CN1927766A - Method of preparing pyroelectric ceramics - Google Patents

Abstract

The invention discloses a method for preparing pyroelectric ceramics, comprising: ① mixing MgO and Nb ₂ O ₅ uniformly at a mass ratio of 1:1, and synthesizing MgNb ₂ O ₆ with heat preservation; ② according to the chemical formula Pb _1+d [(Zr _x Ti _1－x ) _1－y (Mg _1/3 Nb _2/3 ) _y ]O ₃ +z at%Mn, 0.65≤x≤0.95, 0≤y≤0.3, 0≤d≤0.1, 0≤z ≤5, mix MgNb ₂ O ₆ with PbO, ZrO ₂ , TiO ₂ and Mn(NO ₃ ) ₂ solution, the mass concentration of Mn(NO ₃ ) ₂ solution is 2%; Sieve, preform and form, and then heat-preserve and sinter. The sintering adopts a double-crucible sealed atmosphere to overlap the sintering process, so that the sintering process is carried out in a saturated lead atmosphere; ④ Grind, clean, silver and sinter the sintered material; The material is placed in silicone oil at 100-120°C and polarized with an electric field of 3-5KV/mm for 15-30 minutes, and then cooled to room temperature under pressure. The present invention carries out effective manganese doping in the form of Mn(NO ₃ ) ₂ solution, and the prepared PMN-PZT pyroelectric ceramic has high pyroelectric coefficient, low dielectric loss and suitable dielectric constant, It has good comprehensive pyroelectric performance and meets the requirements for making pyroelectric infrared detectors.

Description

A method for preparing pyroelectric ceramics

technical field

The invention belongs to a method for preparing pyroelectric ceramic materials, in particular to the preparation of high-performance zirconium-rich lead magnesium niobate-lead zirconate titanate (PMN-PZT) ceramics.

Background technique

Among various materials, pyroelectric ceramic materials have a series of advantages such as simple manufacturing process, low cost, stable and reliable performance, easy processing, good mechanical properties, and high electric strength, making them suitable for high temperature, large area, large batch, The use under high power and harsh environment conditions shows its superiority. The most commonly used pyroelectric ceramics are lead titanate, lead zirconate titanate and lead zirconate titanate ceramics modified with rare earth elements. At present, conventional ceramics are mainly used in commercial production. This kind of ceramics is usually formed by adding a third phase to PZT binary system ceramics to form a ternary system, and then improve the thermoelectric performance through various trace additions. The material is characterized by a linear pyroelectric coefficient and a high thermoelectric figure of merit in a wide temperature range. The material has high mechanical strength, good processing performance, good consistency and repeatability, and is suitable for industrial production of detectors. The yield rate in the process is high.

In order to improve the performance of the detector and break through the limitations of conventional pyroelectric ceramics on the performance of the detector, people try to use some special properties of the material. Because the material is near the phase boundary or due to the instability of the composition or the change of the structure during the phase transition, various good thermoelectric and dielectric properties often appear. Realizing this purpose with the pyroelectric effect during phase transition becomes the research goal. The zirconium-rich PZT material exhibits a very high pyroelectricity due to a phase transition from a low-temperature trigonal phase to a high-temperature trigonal phase, that is, a ferroelectric-ferroelectric phase transition, and the spontaneous polarization of the material changes during the phase transition. The coefficient, the dielectric constant of the material during the phase change process does not change much, and remains at a relatively low level, so the material in this phase change region has a relatively good value for pyroelectric detection. Zirconium-rich PZT materials have become one of the hotspots in the application of pyroelectric detectors due to their special properties.

For the PMN-PZT (lead magnesium niobate-lead zirconate titanate) series materials, previous studies have focused on the piezoelectric properties near the quasi-phase boundary, or on the pyroelectric properties near the PT side of the phase diagram. Shaw CP and Whatmore RW et al. studied the pyroelectric properties of PMN-PZT in the zirconium-rich region, and studied PMN-PZT ceramics F _RL -F _RH (low-temperature ferroelectricity by changing the ratio of PMN and PT in PMN-PZT solid solution Phase-high-temperature ferroelectric phase) phase transition temperature changes, as well as the corresponding dielectric properties and pyroelectric properties. At the same time, they also found that manganese doping can effectively reduce the dielectric constant and dielectric loss of PMN-PZT ceramics. It can be seen from the expression F _D =p/Cv(εtanδ) ^1/2 of the pyroelectric detection figure of merit among the important parameters of pyroelectric materials that a pyroelectric material with good performance should have a high pyroelectric coefficient p, low dielectric loss tanδ and appropriate dielectric constant ε, so manganese doping can effectively improve the pyroelectric performance of PMN-PZT ceramics.

Contents of the invention

The object of the present invention is to provide a method for preparing pyroelectric ceramics, the pyroelectric ceramics prepared by the method have lower loss and dielectric constant, higher pyroelectric coefficient, and higher detection merit .

