Lead magnesium tungstate-based anti-ferroelectric material and preparation method of multilayer ceramic device of lead magnesium tungstate-based anti-ferroelectric material

Abstract

The invention discloses a lead magnesium tungstate-based antiferroelectric material for solid-state refrigeration, a block thereof and a preparation method of a multilayer ceramic device, and relates to a Pb [(Mg0.5-xB'x) (W0.5-yB ''y)] O3 antiferroelectric material (wherein B'is one or more elements of Ni, Co, Fe and Zn, B ''is one or more elements of Mo, Re and Te, x is equal to 0-0.5, and y is equal to 0-0.5) and a method for preparing powder through a solid-phase method and a method for preparing the multilayer ceramic device through a tape casting method. The material generates large refrigeration enthalpy change in a wide temperature area close to the room temperature, and has excellent refrigeration capacity; the temperature corresponding to a refrigeration electrocaloric effect peak can be regulated and controlled by doping different ions, so that the refrigeration requirements in different temperature ranges are met; the micron-sized dielectric layer in the multilayer ceramic can obtain a high working electric field under a relatively low applied voltage, and sufficiently releases huge enthalpy change for refrigeration, so that excellent refrigeration capacity is realized.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramic materials, specifically relating to a lead magnesium tungstate-based antiferroelectric material and a method for preparing its multilayer ceramic devices. Background Technology

[0002] Refrigeration technology plays a vital role in all aspects of human production and life, including food preservation, air conditioning, pharmaceutical storage, and reliable operation of industrial equipment. However, current refrigeration technology mainly relies on Freon-based mechanical compression, which is energy-intensive, inefficient, and causes significant environmental damage. All-solid-state ferroelectric refrigeration based on the electrocaloric effect offers advantages such as zero emissions, high energy efficiency, easy miniaturization, and low cost, making it the most promising green refrigeration technology.

[0003] In practical refrigeration applications, achieving the largest possible enthalpy change within a specific temperature range is crucial, and the lower the operating temperature (close to or below room temperature), the greater the effect of the refrigeration unit and the broader the market. Electrocaloric refrigeration utilizes ferroelectric / antiferroelectric materials, typically generating maximum enthalpy change at the phase transition temperature. However, in traditional ABO3 materials, due to thermodynamic limitations, the enthalpy change is often positively correlated with the phase transition temperature; that is, the higher the phase transition temperature, the greater the enthalpy change, and the lower the phase transition temperature, the smaller the enthalpy change. Therefore, it is difficult to generate an applicable enthalpy change near room temperature. In complex PbB'... 0.5 B" 0.5 In O3 materials, two heterovalent ions are ordered at the B-sites of the perovskite lattice due to their huge valence difference, resulting in a large enthalpy change even at low to near room temperature, making it a solid-state refrigeration material with great application potential. Among them, PbMg... 0.5 W 0.5 O3 antiferroelectric materials can produce a huge enthalpy change of up to 3.92 J / g near room temperature (36 °C), making them one of the best electrocaloric cooling materials currently available. However, PbMg 0.5 W 0.5 The phase transition temperature of bulk O3 ceramics is slightly higher than room temperature, and the breakdown field strength of bulk ceramics is low, making it impossible to apply a sufficiently large electric field to achieve polarization saturation, thus releasing a large ΔH. To address the issue of PbMg... 0.5 W 0.5 To address the challenges of bulk O3 ceramics and broaden their applications, the phase transition temperature (corresponding to the caloric effect peak) can be controlled by different ion doping methods, thereby expanding its operating temperature range to meet cooling requirements across various temperature zones. Furthermore, multilayer ceramic capacitor structures can be fabricated, where thinner dielectric layers enhance the material's breakdown field strength, resulting in a larger enthalpy change. Summary of the Invention

[0004] To achieve a large enthalpy change in cooling within the near-room temperature range and meet cooling requirements across different temperature ranges, this invention optimizes the electrocaloric properties of lead magnesium tungstate-based ferroelectric ceramics and designs and develops Pb[(Mg 0.5-x B' x (W) 0.5-y B” y [O3 antiferroelectric material, wherein B' is one or more elements selected from Ni, Co, Fe, and Zn, and B” is one or more elements selected from Mo, Re, and Te, x = 0–0.5, y = 0–0.5, and multilayer ceramic devices are prepared by solid-state method to produce powder, ceramic bulk and tape casting method. The sample preparation process is as follows.] Figure 1 .

