Method for improving thermal switch ratio of ferroelectric oxide ceramic

Abstract

The invention discloses a method for improving the thermal switch ratio of ferroelectric oxide ceramic, which comprises the following steps: regulating the components of ceramic Pb (Zr1-xTix) O3 to enable x to be 0.01-0.09, enabling the ceramic to have coexisting antiferroelectric phase and ferroelectric phase before polarization, applying a direct-current electric field to perform polarization treatment on the ceramic, and increasing the difference value of the thermal conductivity of the ceramic before and after polarization, thereby improving the thermal switch ratio kon / koff. Compared with a traditional method for regulating and controlling the thermal switch ratio of the oxide ceramic only through anti-ferroelectricity or ferroelectricity, the method does not change the preparation process of the ceramic, does not increase the process complexity and does not increase the cost, and therefore the method can be applied to actual industrial production.

Description

Technical Field

[0001] The invention relates to a method for improving a thermal switching ratio, in particular to a method for improving a thermal switching ratio of a ferroelectric oxide ceramic. Background Art

[0002] Ferroelectric oxide ceramics such as Pb(Zr,Ti)O 3 、BaTiO 3 It is an important functional material with a wide range of applications in military and civilian fields. For example, based on the ferroelectric, piezoelectric, and dielectric properties of this type of material, various electronic devices for information storage, sensing, and detection can be developed. In recent years, based on the thermal switching effect of this type of material (i.e., the thermal conductivity after polarization, κ on Greater than the thermal conductivity κ before polarization off , thermal switching ratio κ on / κ off >1), people try to develop new devices such as thermal switches similar to electric switches to achieve effective regulation of heat transfer. However, due to the insulating properties of this type of material, the contribution of electrons / holes to thermal conductivity is negligible, so its thermal conductivity mainly comes from the contribution of phonons. Although by designing ferroelectric oxide ceramics with ferroelectric properties, the ferroelectric domain can be regulated, and to a certain extent, the thermal conductivity of ceramics before and after polarization can be regulated, that is, the thermal switch ratio κ can be controlled. on / κ off However, the overall regulation of κ on / κ off The value is still relatively low, only between 1.1 and 1.2. The small thermal switching ratio is still one of the main bottlenecks in the research and development of new heat transfer control devices. Summary of the invention

[0003] Purpose of the invention: The present invention aims to provide a method for improving the thermal switching ratio of ferroelectric oxide ceramics. 1-x Ti x ) 3 As an example, a method for obtaining a low κ off Value, high κ on value, thus obtaining a high thermal switching ratio κ on / κ off Method for preparing ferroelectric oxide ceramics.

[0004] Technical solution: The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to the present invention comprises: regulating the ceramic Pb (Zr 1-x Ti x ) 3The composition of x = 0.01 ~ 0.09, so that it has coexisting antiferroelectric phase and ferroelectric phase before polarization. The coexistence of different phase structures enhances the scattering of phonons by the phase boundary, thereby reducing the thermal conductivity of the ceramic before polarization, that is, reducing κ off For the polarized ceramics, the DC electric field applied during the polarization process not only transforms the antiferroelectric phase in the ceramics into the ferroelectric phase, increases the content of the ferroelectric phase in the ceramics, and reduces the scattering of phonons by the phase boundary, but also makes the ferroelectric domains of all ferroelectric phases in the ceramics oriented and grown along the direction of the electric field, thereby reducing the scattering of phonons by the ferroelectric domain boundary, and ultimately improving the thermal conductivity of the polarized ceramics, that is, increasing κ on The above two factors can significantly increase the difference in thermal conductivity of the ceramic before and after polarization, thereby improving the thermal switch ratio κ on / κ off .

[0005] Furthermore, the DC electric field applied during polarization is 15-65 kV / cm, and the polarization treatment time is 10 to 60 minutes.

[0006] Furthermore, Pb(Zr 1-x Ti x ) 3 Where x = 0.01, 0.03, 0.05, 0.07 or 0.09.