A kind of method for preparing pyroelectric ceramic provided by the invention, its step comprises:

(1) Mix MgO and Nb ₂ O ₅ evenly in a mass ratio of 1:1, and keep warm at 900-1100°C for 4-6 hours to synthesize MgNb ₂ O ₆ ;

(2) According to the chemical formula Pb _1+d [(Zr _x Ti _1-x ) _1-y (Mg _1/3 Nb _2/3 ) _y ]O ₃ +z at% Mn, where 0.65≤x≤0.95, 0≤y≤0.3, 0≤d≤0.1, 0≤z≤5, mix the synthesized MgNb ₂ O ₆ with PbO, ZrO ₂ , TiO ₂ and Mn(NO ₃ ) ₂ solution according to the stoichiometric ratio in the chemical formula, Wherein, the mass concentration of Mn(NO ₃ ) ₂ solution is 2%;

(3) Heat the mixture at 800-900°C for 4-6 hours for pre-sintering; after pre-sintering, crush, sieve, preform and form, and then sinter at 1250-1300°C for 2-3 hours, using double crucibles for sintering Sealed atmosphere superimposed firing, so that the sintering process is carried out in a saturated lead atmosphere;

(4) Grinding, cleaning, silvering and firing the sintered material;

(5) Put the material in silicone oil at 100-120°C and apply an electric field of 3-5KV/mm to polarize for 15-30 minutes, then keep the pressure and cool to room temperature.

The PMN-PZT pyroelectric ceramic prepared by the present invention has high pyroelectric coefficient, low dielectric loss and suitable dielectric constant, has good comprehensive pyroelectric performance, and meets the requirements for making pyroelectric infrared detectors . Its performance parameters are shown in Table 1.

Table 1 Performance parameters of zirconium-rich PMN-PZT materials at room temperature F _RL -F _RH phase transition Dielectric constant ε _r 197 300 Dielectric loss tan δ 0.15% 0.45% Pyroelectric coefficient p(C/cm ² ℃) 3.5×10 ^-8 35×10 ^-8 Detection figure of merit F _D (Pa ^-1/2 ) 8.7×10 ^-5 40.5×10 ^-5

Description of drawings

Fig. 1 is the process flow chart of the present invention's preparation pyroelectric ceramic method;

Fig. 2 is the SEM photograph of the natural surface of the PMN-PZT material sintered sample of different manganese content, wherein figure (a) 0at%Mn, figure (b) 1at%Mn, figure (c) 2at%Mn;

Figure 3 is the SEM photographs of the natural surface of PMN-PZT material sintered samples at different sintering temperatures, in which, picture (a) is 1250°C, picture (b) is 1265°C, and picture (c) is 1300°C.

Detailed ways

The steps of the preparation method of the present invention comprise:

1. Using the precursor synthesis process, first use analytically pure MgO and Nb ₂ O ₅ to mix uniformly at a mass ratio of 1:1, and keep warm at 900-1100°C for 4-6 hours to synthesize MgNb ₂ O ₆ .

2. According to the chemical formula Pb _1+d [(Zr _x Ti _1-x ) _1-y (Mg _1/3 Nb _2/3 ) _y ]O ₃ +z at% Mn (wherein, 0.65≤x≤0.95, 0≤ y≤0.3, 0≤d≤0.1, 0≤z≤5), mix the synthesized MgNb ₂ O ₆ with PbO, ZrO ₂ , TiO ₂ and Mn(NO ₃ ) ₂ solutions according to the stoichiometric ratio in the chemical formula. Wherein, the Mn(NO ₃ ) ₂ solution with a mass concentration of 2% is selected for manganese doping. Most of the addition of manganese in the current literature reports is in the solid form of MnCO ₃ , MnO ₂ or Mn(CH ₃ COO) ₂ . The disadvantage is that there will be problems such as the loss of manganese element precipitation and uneven mixing during the mixing and drying process. It will seriously affect the stoichiometric ratio of the final product, thereby affecting the consistency and repeatability of its performance. The present invention selects the Mn(NO ₃ ) ₂ solution with a mass concentration of 2%, which makes the addition of manganese easier and effectively improves the problems of precipitation loss and uneven mixing.

3. The secondary firing process of PZT ceramics is adopted. 800-900°C heat preservation for 4-6 hours pre-calcination; crushing, sieving, forming, the forming process includes two steps of pre-forming and forming to ensure the uniformity and compactness of the sample; 1250-1300°C heat preservation for 2-3 hours for sintering , During sintering, double-crucible sealed atmosphere stacking method is adopted, and PbO powder is mixed (added) into the zirconium powder paved in the small crucible, so that the sintering is carried out in a saturated lead atmosphere, so as to effectively suppress lead volatilization.

4. The sintered sample is ground, cleaned, covered with silver, and fired.

5. Place the sample in silicone oil at 100-120°C and polarize with an electric field of 3-5KV/mm for 15-30 minutes, then keep pressure and cool to room temperature to ensure sufficient polarization.

The basic structural composition of the prepared pyroelectric ceramics is: Pb _1+d [(Zr _x Ti _1-x ) _1-y (Mg _1/3 Nb _2/3 ) _y ]O3+z at% Mn, wherein, 0.65≤x≤0.95, 0≤y≤0.3, 0≤d≤0.1, 0≤z≤5.