[0005] The Pb[(Mg)] with excellent calorific value provided by this invention 0.5-x B' x (W) 0.5-y B” y The preparation methods for O3 series products mainly include solid-state method for preparing powders and ceramic blocks, and tape casting method for preparing multilayer ceramic devices. Among them, ceramic blocks and multilayer ceramic devices are further prepared based on powders.

[0006] The solid-state method for preparing powders includes the following steps:

[0007] (1) First, according to Pb[(Mg 0.5-x B' x (W) 0.5-y B” y The required mass of PbO, WO3, MgO, NiO, Co2O3, Fe2O3, ZnO, MoO3, ReO3, and TeO3 raw material powders was calculated using the general formula O3 (x: 0~0.5, y: 0~0.5) with stoichiometric ratios, where PbO powder was in excess by 2~10%. The weighed initial raw material powders were individually placed into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then dried at 80℃, and the dried mixed powder was sieved and then pre-calcined in an alumina crucible at 800~900℃ in air for 4 hours.

[0008] (2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice under the same conditions as above for 24h, and then dry and sieve it again to prepare the pre-calcined powder.

[0009] The solid-state method for preparing bulk ceramics includes the following steps:

[0010] (1) Add 2-5% polyvinyl alcohol (PVA) to the pre-burned powder and mix. Press the mixed powder into a disc with a diameter of 10 mm under a uniaxial pressure of 5-10 MPa. The discharge temperature of the disc is 600℃ and the holding time is 2-6 h. The sintering temperature is 800-1000℃ and the holding time is 2-6 h.

[0011] (2) Grind and polish the sintered ceramic block and silver it for later use.

[0012] The fabrication of multilayer ceramic devices by tape casting includes the following steps:

[0013] (1) Weigh the pre-calcined powder and mix it evenly with polyvinyl butyral (PVB), solvent, dispersant, plasticizer, and homogenizer. The molecular weight of PVB is 60,000 to 300,000. The solvent is p-xylene and alcohol, or methyl ethyl ketone and alcohol, or methyl ethyl ketone and water, or alcohol and toluene, or alcohol and trichloroethylene, or n-acetone and methyl ethyl ketone, or acetone and toluene, or p-xylene and n-acetone. The dispersant is soybean oil, peanut oil, or fish oil. The plasticizer is dibutyl phthalate (DBP), polyethylene glycol (PEG-400), and butyl benzyl phthalate (BBP). The homogenizer is cyclohexanone. Mix it evenly with ethanol, methyl ethyl ketone, red herring oil, polyethylene glycol 400, butyl benzyl phthalate, and polyvinyl butyral solution. Then, tumble the mixed slurry at 300 rpm for 24 hours using a tumbler mill.

[0014] (2) Degas the uniformly mixed slurry and pour it into a casting machine for casting, wherein the casting carrier film is a PET polyester film or a polypropylene casting film.

[0015] (3) The Ag / Pd electrode or Pt electrode template is uniformly brushed onto the cast film using screen printing; the cast layer with Ag / Pd electrode or Pt electrode is stacked and laminated into a multilayer ceramic thick film using a hot press; the temperature of the hot press is 60-100℃ and the pressure is 100-300MPa.

[0016] (4) Place the multilayer thick film after lamination onto a zirconium oxide or alumina plate for adhesive removal.

[0017] (5) Place the degummed raw sheet into a sintering furnace for sintering; further grind and polish the sintered ceramic sample, and silver the end electrode for later use.

[0018] Preferably, in step (1) of the casting method for preparing multilayer ceramic devices, the pre-fired powder is sieved through a 300-mesh sieve to disperse the powder.

[0019] Preferably, the content range of each component in step (1) of the casting method for preparing multilayer ceramic devices is as follows: the ratio of powder: PVB: solvent: dispersant: plasticizer: homogenizer is (100wt%): (3~12wt%): (30~60wt%): (0.5~1.5wt%): (3~8wt%): (0.5~2.0wt%).

[0020] Preferably, in step (2) of the casting method for preparing multilayer ceramic devices, the thickness of the casting carrier film is controlled to be 15-100 μm by controlling the spacing of the casting nozzles of the casting machine.

[0021] Preferably, in step (4) of the casting method for preparing multilayer ceramic devices, the debinding temperature is 400-600℃, the debinding speed is 0.5-2℃ / min, and the holding time is 1-5h.

