CN103708826A - Low dielectric-loss barium strontium titanate pyroelectric ceramic and preparation method thereof - Google Patents

Abstract

The invention relates to a low dielectric loss barium strontium titanate pyroelectric ceramic and a preparation method thereof, wherein the chemical composition of the strontium barium titanate pyroelectric ceramic is (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ , where 0.001≤x≤0.01, 0<a<1, 0≤b≤0.01, a+b<1, A is selected from Mn, Fe, Cu, K, Na, Al, Mg . The dielectric loss of the BST pyroelectric ceramics of the present invention is small, which can reach below 0.5% (zero bias field), and the sample has high purity, high performance, and good uniformity, which can meet the requirements of making uncooled infrared focal plane devices, and effectively The problem of large dielectric loss of BST ceramics is solved.

Description

Low dielectric loss strontium barium titanate pyroelectric ceramics and preparation method thereof

technical field

The invention belongs to the field of inorganic material preparation, specifically relates to the technical field of pyroelectric ceramic materials, and provides a low dielectric loss barium strontium titanate pyroelectric ceramic and a preparation method thereof.

Background technique

Barium strontium titanate (Ba _x Sr _1-x TiO ₃ (0<x<1), BST) ceramic material has the characteristics of adjustable Curie temperature, high dielectric constant, high pyroelectric coefficient, etc. An important candidate material for electrically uncooled infrared focal planes.

When making uncooled infrared focal plane devices, BST pyroelectric ceramics adopt a new dielectric working mode, that is, an external DC bias electric field is required to obtain the required pyroelectric performance. After applying a DC bias electric field, if the dielectric loss of BST ceramics is high, it is easy to cause poor electrical insulation performance and high conductivity, which makes the leakage current of BST ceramics too large to be used. In addition, in the evaluation of infrared focal plane devices, the detection rate figure of merit F _d is a very important parameter, and F _d is closely related to the dielectric loss of BST ceramics (the formula is as follows):

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; p</span>}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}}\sqrt{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&delta;</span>}}}$

Where p is the pyroelectric coefficient, _Cv is the specific heat capacity, ε is the dielectric constant, and tanδ is the dielectric loss;

The lower the dielectric loss and the higher the _Fd , the better the performance of the device. Therefore, BST ceramics are also required to have low dielectric loss.

However, under normal circumstances, the dielectric loss of pure BST ceramics is relatively high, and the dielectric loss at the Curie temperature is generally above 1%. The requirement of cooled infrared focal plane devices is a technical bottleneck in the current research of BST pyroelectric ceramics.

Contents of the invention

Facing the problems existing in the prior art, the present invention provides a low dielectric loss BST pyroelectric ceramic and a preparation method thereof, so as to meet the requirements of current uncooled infrared focal plane devices for BST materials.

Here, the present invention firstly provides a low dielectric loss barium strontium titanate pyroelectric ceramic, the chemical composition of which is (Ba _{1-a- b Sra} ) _1-x La _x Ti _1-b A _b O ₃ , Wherein 0.001≤x≤0.01, 0<a<1, 0≤b≤0.01, a+b<1, A is selected from Mn, Fe, Cu, K, Na, Al, Mg.

Preferably, the dielectric loss of the low dielectric loss barium strontium titanate pyroelectric ceramic at the Curie temperature under zero bias field is ≤0.5%.

The dielectric loss of the BST pyroelectric ceramics of the present invention is small, which can reach below 0.5% (zero bias field), and the sample has high purity, high performance, and good uniformity, which can meet the requirements of making uncooled infrared focal plane devices, and effectively The problem of large dielectric loss of BST ceramics is solved.