[0007] Furthermore, the Pb(Zr 1-x Ti x ) 3 The preparation method comprises:

[0008] (1) According to Pb(Zr 1-x Ti x ) 3 And x = 0.01 ~ 0.09 chemical formula, Pb 3 O 4 、ZrO 2 、TiO 2 The powders are weighed in the corresponding stoichiometric ratio and mixed evenly by ball milling, and the mixed powders are pre-calcined;

[0009] (2) The pre-sintered powder is pressed into tablets and sintered to obtain Pb(Zr 1-x Ti x ) 3 Ferroelectric oxide ceramics.

[0010] Preferably, in the step (1), the temperature is first raised from room temperature to 400-500° C. and kept at this temperature for 40-80 minutes before pre-firing. The pre-firing temperature is 800-900° C. and the time is 2-3 hours.

[0011] Preferably, in step (2), the sintering temperature is 1100° C.-1200° C., and the sintering time is 2-3 hours.

[0012] Preferably, the heating and cooling rates are controlled within 3°C / min throughout the entire process.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0014] (1) Before polarization, there are coexisting antiferroelectric and ferroelectric phases in the ceramic, which enhances the scattering of phonons by the phase boundary, thereby reducing the thermal conductivity of the ceramic, that is, reducing κ off The DC electric field (15-65 kV / cm) applied during the polarization process not only induces the antiferroelectric-ferroelectric phase transition, increases the content of the ferroelectric phase in the ceramic, and reduces the scattering of phonons by the phase boundary, but also makes the ferroelectric domains of all ferroelectric phases oriented and grown along the direction of the electric field, reducing the scattering of phonons by the ferroelectric domain boundary, thereby increasing the thermal conductivity of the ceramic after polarization, that is, increasing κ on The above two factors can significantly increase the difference in thermal conductivity of the ceramic before and after polarization, thereby improving the thermal switch ratio κ on / κ off ; Thermal switch ratio κ on / κ off The value can reach 1.4 at room temperature (25°C), 1.6 at 40°C, 1.8 at 60°C, 2.1 at 80°C, and 2.2 at 100°C;

[0015] (2) The present invention obtains ceramics in which antiferroelectric phase and ferroelectric phase coexist by controlling the components, which can significantly improve the thermal switching ratio. This simple method provides a very convenient and efficient design idea for controlling the thermal transport properties of ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The Pb(Zr) prepared in Example 1-5 1-x Ti x ) 3 X-ray diffraction spectrum of the ceramic sample before polarization;

[0017] Figure 2 The Pb(Zr) prepared in Examples 1, 3, and 5 1-x Ti x ) 3 Hysteresis loop and current curve of ceramic samples;

[0018] Figure 3 The Pb(Zr) prepared in Example 3 0.95 Ti 0.05 ) 3 κ of ceramic samples at different temperatureson and κ off ;

[0019] Figure 4 The Pb(Zr) prepared in Example 3 0.95 Ti 0.05 ) 3 κ of ceramic samples at different temperatures on / κ off . DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0021] Example 1

[0022] According to the chemical formula Pb(Zr 1-x Ti x ) 3 and x = 0.01, weigh 22.9790 g of dried Pb 3 O 4 , 12.2001 g ZrO 2 , 0.0807 g TiO 2 , put it into a 100 ml ball mill with ball mill beads and add 30 ml of anhydrous ethanol, and ball mill for 24 hours to make it evenly mixed. After drying at 80 ° C for 4 hours, the powder was placed in Al 2 O 3 Crucible, made of Al 2 O 3 The disc is placed on the crucible to seal the powder. The crucible is placed in a box furnace, heated from room temperature to 450°C and kept warm for 60 minutes, then heated to the pre-sintering temperature (850°C) and kept warm for 2 hours before cooling to 400°C, and then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the process. The powder is ball-milled again and dried to obtain powder. Then, an appropriate amount of the powder is pressed into a sheet with a diameter of about 10 mm and a thickness of about 1 mm at a pressure of 15 MPa. 2 O 3 After a thin layer of corresponding powder is spread on the bottom of the crucible, the formed slices are placed in it and covered with corresponding powder. 2 O 3 The disc is placed on the crucible to seal the slice. The crucible sealed with the slice is placed in a box furnace and heated from room temperature to 450°C and kept at this temperature for 60 minutes, then heated to the sintering temperature (1100°C) and kept at this temperature for 3 hours before cooling to 400°C and then cooling to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the whole process. 1-x Ti x ) 3The ceramic with x=0.01 is first polished and plated with electrodes, and then polarized for 30 minutes under a DC electric field of 50 kV / cm, and then the structure and properties of the ceramic before and after polarization are characterized.