[0022] Preferably, in step (5) of the casting process for preparing multilayer ceramic devices, the sintering temperature of the green sheet is 900-1100℃, and the holding time is 2-5h.

[0023] The beneficial effects of this invention include: by adopting the above technical solutions, this invention prepares Pb[(Mg)] by solid-state method and casting method. 0.5-x B' x (W) 0.5-y B” y O3 multilayer ceramic devices can generate large enthalpy changes in a wide temperature range near room temperature, exhibiting excellent cooling capabilities. The cooling temperature range can be controlled by different ion doping to meet different cooling needs. The phase transition temperature can be controlled by adjusting the thickness of the effective layer of the multilayer ceramic device, broadening the material's cooling applications in different temperature ranges. The micron-level dielectric layer in the multilayer ceramic achieves a high operating electric field under relatively low applied voltage, fully releasing the huge enthalpy change for cooling. Attached Figure Description

[0024] Figure 1 For the preparation of powders and ceramic bulks by solid-state method and the preparation of Pb[(Mg) by tape casting method 0.5-x B' x (W) 0.5-y B” y )] Schematic diagram of O3 multilayer ceramic device.

[0025] Figure 2 Photographs of ceramic bulk materials prepared by solid-state method and multilayer ceramic devices prepared by tape casting method, wherein (a) is a ceramic bulk sample and (b) is a multilayer ceramic sample.

[0026] Figure 3 This is a SEM cross-sectional image of a multilayer ceramic sample with an effective layer thickness of 15 μm. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, those skilled in the art will understand that this invention is not limited to the accompanying drawings and the following embodiments.

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1:

[0030] (1) Powder preparation by solid-state method includes the following steps:

[0031] S1) First, based on the stoichiometry of the components and the purity of the corresponding raw materials, the required amounts of PbO (25.225 g), WO3 (12.845 g), MgO (2.010 g), and NiO (0.414 g) were calculated. The weighed initial raw material powders were then placed one by one into a nylon ball mill jar. Anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then completely dried at 80°C. The dried mixed powder was then sieved and placed in an alumina crucible for pre-calcination at 840°C in air for 4 hours.

[0032] S2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice for 24h under the same conditions as above, and then dry and sieve it again to prepare the pre-calcined powder.

[0033] (2) Characterization of powder

[0034] The particle size of the powder was characterized using a laser particle size analyzer. The particle size distribution results were: D[3,2]=0.672μm, D[4,3]=1.45μm, Dv(10)=0.263μm, Dv(50)=1.08μm, Dv(90)=1.58μm.

[0035] Example 2

[0036] (1) Ceramic blocks were prepared using the pre-fired powder prepared in Example 1 and tested.

[0037] A certain amount of 2% polyvinyl alcohol (PVA) aqueous solution was added to the pre-fired powder. The mixed powder was pressed into discs with a diameter of 10 mm under a uniaxial pressure of 7 MPa. The debinding temperature of the discs was 600℃, and the holding time was 2 h. The sintering temperature was 970℃, and the holding time was 3 h. The sintered ceramic blocks were then ground, polished, silvered, and tested.

[0038] Figure 2(a) is a photograph of a bulk ceramic sample prepared by the solid-state method. The phase transition temperature of the bulk ceramic was determined to be 32 °C using an impedance analyzer, and its phase transition enthalpy was determined to be 3.21 J / g using a differential scanning calorimeter.

[0039] (2) Multilayer ceramic devices were prepared using the pre-fired powder prepared in Example 1 and tested.

[0040] S1) The pre-calcined powder was sieved through a 300-mesh sieve to disperse it. 40g of the powder was weighed and mixed thoroughly with 11.073g of ethanol, 12.333g of butanone, 0.408g of red herring oil, 0.762g of polyethylene glycol 400, 0.762g of butyl benzyl phthalate, and 2.863g of polyvinyl butyral solution. ZrO2 balls were then added as the ball milling media, and the mixed powder was milled at 300 rpm for 24 hours using a tumbling mill.

[0041] S2) Pour the well-mixed slurry into a beaker and place it on a magnetic stirrer for vacuum degassing; S5) Use PET polyester film as the carrier film for casting, cast the degassed slurry through a casting machine, cut the cast film into square samples through a slicing machine, and evenly brush the Ag / Pd electrode template onto the cast film through screen printing.

[0042] S3) The electrode-bearing cast layers are stacked and laminated into a multilayer thick film with 10 effective layers using a uniaxial hot press at 80°C.