In addition, the present invention also provides a method for preparing the above-mentioned low dielectric loss strontium barium titanate pyroelectric ceramics, comprising:

(1) Weigh the raw materials BaCO ₃ , SrCO ₃ , TiO ₂ , La ₂ O ₃ , oxides of A and/or carbonates of A according to the stoichiometric ratio, and mix them evenly by wet ball milling. After drying, press Add 4-10wt% deionized water to the weight of the raw material to briquette, and keep warm at 1000-1200°C for 1-3 hours in an air atmosphere to obtain strontium barium titanate block; Grinding and sieving to obtain (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder;

(2) The obtained (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder was mixed uniformly by wet ball milling process, after drying, a specified amount of binder was added, and after granulation, Aging, pre-pressing after sieving, isostatic pressing, and plastic discharge to obtain a barium strontium titanate green body; and

(3) The obtained barium strontium titanate body is sintered at 1350-1450° C. in an oxygen atmosphere to obtain the low dielectric loss barium strontium titanate ceramic.

The preparation method of the invention has the advantages of simple process, no need for special equipment, low cost, etc., is suitable for large-scale production, and can meet the needs of industrialization.

Preferably, in step (1), the wet ball milling process conditions can be: the mass ratio of raw materials, ball milling medium and deionized water is 1: (1.0~2.0): (1.0~1.5), and the ball milling time is 12~ 26 hours, the ball milling medium is agate balls.

Preferably, in step (1), (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ powder is obtained by passing through a 40-mesh sieve.

Preferably, in step (2), the wet ball milling process conditions can be: (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ powder, ball milling medium and deionized water The mass ratio is 1:(1.5-2.0):(0.5-1.0), the ball milling time is 24-48 hours, and the ball milling medium is agate balls.

Preferably, in step (2), the binder is a polyvinyl alcohol solution with a mass concentration of 2-5%, and the amount of the binder added can be (Ba _1-ab Sr _a ) _{1 -x} La _x Ti _1-b A _b O ₃ powder mass 2~5%.

Preferably, in step (2), the aging time may be 22-26 hours, and the ejection temperature may be 750-850°C.

Preferably, in step (3), the sintering process conditions can be: heating up at a rate of 1-4°C/min, passing oxygen during the sintering process, the oxygen flow rate is 1-3L/mi, when the temperature rises to 1350 At ~1450°C, keep warm for 1-5 hours, then cool down to room temperature with the furnace, and turn off the oxygen.

The invention effectively solves the problem of high dielectric loss of pure BST ceramics, and has a simple preparation method, short cycle and low cost, is suitable for large-scale production, can meet the needs of practical applications, and has broad application prospects.

Description of drawings

Fig. 1 is the scanning electron micrograph of the low dielectric loss BST pyroelectric ceramics that embodiment 1 makes through surface polishing, thermal corrosion;

Fig. 2 is the low dielectric loss BST pyroelectric ceramics that embodiment 1 makes the variation graph of dielectric constant and dielectric loss with temperature under zero electric field;

Fig. 3 is the low dielectric loss BST pyroelectric ceramics that embodiment 1 makes under the external DC bias electric field (850V/mm) The variation graph of dielectric constant and dielectric loss with temperature;

Fig. 4 is a graph showing the variation curves of the dielectric constant and dielectric loss with temperature of the BST pyroelectric ceramics prepared in the comparative example without applying a direct current electric field.

Detailed ways

Specific embodiments are given below and the present invention is further described in conjunction with the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

The preparation method provided by the invention may comprise the following steps:

First, according to the general formula (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ , where 0.001≤x≤0.01, 0<a<1, 0≤b≤0.01, a+b<1 , A is selected from Mn, Fe, Cu, K, Na, Al, Mg to weigh the stoichiometric ratio of BaCO ₃ , SrCO ₃ , TiO ₂ , La ₂ O ₃ and the oxide of A and/or the carbonate of A, etc. Raw material powder. The raw material powder is mixed evenly by wet ball milling process. The wet ball milling process conditions can be: the mass ratio of raw material powder, ball milling medium and deionized water can be 1:(1.0～2.0):(1.0～1.5), the ball milling time is 12～26 hours, and the ball milling medium can be Features agate balls.

