A method for improving the thermal switch ratio of ferroelectric oxide ceramics

Abstract

The application discloses a method for improving the thermal switch ratio of a ferroelectric oxide ceramic, and comprises the following steps: adjusting the component of the ceramic Pb(Zr 1‑ x Ti x )O3 to make x=0.01-0.09, so that the ceramic has coexisting antiferroelectric phase and ferroelectric phase before polarization; and then applying a direct current field to polarize the ceramic, increasing the difference between the thermal conductivities of the ceramic before and after polarization, and thus improving the thermal switch ratio κ on / κ off Compared with the traditional method for adjusting the thermal switch ratio of an oxide ceramic by only using antiferroelectricity or ferroelectricity, the application does not change the preparation process of the ceramic, does not increase the process complexity, and does not increase the cost, and thus can be applied in actual industrial production.

Description

Technical Field

[0001] This invention relates to a method for improving the thermal switching ratio, and more particularly to a method for improving the thermal switching ratio of ferroelectric oxide ceramics. Background Technology

[0002] Ferroelectric oxide ceramics, such as Pb(Zr,Ti)O3 and BaTiO3, are an important class of functional materials with wide applications in both military and civilian fields. For example, based on the ferroelectric, piezoelectric, and dielectric properties of these materials, various electronic devices for information storage, sensing, and detection can be developed. In recent years, the thermal switching effect (i.e., the thermal conductivity κ after polarization) of these materials has been studied... on Thermal conductivity greater than that before polarization κ off Thermal switch ratio κ on / κ off >1) Researchers have attempted to develop novel devices, such as thermal switches similar to electrical switches, to achieve effective control of heat transfer. However, due to the insulating nature of these materials, the contribution of electrons / holes to thermal conductivity is negligible; therefore, their thermal conductivity mainly originates from the contribution of phonons. Although ferroelectric domains can be tuned by designing ferroelectric oxide ceramics with ferroelectric properties, it is possible to control the thermal conductivity of the ceramic before and after polarization to a certain extent, i.e., to achieve control over the thermal switch ratio κ. on / κ off Regulation, but overall the κ after regulation on / κ off The value remains low, only between 1.1 and 1.2. A small thermal switching ratio remains one of the main bottlenecks in the research and development of new heat transfer control devices. Summary of the Invention

[0003] Objective of the Invention: This invention aims to provide a method for improving the thermal on / off ratio of ferroelectric oxide ceramics. The invention utilizes Pb(Zr) 1-x Ti x Taking O3 as an example, this paper provides a method to obtain low κ by controlling the composition. off Value, high κ on Value, thereby obtaining a high thermal switching ratio κ. on / κ off Methods for ferroelectric oxide ceramics.

[0004] Technical solution: The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to the present invention includes: adjusting the ceramic Pb(Zr) 1-x Ti x The composition of O3 results in x = 0.01–0.09, allowing for the coexistence of antiferroelectric and ferroelectric phases before polarization. This coexistence of different phase structures enhances the scattering of phonons at the phase boundaries, thereby reducing the thermal conductivity of the ceramic before polarization, i.e., reducing κ. offThe numerical value of κ is as follows. For polarized ceramics, the DC electric field applied during the polarization process not only transforms the antiferroelectric phase in the ceramic into the ferroelectric phase, increasing the ferroelectric phase content and reducing the scattering of phonons by phase boundaries, but also causes the ferroelectric domains of all ferroelectric phases in the ceramic to align and grow along the direction of the electric field, thereby reducing the scattering of phonons by ferroelectric domain boundaries. Ultimately, this increases the thermal conductivity of the polarized ceramic, i.e., increases κ. on The numerical value of κ. The two factors mentioned above can significantly increase the difference in thermal conductivity of the ceramic before and after polarization, thereby improving the thermal on / off 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 10-60 minutes.

[0006] Furthermore, Pb(Zr) 1-x Ti x In O3, x = 0.01, 0.03, 0.05, 0.07 or 0.09.