The invention summarizes a better formula and preparation process by changing the sintering temperature and manganese doping amount.

Below by concrete example, further illustrate feature and effect of the present invention:

Example 1:

Using the precursor synthesis process, the analytically pure MgO and Nb ₂ O ₅ were mixed uniformly at a mass ratio of 1:1, and MgNb ₂ O ₆ was synthesized at 1000°C for 6 hours. Then, according to the chemical formula Pb _1.01 [(Zr _0.90 Ti _0.10 ) _0.85 (Mg _1/3 Nb _2/3 ) _0.15 ]·O ₃ , use the synthesized MgNb ₂ O ₆ and PbO, ZrO ₂ , TiO ₂ according to the chemical formula in the chemical formula Metering ratio ingredients, after ball milling, crushing, and sieving, adopt the secondary firing process of PZT ceramics, pre-fire at 800°C for 6 hours, and crush, sieve, and shape the pre-fired powder (the molding process includes Two steps of preforming and molding), and then sintering at 1265°C for 2 hours in a sealed atmosphere with double crucibles. Grind the sintered sample, clean it, coat it with silver, and burn the electrode. Then place the sample in silicone oil at 120°C and add a 3KV/mm electric field to polarize for 30 minutes, then keep pressure and cool to room temperature, and test after short-circuiting for 24 hours. Its performance is shown in Table 3.

Example 2-6:

According to the chemical formula Pb _1.01 [(Zr _0.90 Ti _0.10 ) _0.85 (Mg _1/3 Nb _2/3 ) _0.15 ]O ₃ +x at% Mn(NO ₃ ) ₂ ingredients, wherein, the mass concentration of Mn(NO ₃ ) ₂ solution 2%, x=1.0, 2.0, 3.0, 4.0, 5.0, as shown in Table 2. All the other are the same as example 1. Its performance is shown in Table 3.

Table 2 example 2 3 4 5 6 Mn(NO ₃ ) ₂ content (at%) 1.0 2.0 3.0 4.0 5.0

Table 3 Performance parameters of different manganese-doped PMN-PZT pyroelectric materials Mn content (at%) Dielectric constant Dielectric loss Room temperature pyroelectric coefficient p(10 ^-8 C/cm ² ℃) p _max at F _RL -F _RH phase transition temperature (10 ^-8 C/cm ² ℃) 0 355 2.13% 1.3 7 1.0 282 0.60% 1.9 17 2.0 256 0.28% 2.8 29 3.0 197 0.15% 3.5 35 4.0 191 0.20% 2.0 twenty two 5.0 195 0.51% 1.2 11

Example 7-9:

According to the ingredients of Pb _1.01 [(Zr _0.90 Ti _0.10 ) _0.85 (Mg _1/3 Nb _2/3 ) _0.15 ]O ₃ +2at% Mn(NO ₃ ) ₂ , they were sintered at 1250°C, 1265°C, and 1300°C for 2 hours respectively. As in Table 4. All the other are the same as example 1. Its performance is shown in Table 5.

Table 4 example 7 8 9 Sintering temperature (℃) 1250 1265 1300

Table 5 Performance parameters of PMN-PZT pyroelectric materials at different sintering temperatures Sintering temperature (℃) Dielectric constant Dielectric loss Room temperature pyroelectric coefficient p(10 ^-8 C/cm ² ℃) p _max at F _RL -F _RH phase transition temperature (10 ^-8 C/cm ² ℃) 1265 202 0.35% 1.5 18 1275 197 0.23% 2.8 29 1300 223 0.58% 1.2 13

Claims (1)

1, a kind of method for preparing pyroelectric ceramics, its step comprises:

(1) with MgO and Nb ₂O ₅Mix at 1: 1 by mass ratio, at 900～1100 ℃ of insulation 4～6h, synthetic MgNb ₂O ₆

(2) according to chemical formula Pb _1+d[(Zr _xTi _1-x) _1-y(Mg _1/3Nb _2/3) _y] O ₃+ zat%Mn, in the formula, synthetic MgNb is used in 0.65≤x≤0.95,0≤y≤0.3,0≤d≤0.1,0≤z≤5 ₂O ₆With PbO, ZrO ₂, TiO ₂And Mn (NO ₃) ₂The stoichiometric ratio that solution is pressed in the chemical formula is mixed, wherein, and Mn (NO ₃) ₂The mass concentration of solution is 2%;

(3) mixture was carried out pre-burning in 4～6 hours 800～900 ℃ of insulations; Pulverize after the pre-burning, sieve, premolding and moulding, sintering was carried out in 1250～1300 ℃ of insulations in 2～3 hours then, sintering adopts folded burning of two crucibles sealing atmosphere, and sintering process is carried out in saturated plumbous atmosphere;

(4) material behind the sintering is carried out abrasive disc, cleaning, quilt silver and burning electrode;

(5) material is placed in 100～120 ℃ of silicone oil and added 3～5KV/mm electric field polarization 15～30 minutes, pressurize is cooled to room temperature then.

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