After drying, add deionized water to briquetting, synthesize in the air, the synthesis temperature can be 1000-1200°C, and the holding time can be 1-3 hours to obtain BST blocks. The amount of deionized water added can be 4-10wt% of the raw material powder.

The obtained BST block is crushed and sieved (eg 40 mesh sieve) to obtain (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ powder.

The obtained (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder is mixed uniformly by using a wet ball milling process, and the wet ball milling process conditions can be: (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder, ball milling medium and deionized water mass ratio can be 1:(1.5～2.0):(0.5～1.0), ball milling time is 24～48 hours, The ball milling media can be agate balls.

Drying after discharge, adding a certain amount of binder, pre-pressing after granulation, aging, sieving, isostatic pressing, and plastic discharge, to obtain the BST embryo body. The binder can be a polyvinyl alcohol (PVA) solution with a mass concentration of 2% to 5%, and the amount of the PVA solution can be 2% to 5% of the mass of the BST powder. The aging time may be 22-26 hours. The temperature of the plastic ejection may be 750-850°C.

The obtained BST body is sintered in an oxygen atmosphere. The sintering process conditions can be: heating up at a rate of 1-4°C/min, passing oxygen during the sintering process, and the flow rate of oxygen is 1-3L/mi. When the temperature rises to 1350- At 1450°C, keep it warm for 1 to 5 hours, then cool down to room temperature with the furnace, and turn off the oxygen to obtain low dielectric loss BST ceramics.

The sintered sample was processed into the required size, ultrasonically cleaned, silver paste was screen printed, dried, and kept at 700°C for 30 minutes, and the dielectric and pyroelectric properties of the sample were tested under DC bias. Fig. 1 is a scanning electron micrograph of an example BST pyroelectric ceramic of the present invention after surface polishing and thermal corrosion. It can be seen from Figure 1 that ceramics have few pores, high density, and small grain size. Fig. 2 is the variation graph of dielectric constant and dielectric loss with temperature under the BST pyroelectric ceramics of the example of the present invention without adding DC electric field, as seen from Fig. 2: the Curie temperature of ceramic is near room temperature, and dielectric constant is at 10 ³ orders of magnitude, the dielectric loss at the Curie temperature is 0.45%. Fig. 3 is a curve diagram of the change of dielectric constant and dielectric loss with temperature under the applied DC electric field (850V/mm) of BST pyroelectric ceramics of the present invention. It can be seen from Fig. 3 that the Curie temperature of ceramics is higher than that under zero electric field, But still around room temperature, the dielectric loss is lower, and the dielectric loss at the Curie temperature is only 0.35%. It can be seen that the BST pyroelectric ceramics prepared by the present invention have low dielectric loss (under zero electric field, the dielectric loss at the Curie temperature does not exceed 0.45%), and excellent microstructure, such as less pores, high density, crystal The particle size is fine and uniform, which can meet the requirements of making uncooled infrared focal plane devices. The invention effectively solves the problem of high dielectric loss of BST ceramics, has a simple preparation method, short cycle and low cost, is suitable for large-scale production, and can meet the needs of practical applications.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific temperature, time, feeding amount, etc. of the following examples are only an example of a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific numerical values exemplified below .

Example 1

Weigh raw material powders BaCO ₃ (801.87g), SrCO ₃ (288.57g), TiO ₂ (480.64g) and La ₂ O ₃ (6.85g), and 0.69g MnCO ₃ powder, and make all The powder is mixed evenly; the mass ratio of material, ball milling medium and deionized water is 1:1.5:1.2, the ball milling time is 24 hours, and the ball milling medium is agate balls.