[0007] Furthermore, the Pb(Zr) 1-x Ti x The methods for preparing O3 include:

[0008] (1) According to Pb(Zr) 1-x Ti x The chemical formula of Pb3O4 with x = 0.01 to 0.09 is obtained. Pb3O4, ZrO2 and TiO2 powders are weighed according to the corresponding stoichiometric ratio and mixed evenly by ball milling. The mixed powder is then pre-calcined.

[0009] (2) Press the pre-calcined powder into sheets and sinter them to obtain Pb(Zr) 1-x Ti x O3 ferroelectric oxide ceramics.

[0010] Preferably, in step (1), the temperature is raised from room temperature to 400-500°C and kept at that 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℃-1200℃ and the time is 2-3 hours.

[0012] Preferably, the heating and cooling rates are controlled within 3℃ / minute throughout the entire process.

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

[0014] (1) Before polarization, the ceramic contains coexisting antiferroelectric and ferroelectric phases, which enhances the scattering of phonons at the phase boundaries, thereby reducing the thermal conductivity of the ceramic, i.e., reducing κ. off The applied DC electric field (15–65 kV / cm) during polarization not only induced the antiferroelectric-ferroelectric phase transition, increasing the ferroelectric phase content in the ceramic and reducing phonon scattering at phase boundaries, but also caused the ferroelectric domains of all ferroelectric phases to align and grow along the direction of the electric field, further reducing phonon scattering at ferroelectric domain boundaries. This, in turn, increased the thermal conductivity of the polarized ceramic, i.e., increased the κ value. on The numerical value of κ. The two factors mentioned above can significantly increase the difference in thermal conductivity of the ceramic before and after polarization, thereby improving the thermal on / off ratio κ. on / κ off Thermal switching ratio κ on / κ off The values ​​can reach 1.4 at room temperature (25℃), 1.6 at 40℃, 1.8 at 60℃, 2.1 at 80℃, and 2.2 at 100℃;

[0015] (2) By controlling the composition, the present invention can obtain ceramics in which antiferroelectric and ferroelectric phases coexist, 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. Attached Figure Description

[0016] Figure 1 The Pb(Zr) prepared in Examples 1-5 1-x Ti x X-ray diffraction pattern of O3 ceramic sample before polarization;

[0017] Figure 2 The Pb(Zr) prepared in Examples 1, 3, and 5 are 1-x Ti x Hysteresis loop and current curve of O3 ceramic sample;

[0018] Figure 3 The Pb(Zr) prepared in Example 3 0.95 Ti 0.05 )K of O3 ceramic samples at different temperatures on and κ off ;

[0019] Figure 4 The Pb(Zr) prepared in Example 3 0.95 Ti 0.05 )K of O3 ceramic samples at different temperatures on / κ off . Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0021] Example 1

[0022] Based on the chemical formula Pb(Zr) 1-x Ti x With x = 0.01, weigh 22.9790 g of dried Pb3O4, 12.2001 g of ZrO2, and 0.0807 g of TiO2, place them in a 100 mL ball mill jar equipped with grinding beads, add 30 mL of anhydrous ethanol, and ball mill for 24 hours to mix them evenly. After drying at 80 °C for 4 hours, place the powder in an Al2O3 crucible, cover the crucible with an Al2O3 disc to seal the powder. Place the crucible in a box furnace, raise the temperature from room temperature to 450 °C and hold for 60 minutes, then raise the temperature to the pre-calcination temperature (850 °C) and hold for 2 hours, then lower the temperature to 400 °C, and then cool it to room temperature with the furnace. The entire heating and cooling rate is controlled at 3 °C / min. The obtained powder is ball milled and dried again to obtain powder. Then, a suitable amount of the powder is pressed into thin sheets with a diameter of about 10 mm and a thickness of about 1 mm using a pressure of 15 MPa. After spreading a thin layer of the appropriate powder at the bottom of the Al2O3 crucible, a shaped sheet was placed in the center and covered with the powder. Finally, an Al2O3 disc was placed on top of the crucible to seal the sheet. The sealed crucible was placed in a box furnace and heated from room temperature to 450°C and held for 60 minutes. The temperature was then raised to the sintering temperature (1100°C) and held for 3 hours before being lowered to 400°C. The furnace was then allowed to cool to room temperature. The heating and cooling rates were controlled at 3°C / minute throughout the process. Pb(Zr) was obtained. 1-x Ti x O3 ceramic with x = 0.01 was first polished and plated with electrodes. It was then polarized under a DC electric field of 50 kV / cm for 30 minutes, and the structure and properties of the ceramic before and after polarization were characterized.