[0023] Example 2

[0024] According to the chemical formula Pb(Zr 1-x Ti x ) 3 and x = 0.03, weigh 22.9790 g of dried Pb 3 O 4 , 11.9535 g ZrO 2 , 0.2421 g TiO 2 , put it into a 100 ml ball mill with ball mill beads and add 30 ml of anhydrous ethanol, and ball mill for 24 hours to make it evenly mixed. After drying at 80 ° C for 4 hours, the powder was placed in Al 2 O 3 Crucible, made of Al 2 O 3 The disc is placed on the crucible to seal the powder. The crucible is placed in a box furnace, heated from room temperature to 450°C and kept warm for 60 minutes, then heated to the pre-sintering temperature (850°C) and kept warm for 2 hours before cooling to 400°C, and then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the process. The powder is ball-milled again and dried to obtain powder. Then, an appropriate amount of the powder is pressed into a sheet with a diameter of about 10 mm and a thickness of about 1 mm at a pressure of 15 MPa. 2 O 3 After a thin layer of corresponding powder is spread on the bottom of the crucible, the formed slices are placed in it and covered with corresponding powder. 2 O 3 The disc is placed on the crucible to seal the slice. The crucible sealed with the slice is placed in a box furnace and heated from room temperature to 450°C and kept at this temperature for 60 minutes. Then the temperature is raised to the sintering temperature (1150°C) and kept at this temperature for 2.5 hours before being cooled to 400°C. The temperature is then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute. 1-x Ti x ) 3 The ceramic with x=0.03 is first polished and plated with electrodes, and then polarized for 30 minutes under a DC electric field of 50 kV / cm, and then the structure and properties of the ceramic before and after polarization are characterized.

[0025] Example 3

[0026] According to the chemical formula Pb(Zr 1-x Ti x ) 3and x = 0.05, weigh 22.9790 g of dried Pb 3 O 4 , 11.7071 g ZrO 2 , 0.4034 g TiO 2 , put it into a 100 ml ball mill with ball mill beads and add 30 ml of anhydrous ethanol, and ball mill for 24 hours to make it evenly mixed. After drying at 80 ° C for 4 hours, the powder was placed in Al 2 O 3 Crucible, made of Al 2 O 3 The disc is placed on the crucible to seal the powder. The crucible is placed in a box furnace, heated from room temperature to 450°C and kept warm for 60 minutes, then heated to the pre-sintering temperature (850°C) and kept warm for 2 hours before cooling to 400°C, and then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the process. The powder is ball-milled again and dried to obtain powder. Then, an appropriate amount of the powder is pressed into a sheet with a diameter of about 10 mm and a thickness of about 1 mm at a pressure of 15 MPa. 2 O 3 After a thin layer of corresponding powder is spread on the bottom of the crucible, the formed slices are placed in it and covered with corresponding powder. 2 O 3 The disc is placed on the crucible to seal the slice. The crucible sealed with the slice is placed in a box furnace and heated from room temperature to 450°C and kept at this temperature for 60 minutes. Then the temperature is raised to the sintering temperature (1200°C) and kept at this temperature for 2 hours before being cooled to 400°C. The temperature is then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute. 1-x Ti x ) 3 The ceramic with x=0.05 is first polished and plated with electrodes, and then polarized for 30 minutes under a DC electric field of 50 kV / cm, and then the structure and properties of the ceramic before and after polarization are characterized.