Dry the abrasive, add deionized water with 4% of the total powder mass, briquette, and synthesize in the air at a synthesis temperature of 1150°C and a holding time of 2 hours to obtain BST blocks; pulverize, pass through a 40-mesh sieve, and use wet The ball milling process makes the powder mix evenly; the mass ratio of material, ball milling medium and deionized water is 1:2.0:0.8, the ball milling time is 48 hours, and the ball milling medium is agate balls.

Drying, adding PVA solution as a binder, granulating, aging for 24 hours, sieving, pre-pressing and isostatic pressing, the blank is discharged at 800°C to obtain a BST green body; the BST green body Sintering under oxygen, the sintering conditions are: heating up at a rate of 2.0°C/min; passing oxygen, the oxygen flow rate is 2L/min; when the temperature rises to 1350°C, keep it warm for 5 hours; cool down to room temperature, and turn off the oxygen.

The sintered sample was processed into the required size, ultrasonically cleaned, silver paste was screen printed, dried, and kept at 700°C for 30 minutes, and the dielectric and pyroelectric properties of the sample were tested under DC bias.

Fig. 1 is a scanning electron micrograph of the BST pyroelectric ceramics prepared in this example after surface polishing and thermal corrosion. It can be seen from Figure 1 that ceramics have few pores, high density, and small grain size.

Fig. 2 is the BST pyroelectric ceramics prepared in the present embodiment, the dielectric constant and the dielectric loss change curves with temperature without adding a direct current electric field, as can be seen from Fig. 2: the Curie temperature of ceramics is near room temperature, and the dielectric The constant is on the order of 10 ³ , and the dielectric loss at the Curie temperature is 0.45%, which is only about 1/5 compared to the BST ceramics doped with the same proportion of Y in the following comparative examples.

Fig. 3 is the BST pyroelectric ceramics prepared in this example under the applied DC electric field (850V/mm) dielectric constant and dielectric loss curves with temperature, it can be seen from Fig. 3: the Curie temperature of ceramics is lower than zero The electric field is high, but it is still near room temperature, and the dielectric loss is lower. The dielectric loss at the Curie temperature is only 0.35%.

comparative example

Weigh raw material powders BaCO ₃ (801.87g), SrCO ₃ (288.57g), TiO ₂ (480.64g) and Y ₂ O ₃ (4.74g), and 0.69g MnCO ₃ powder, and make all The powder is mixed evenly; the mass ratio of material, ball milling medium and deionized water is 1:1.5:1.2, the ball milling time is 24 hours, and the ball milling medium is agate balls.

Dry the abrasive, add deionized water with 4% of the total powder mass, briquette, and synthesize in the air at a synthesis temperature of 1150°C and a holding time of 2 hours to obtain BST blocks; pulverize, pass through a 40-mesh sieve, and use wet The ball milling process makes the powder mix evenly; the mass ratio of material, ball milling medium and deionized water is 1:2.0:0.8, the ball milling time is 48 hours, and the ball milling medium is agate balls.

Drying, adding PVA solution as a binder, granulating, aging for 24 hours, sieving, pre-pressing and isostatic pressing, the blank is discharged at 800°C to obtain a BST green body; the BST green body Sintering under oxygen, the sintering conditions are: heating up at a rate of 2.0°C/min; passing oxygen, the oxygen flow rate is 2L/min; when the temperature rises to 1350°C, keep it warm for 5 hours; cool down to room temperature, and turn off the oxygen.

The sintered sample was processed into the required size, ultrasonically cleaned, silver paste was screen printed, dried, and kept at 700°C for 30 minutes, and the dielectric and pyroelectric properties of the sample were tested under DC bias.

Fig. 4 is the BST pyroelectric ceramics prepared in this comparative example, the dielectric constant and the dielectric loss change curves with temperature under no direct current electric field. It can be seen from Fig. 4: the Curie temperature of ceramics is near room temperature, and the dielectric The constant is on the order of 10 ⁴ , and the dielectric loss at the Curie temperature is 2.37%.