[0023] Example 2

[0024] Based on the chemical formula Pb(Zr) 1-x Ti xWith x = 0.03, weigh 22.9790 g of dried Pb3O4, 11.9535 g of ZrO2, and 0.2421 g of TiO2, place them in a 100 mL ball mill jar equipped with grinding beads, add 30 mL of anhydrous ethanol, and ball mill for 24 hours to mix them evenly. After drying at 80 °C for 4 hours, place the powder in an Al2O3 crucible, cover the crucible with an Al2O3 disc to seal the powder. Place the crucible in a box furnace, raise the temperature from room temperature to 450 °C and hold for 60 minutes, then raise the temperature to the pre-calcination temperature (850 °C) and hold for 2 hours, then lower the temperature to 400 °C, and then cool it to room temperature with the furnace. The entire heating and cooling rate is controlled at 3 °C / min. The obtained powder is ball milled and dried again to obtain powder. Then, a suitable amount of the powder is pressed into thin sheets with a diameter of about 10 mm and a thickness of about 1 mm using a pressure of 15 MPa. After spreading a thin layer of the appropriate powder at the bottom of the Al2O3 crucible, a shaped sheet was placed in the center and covered with the powder. Finally, an Al2O3 disc was placed on top of the crucible to seal the sheet. The sealed crucible was placed in a box furnace and heated from room temperature to 450°C and held for 60 minutes. The temperature was then raised to the sintering temperature (1150°C) and held for 2.5 hours before being lowered to 400°C. The furnace was then allowed to cool to room temperature. The heating and cooling rates were controlled at 3°C / minute throughout the process. Pb(Zr) was obtained. 1-x Ti x O3 ceramics with x = 0.03 were first polished and plated with electrodes. They were then polarized for 30 minutes under a DC electric field of 50 kV / cm, and the structure and properties of the ceramics before and after polarization were characterized.

[0025] Example 3

[0026] Based on the chemical formula Pb(Zr) 1-x Ti xWith x = 0.05, weigh 22.9790 g of dried Pb3O4, 11.7071 g of ZrO2, and 0.4034 g of TiO2. Place them in a 100 mL ball mill jar equipped with grinding beads and add 30 mL of anhydrous ethanol. Ball mill for 24 hours to mix thoroughly. After drying at 80 °C for 4 hours, place the powder in an Al2O3 crucible and cover it with an Al2O3 disc to seal the powder. Place the crucible in a box furnace and heat from room temperature to 450 °C for 60 minutes. Then, heat to the pre-calcination temperature (850 °C) and hold for 2 hours, then cool to 400 °C. Subsequently, cool with the furnace to room temperature, with the heating and cooling rate controlled at 3 °C / min throughout. The obtained powder is then ball milled and dried again to obtain a powder. Finally, a suitable amount of the powder is pressed into thin sheets with a diameter of approximately 10 mm and a thickness of approximately 1 mm using a pressure of 15 MPa. After spreading a thin layer of the appropriate powder at the bottom of the Al2O3 crucible, a pre-formed sheet was placed in the center and covered with the powder. Finally, an Al2O3 disc was placed on top of the crucible to seal the sheet. The sealed crucible was then placed in a box furnace and heated from room temperature to 450°C and held for 60 minutes. The temperature was then increased to the sintering temperature (1200°C) and held for 2 hours before being lowered to 400°C. The furnace was then allowed to cool to room temperature. The heating and cooling rates were controlled at 3°C / minute throughout the process. Pb(Zr) was obtained. 1-x Ti x O3 ceramics with x = 0.05 were first polished and plated with electrodes. They were then polarized for 30 minutes under a DC electric field of 50 kV / cm, and the structure and properties of the ceramics before and after polarization were characterized.

