

Example 1

Add 1% molar ratio of Co ₂ O ₃ into the matrix 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ , the raw materials used are anhydrous sodium carbonate (Na ₂ CO ₃ ), barium carbonate (BaCO ₃ ), bismuth oxide (Bi ₂ O ₃ ), titanium dioxide (TiO ₂ ), cobalt oxide (Co ₂ O ₃ ).

The sintering temperature is 1160° C., the heating rate is 2° C./min, and other conditions are the same as those of Comparative Example 1. Polarize after being silver electrode, the polarization condition is 40 ℃ silicone oil, apply 4kV/mm voltage for 5 minutes.

Table 1 is a comparative table of properties measured after preparing samples of Comparative Example 1 and Example 1.

The test conditions are:

Bulk Density: Archimedes Drainage Method

Dielectric constant and dielectric loss: Measure the dielectric loss and capacitance C _p of the sample using a precision LCR analyzer HP4284 at an electric field frequency of 1KHz, and then calculate the dielectric constant by the formula ε _r =4C _p ·t/π·ε ₀ ·d ² electric constant.

Piezoelectric constant: Measured at 100Hz with a ZJ-3Ad33 measuring instrument.

Electromechanical coupling coefficients K _t , K _p : Measured by the overtone ratio method using an Agilent 4294 impedance analyzer.

Mechanical quality factor Q _m : Measured by the admittance circle method using an Agilent 4294 impedance analyzer.

Table 1 Comparative example 1 Example 1 Bulk density (g/cm ³ ) 5.65 5.58 Dielectric constant εT33 (electric field frequency 1kHz) 776 1200 Piezoelectric constant d ₃₃ (pC/N) 119 139 Dielectric loss tangent angle tgδ (electric field frequency 1kHz) 0.025 0.020 Thickness electromechanical coupling coefficient k _t 0.43 0.46 Planar electromechanical coupling coefficient k _p 0.28 0.27 Mechanical quality factor Q _m 256 253

Example 2

The sintering temperature is 1180° C., the holding time is 2 hours, the heating rate is 2° C./min, and other conditions are the same as in Example 1. The measured bulk density of the sample is: 5.50g/cm ³

Example 3

The sintering temperature is 1200° C., the holding time is 2 hours, the heating rate is 2° C./min, and other conditions are the same as in Example 1. The measured bulk density of the sample is: 5.48g/cm ³

Claims (7)

1. Ion-doped sodium bismuth titanate-barium titanate piezoelectric ceramics, characterized in that the piezoelectric ceramics of 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ system are used as the matrix and doped with Co ³⁺ , the doping amount is 0.5%-1.5% molar ratio of the matrix. 2. The ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramic according to claim 1, characterized in that the doping amount of Co ³⁺ is 1% molar ratio of the matrix. 3. A method for preparing ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramics, comprising batching, mixing, briquetting, pre-synthesis, forming, plastic discharge, and sintering, characterized in that: (1) The basic raw material is prepared according to the molecular formula of 0.94(Bi _1/2 Na _1/2 )TiO ₃ -0.06BaTiO ₃ , and the doping material is prepared according to the molar ratio of Co ³⁺ ions accounting for 0.5%-1.5% of the basic raw material; (2) The pre-synthesis temperature is 800-1200°C, and the holding time is 1-4 hours; (3) The sintering temperature is 1150-1300° C., and the holding time is 1-4 hours. 4. A method for preparing ion-doped bismuth sodium titanate-barium titanate system piezoelectric ceramics according to claim 3, characterized in that the doping is carried out according to the Co ³⁺ ion molar ratio accounting for 1% of the basic raw material material. 5. A method for preparing ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramics according to claim 4, characterized in that the sintering temperature is 1160°C and the holding time is 2 hours. 6. A method for preparing ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramics according to claim 3, 4 or 5, characterized in that the basic raw materials are anhydrous sodium carbonate, barium carbonate, oxide Bismuth, titanium dioxide, and cobalt oxide are selected as the dopant. 7. The ion-doped sodium bismuth titanate-barium titanate system piezoelectric ceramic according to claim 1 or 2 is used in the fields of industrial flaw detection, thickness measurement, and medical ultrasonic diagnosis.

Images