[0027] Example 4

[0028] According to the chemical formula Pb(Zr 1-x Ti x ) 3 and x = 0.07, weigh 22.9790 g of dried Pb 3 O 4 , 11.4606 g ZrO 2 , 0.5648 g TiO 2 , put it into a 100 ml ball mill with ball mill beads and add 30 ml of anhydrous ethanol, and ball mill for 24 hours to make it evenly mixed. After drying at 80 ° C for 4 hours, the powder was placed in Al 2 O3 Crucible, made of Al 2 O 3 The disc is placed on the crucible to seal the powder. The crucible is placed in a box furnace, heated from room temperature to 450°C and kept warm for 60 minutes, then heated to the pre-sintering temperature (850°C) and kept warm for 2 hours before cooling to 400°C, and then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the process. The powder is ball-milled again and dried to obtain powder. Then, an appropriate amount of the powder is pressed into a sheet with a diameter of about 10 mm and a thickness of about 1 mm at a pressure of 15 MPa. 2 O 3 After a thin layer of corresponding powder is spread on the bottom of the crucible, the formed slices are placed in it and covered with corresponding powder. 2 O 3 The disc is placed on the crucible to seal the slice. The crucible sealed with the slice is placed in a box furnace and heated from room temperature to 450°C and kept at this temperature for 60 minutes. Then the temperature is raised to the sintering temperature (1200°C) and kept at this temperature for 2 hours before being cooled to 400°C. The temperature is then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute. 1-x Ti x ) 3 The ceramic with x=0.07 is first polished and plated with electrodes, and then polarized for 30 minutes under a DC electric field of 50 kV / cm, and then the structure and properties of the ceramic before and after polarization are characterized.

[0029] Example 5

[0030] According to the chemical formula Pb(Zr 1-x Ti x ) 3 and x = 0.09, weigh 22.9790 g of dried Pb 3 O 4 , 11.2141 g ZrO 2 , 0.7262 g TiO 2 , put it into a 100 ml ball mill with ball mill beads and add 30 ml of anhydrous ethanol, and ball mill for 24 hours to make it evenly mixed. After drying at 80 ° C for 4 hours, the powder was placed in Al 2 O 3 Crucible, made of Al 2 O 3The disc is placed on the crucible to seal the powder. The crucible is placed in a box furnace, heated from room temperature to 450°C and kept warm for 60 minutes, then heated to the pre-sintering temperature (850°C) and kept warm for 2 hours before cooling to 400°C, and then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute throughout the process. The powder is ball-milled again and dried to obtain powder. Then, an appropriate amount of the powder is pressed into a sheet with a diameter of about 10 mm and a thickness of about 1 mm at a pressure of 15 MPa. 2 O 3 After a thin layer of corresponding powder is spread on the bottom of the crucible, the formed slices are placed in it and covered with corresponding powder. 2 O 3 The disc is placed on the crucible to seal the slice. The crucible sealed with the slice is placed in a box furnace and heated from room temperature to 450°C and kept at this temperature for 60 minutes. Then the temperature is raised to the sintering temperature (1150°C) and kept at this temperature for 2.5 hours before being cooled to 400°C. The temperature is then cooled to room temperature with the furnace. The heating and cooling rate is controlled at 3°C / minute. 1-x Ti x ) 3 The ceramic with x=0.09 is first polished and plated with electrodes, and then polarized for 30 minutes under a DC electric field of 50 kV / cm, and then the structure and properties of the ceramic before and after polarization are characterized.

[0031] Test results:

[0032] Figure 1 The Pb(Zr) prepared in Examples 1, 2, 3, 4, and 5 1-x Ti x ) 3 X-ray diffraction spectra (XRD) of the ceramic samples before polarization. It can be seen that the ceramic of Example 1, i.e., x=0.01, is mainly the antiferroelectric Pbam phase. As x increases, the content of the ferroelectric R3c phase gradually increases, which is manifested by the corresponding split (200) and (002) diffraction peaks gradually merging into a single peak. In the ceramic of Example 5, the antiferroelectric Pbam phase is significantly reduced while the ferroelectric R3c phase is dominant. This shows that by adjusting the composition (i.e., the x value), oxide ceramics in which antiferroelectric and ferroelectric phases coexist can be obtained.