[0027] Example 4

[0028] Based on the chemical formula Pb(Zr) 1-x Ti xWith x = 0.07, weigh 22.9790 g of dried Pb3O4, 11.4606 g of ZrO2, and 0.5648 g of TiO2, place them in a 100 mL ball mill jar equipped with grinding beads, add 30 mL of anhydrous ethanol, and ball mill for 24 hours to mix them evenly. After drying at 80 °C for 4 hours, place the powder in an Al2O3 crucible, cover the crucible with an Al2O3 disc to seal the powder. Place the crucible in a box furnace, raise the temperature from room temperature to 450 °C and hold for 60 minutes, then raise the temperature to the pre-calcination temperature (850 °C) and hold for 2 hours, then lower the temperature to 400 °C, and then cool it to room temperature with the furnace. The entire heating and cooling rate is controlled at 3 °C / min. The obtained powder is ball milled and dried again to obtain powder. Then, a suitable amount of the powder is pressed into thin sheets with a diameter of about 10 mm and a thickness of about 1 mm using a pressure of 15 MPa. After spreading a thin layer of the appropriate powder at the bottom of the Al2O3 crucible, a pre-formed sheet was placed in the center and covered with the powder. Finally, an Al2O3 disc was placed on top of the crucible to seal the sheet. The sealed crucible was then placed in a box furnace and heated from room temperature to 450°C and held for 60 minutes. The temperature was then increased to the sintering temperature (1200°C) and held for 2 hours before being lowered to 400°C. The furnace was then allowed to cool to room temperature. The heating and cooling rates were controlled at 3°C / minute throughout the process. Pb(Zr) was obtained. 1-x Ti x O3 ceramics with x = 0.07 were first polished and plated with electrodes. They were then polarized for 30 minutes under a DC electric field of 50 kV / cm, and the structure and properties of the ceramics before and after polarization were characterized.

[0029] Example 5

[0030] Based on the chemical formula Pb(Zr) 1-x Ti x22.9790 g of dried Pb3O4, 11.2141 g of ZrO2, and 0.7262 g of TiO2 were weighed and placed in a 100 mL ball mill jar equipped with grinding beads. 30 mL of anhydrous ethanol was added, and the mixture was ball-milled for 24 hours until homogeneous. After drying at 80 °C for 4 hours, the powder was placed in an Al2O3 crucible and covered with an Al2O3 disc to seal the powder. The crucible was placed in a box furnace and heated from room temperature to 450 °C for 60 minutes. The temperature was then raised to the pre-calcination temperature (850 °C) and held for 2 hours before cooling to 400 °C. The furnace was then cooled to room temperature, with the heating and cooling rates controlled at 3 °C / min throughout. The resulting powder was ball-milled and dried again. Finally, a suitable amount of this powder was pressed into sheets approximately 10 mm in diameter and 1 mm thick using a pressure of 15 MPa. After spreading a thin layer of the appropriate powder at the bottom of the Al2O3 crucible, a shaped sheet was placed in the center and covered with the powder. Finally, an Al2O3 disc was placed on top of the crucible to seal the sheet. The sealed crucible was placed in a box furnace and heated from room temperature to 450°C and held for 60 minutes. The temperature was then raised to the sintering temperature (1150°C) and held for 2.5 hours before being lowered to 400°C. The furnace was then allowed to cool to room temperature. The heating and cooling rates were controlled at 3°C / minute throughout the process. Pb(Zr) was obtained. 1-x Ti x O3 ceramics with x = 0.09 were first polished and plated with electrodes. They were then polarized for 30 minutes under a DC electric field of 50 kV / cm, and the structure and properties of the ceramics before and after polarization were characterized.

[0031] Test results:

[0032] Figure 1 The Pb(Zr) prepared in Examples 1, 2, 3, 4, and 5 1-x Ti x The X-ray diffraction (XRD) spectra of the O3 ceramic samples before polarization are shown. It can be seen that the ceramic of Example 1, i.e., x = 0.01, is mainly composed of the antiferroelectric Pbam phase. With increasing x, the content of the ferroelectric R3c phase gradually increases, as evidenced by the gradual merging of the corresponding split (200) and (002) diffraction peaks into a single peak. In the ceramic of Example 5, the antiferroelectric Pbam phase is significantly reduced, while the ferroelectric R3c phase dominates. This indicates that by controlling the composition (i.e., the x value), oxide ceramics with both antiferroelectric and ferroelectric phases can be obtained.