In summary, the BST pyroelectric ceramics prepared by the present invention have low dielectric loss (under zero electric field, the dielectric loss at the Curie temperature does not exceed 0.45%), and excellent microstructure, such as less pores, dense High, fine and uniform grain size, which can meet the requirements of making uncooled infrared focal plane devices.

Industrial applicability: The BST pyroelectric ceramics prepared by the invention has low dielectric loss and can meet the requirements for making uncooled infrared focal plane devices. The invention effectively solves the problem of high dielectric loss of BST ceramics, has a simple preparation method, short cycle and low cost, is suitable for large-scale production, and can meet the needs of practical applications.

Claims (9)

1. A low dielectric loss barium strontium titanate pyroelectric ceramic, characterized in that its chemical composition is (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ , wherein 0.001≤ x≤0.01, 0<a<1, 0≤b≤0.01, a+b<1, A is selected from Mn, Fe, Cu, K, Na, Al, Mg. 2. low dielectric loss strontium barium titanate pyroelectric ceramics according to claim 1, is characterized in that, described low dielectric loss strontium barium titanate pyroelectric ceramics at Curie temperature place under zero bias field Dielectric loss ≤ 0.5%. 3. A preparation method of low dielectric loss strontium barium titanate pyroelectric ceramics according to claim 1 or 2, characterized in that it comprises: (1) Weigh the raw materials BaCO ₃ , SrCO ₃ , TiO ₂ , La ₂ O ₃ , oxides of A and/or carbonates of A according to the stoichiometric ratio, and mix them evenly by wet ball milling. After drying, press Add 4-10wt% deionized water to the weight of the raw material to briquette, and keep warm at 1000-1200°C for 1-3 hours in an air atmosphere to obtain strontium barium titanate block; Grinding and sieving to obtain (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder; (2) The obtained (Ba _1-ab Sr _a ) _1-x La _x Ti _1-b A _b O ₃ powder was mixed uniformly by wet ball milling process, after drying, a specified amount of binder was added, and after granulation, Aging, pre-pressing after sieving, isostatic pressing, and plastic discharge to obtain a barium strontium titanate green body; and (3) The obtained barium strontium titanate body is sintered at 1350-1450° C. in an oxygen atmosphere to obtain the low dielectric loss barium strontium titanate ceramic. 4. The preparation method according to claim 3, characterized in that, in step (1), the wet ball milling process conditions are: the mass ratio of raw materials, ball milling medium and deionized water is 1: (1.0-2.0): (1.0～1.5), the ball milling time is 12～26 hours, and the described ball milling medium is agate ball. 5. The preparation method according to claim 3 or 4, characterized in that, in step (1), (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b is prepared by passing through a 40-mesh sieve O ₃ powder. 6. The preparation method according to any one of claims 3-5, characterized in that, in step (2), the wet ball milling process conditions are: (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b The mass ratio of A _b O ₃ powder, ball milling medium and deionized water is 1:(1.5-2.0):(0.5-1.0), the ball milling time is 24-48 hours, and the ball milling medium is agate balls. 7. The preparation method according to any one of claims 3 to 6, characterized in that, in step (2), the binder is a polyvinyl alcohol solution with a mass concentration of 2 to 5%, and the The addition amount of the binder is 2-5% of the mass of the (Ba _{1-ab Sra} ) _1-x La _x Ti _1-b A _b O ₃ powder. 8. The preparation method according to any one of claims 3-7, characterized in that, in step (2), the aging time is 22-26 hours, and the temperature of the plastic discharge is 750- 850°C. 9. The preparation method according to any one of claims 3-8, characterized in that in step (3), the sintering process conditions are: heating at a rate of 1-4°C/min, the sintering process Oxygen is passed through the medium, and the oxygen flow rate is 1-3L/mi. When the temperature rises to 1350-1450°C, keep it warm for 1-5 hours, then cool down to room temperature with the furnace, and turn off the oxygen.

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