[0033] Figure 2 The Pb(Zr) prepared in Examples 1, 3, and 5 1-x Ti x ) 3 The hysteresis loop (PE) and current curve (JE) of the ceramic sample of Example 1 show that the ceramic of Example 1 has an approximately linear PE curve and its residual polarization is very small (0.4 μC / cm 2). This is because the ceramic is mainly an antiferroelectric phase, and under the alternating electric field of the PE curve of the test, the minimum electric field required to drive the antiferroelectric-ferroelectric phase transition is not reached, so it only shows a PE curve similar to the paraelectric effect and a nearly linear shape, and there is no obvious current peak in the corresponding JE curve; the ceramic of Example 3 shows the coexistence of antiferroelectric and ferroelectric phases: the remanent polarization is 1.5μC / cm 2 , there is a current peak corresponding to the ferroelectric domain switching (marked as peak b) and a current peak of the antiferroelectric-ferroelectric phase transition driven by the electric field (marked as peak a and peak c); the ceramic of Example 5 has a PE and JE shape similar to that of the ceramic of Example 3, but the remanent polarization is further increased to 4.9 μC / cm 2 , indicating that it also has coexisting antiferroelectric and ferroelectric phases, but the content of the ferroelectric phase is relatively high.

[0034] Figure 3 The κ values ​​of the ceramic samples prepared in Example 3 at different temperatures before polarization and after applying a 50 kV / cm polarization electric field are shown in Figure 3. on and κ off The smaller κ off The value is mainly attributed to the enhanced scattering of phonons by the phase boundary of the antiferroelectric phase and the ferroelectric phase coexisting in the ceramic before polarization; with the increase of temperature, κ off The value also gradually decreases. This is because high temperature will enhance the lattice vibration, leading to further enhancement of phonon scattering, thus greatly reducing κ off The larger the κ on The reason for the low value is that when a polarization electric field of 50 kV / cm is applied, it will not only cause an antiferroelectric-ferroelectric phase transition, increasing the content of the ferroelectric phase in the ceramic, but also make the ferroelectric domains in the ferroelectric phase oriented and grow along the direction of the electric field, thereby reducing the scattering of phonons by the domain boundary and increasing κ on value.

[0035] Figure 4 is the thermal switching ratio κ of the ceramic sample prepared in Example 3 before polarization and after applying a polarization electric field of 50 kV / cm on / κ off It can be seen that at room temperature (25°C) κ on / κ off The value is 1.4, κ at 60℃ on / κ off The value is 1.8, κ at 100℃ on / κ off The value is 2.2.

Claims

1. A method for improving the thermal switching ratio of ferroelectric oxide ceramics, characterized in that: The method comprises: regulating the ceramic Pb(Zr 1-x Ti x )O3 composition makes x = 0.01 ~ 0.09, so that it has coexisting antiferroelectric phase and ferroelectric phase before polarization, and then a DC electric field is applied to the ceramic for polarization treatment, which increases the difference in thermal conductivity of the ceramic before and after polarization, thereby improving the thermal switch ratio κ on / κ off .

2. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 1, characterized in that: The DC electric field applied during polarization was 15-65 kV / cm.

3. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 1, characterized in that: The polarization treatment time is 10 to 60 minutes.

4. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 1, characterized in that: After applying direct current electric field polarization, the antiferroelectric phase of the ceramic is induced to transform into a ferroelectric phase, the content of the ferroelectric phase in the ceramic is increased, and the ferroelectric domains of all ferroelectric phases are oriented and grown along the direction of the electric field.

5. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 1, characterized in that: Pb(Zr 1- x Ti x )In O3, x=0.01, 0.03, 0.05, 0.07 or 0.

09.

6. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to any one of claims 1 to 5, characterized in that: The Pb(Zr 1-x Ti x ) The preparation method of O3 includes: (1) According to the chemical formula Pb(Zr 1-x Ti x )O3 and x=0.01-0.09, weighing Pb3O4, ZrO2, and TiO2 powder raw materials of corresponding stoichiometric ratios, mixing the powders uniformly by ball milling, and pre-calcining the mixed powders; (2) The pre-sintered powder is pressed into tablets and sintered to obtain Pb(Zr 1-x Ti x )O3 ferroelectric oxide ceramics.

7. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 6, characterized in that: In the step (1), the temperature is first raised from room temperature to 400-500° C. and kept at this temperature for 40-80 minutes before pre-firing.

8. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 6, characterized in that: In the step (1), the pre-burning temperature is 800° C.-900° C. and the time is 2-3 hours.

9. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 6, characterized in that: The heating and cooling rates were controlled within 3°C / min throughout the whole process.

10. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 6, characterized in that: In the step (2), the sintering temperature is 1100° C.-1200° C. and the sintering time is 2-3 hours.

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