[0033] Figure 2 The Pb(Zr) prepared in Examples 1, 3, and 5 are 1-x Ti xThe hysteresis loop (PE) and current curve (JE) of the O3 ceramic sample are shown in the figure. It can be seen from the figure that the ceramic of Example 1 has an approximately linear PE curve and its remanent polarization is very small (0.4 μC / cm). 2 This is because the ceramic mainly consists of an antiferroelectric phase, and under the alternating electric field of the PE curve in this test, the minimum electric field required to drive the antiferroelectric-ferroelectric phase transition was not reached. Therefore, it only exhibits a PE curve with a near-linear shape similar to the paraelectric effect, and there is no obvious current peak in the corresponding JE curve. The ceramic of Example 3, on the other hand, exhibits the characteristic of coexistence of antiferroelectric and ferroelectric phases: the remanent polarization is 1.5 μC / cm. 2 There are current peaks corresponding to ferroelectric domain reversal (labeled as peak b) and electric field-driven antiferroelectric-ferroelectric phase transitions (labeled as peaks a and c); the ceramic of Example 5 has PE and JE shapes similar to the ceramic of Example 3, but the remanent polarization is further increased to 4.9 μC / cm. 2 This indicates 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 sample prepared in Example 3 at different temperatures before polarization and after applying a polarization electric field of 50 kV / cm are shown. on and κ off Value. Smaller κ off The value is mainly attributed to the enhanced phonon scattering at the phase boundary between the coexisting antiferroelectric and ferroelectric phases in the ceramic before polarization; as the temperature increases, κ... off The value also gradually decreases because high temperature enhances lattice vibrations, leading to further enhancement of phonon scattering, which greatly reduces κ. off Value. Larger κ on The value is because applying a polarization electric field of 50 kV / cm not only leads to an antiferroelectric-ferroelectric phase transition, increasing the ferroelectric phase content in the ceramic, but also causes the ferroelectric domains in the ferroelectric phase to align and grow along the direction of the electric field, thereby reducing the scattering of phonons by the domain boundaries and increasing the κ value. on value.

[0035] Figure 4 The thermal on / off ratio κ of the ceramic sample prepared in Example 3 before polarization and after applying a polarization electric field of 50 kV / cm is... on / κ off As can be seen, at room temperature (25℃), 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 component of ceramic Pb(Zr 1-x Ti x )O3 to make x=0.01-0.09, so that the ceramic has coexisting antiferroelectric phase and ferroelectric phase before polarization, then applying a direct current field to polarize the ceramic, increasing the difference of the thermal conductivity of the ceramic before and after polarization, thereby improving the thermal switch ratio κ on / κ off ; The applied DC electric field during polarization is 15-65 kV / cm. After applying the DC electric field for polarization, the antiferroelectric phase of the ceramic is induced to transform into the ferroelectric phase, increasing the ferroelectric phase content in the ceramic and causing the ferroelectric domains of all ferroelectric phases to align and grow along the direction of the electric field.

2. 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.

3. 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.

4. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to any one of claims 1-3, characterized in that, The Pb(Zr) 1-x Ti x Methods for preparing O3 include: (1) According to the chemical formula Pb(Zr) 1-x Ti x Pb3O4, ZrO2, and TiO2 powder raw materials with corresponding stoichiometric ratios were weighed and mixed uniformly by ball milling. The mixed powder was then pre-calcined. (2) Press the pre-calcined powder into sheets and sinter to obtain Pb(Zr) 1-x Ti x O3 ferroelectric oxide ceramics.

5. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 4, characterized in that, In step (1), before preheating, the temperature is raised from room temperature to 400-500°C and kept at that temperature for 40-80 minutes.

6. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 4, characterized in that, In step (1), the preheating temperature is 800℃-900℃ and the time is 2-3 hours.

7. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 4, characterized in that, The entire heating and cooling rate is controlled within 3℃ / minute.

8. The method for improving the thermal switching ratio of ferroelectric oxide ceramics according to claim 4, characterized in that, In step (2), the sintering temperature is 1100℃-1200℃ and the time is 2-3 hours.

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