[0043] S4) The obtained multilayer ceramic sample was placed on a zirconia plate, the debinding temperature was 600℃, the debinding rate was 0.5℃ / min, and the temperature was held for 2 hours. Then, it was sintered in an air atmosphere at a temperature of 950℃ for 3 hours.

[0044] S5) The sintered multilayer ceramic sample is ground and polished, and the end electrodes are silvered before testing.

[0045] Figure 2 (b) is a photograph of a multilayer ceramic device. The sample is flat and without warping. Figure 3As shown, the cross-sectional morphology of a multilayer ceramic sample with an effective layer thickness of 15 μm was observed using scanning electron microscopy (SEM), where 1 represents the electrode layer and 2 represents the dielectric layer. The multilayer ceramic sample has alternating stacked dielectric layers and internal electrode layers, with the Ag / Pd internal electrode thickness being 1.5 μm and the effective dielectric layer thickness being 15 μm. The dielectric and electrode layers are densely sintered, with adjacent layers tightly bonded and free of cracks. The phase transition temperature of the multilayer ceramic sample with an effective layer thickness of 15 μm was determined to be 8 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample with an effective layer thickness of 15 μm was measured using differential scanning calorimetry, with a phase transition enthalpy of 3.21 J / g. Under an electric field of 240 kV / cm, a positive electrocaloric adiabatic temperature change of 6.2 K and a negative electrocaloric adiabatic temperature change of -3.5 K were obtained, with a total enthalpy change of 2.91 J / g.

[0046] Example 3

[0047] Multilayer ceramic devices were prepared using the pre-fired powder prepared in Example 1, and the preparation process was the same as in Example 2.

[0048] The effective layer thickness of the multilayer ceramic sample was determined to be 23 μm using SEM, and the phase transition temperature was determined to be 13 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample with an effective layer thickness of 23 μm was measured using differential scanning calorimetry, and the phase transition enthalpy was 3.21 J / g.

[0049] Example 4

[0050] Multilayer ceramic devices were prepared using the pre-fired powder prepared in Example 1, and the preparation process was the same as in Example 2.

[0051] The multilayer ceramic sample with an effective layer thickness of 40 μm was tested using SEM. The phase transition temperature of the multilayer ceramic sample with an effective layer thickness of 40 μm was determined to be 25 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample with an effective layer thickness of 40 μm was measured using differential scanning calorimetry, and the phase transition enthalpy was 3.21 J / g.

[0052] Example 5

[0053] Multilayer ceramic devices were prepared using the pre-fired powder prepared in Example 1, with the specific preparation process being the same as in Example 2.

[0054] Multilayer ceramic samples with an effective layer thickness of 70 μm were tested using SEM. The phase transition temperature of the multilayer ceramic sample with an effective layer thickness of 70 μm was determined to be 30 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample with an effective layer thickness of 70 μm was measured using differential scanning calorimetry, and the phase transition enthalpy was 3.21 J / g.

[0055] Example 6

[0056] (1) Powder preparation by solid-state method includes the following steps:

[0057] S1) The required quantities of raw material powder were calculated using stoichiometry: 25.409 g PbO, 12.679 g WO3, 2.249 g MgO, and 0.161 g MoO3. The weighed initial raw material powders were individually placed into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then completely dried at 80°C. The dried mixed powder was then sieved and pre-calcined at 900°C for 4 hours in an alumina crucible under air atmosphere.

[0058] S2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice for 24h under the same conditions as above, and then dry and sieve it again to prepare the pre-calcined powder.

[0059] (2) The main steps for preparing multilayer ceramic devices by tape casting are as follows:

[0060] S1) The pre-calcined powder was sieved through a 300-mesh sieve to disperse it. Then, 40g of the powder was weighed and mixed evenly with 10.251g of ethanol, 18.411g of butanone, 0.449g of red herring oil, 0.8205g of dibutyl phthalate, 0.8205g of butyl benzyl phthalate, and 3.328g of polyvinyl butyral solution. ZrO2 balls were then added as the ball milling media, and the mixed powder was tumbled at 300 rpm for 24 hours using a tumbler mill.

[0061] S2) Pour the well-mixed slurry into a beaker and place it on a magnetic stirrer to remove bubbles under vacuum.

[0062] S3) PET polyester film is used as the carrier film for casting. The defoamed slurry is cast through a casting machine. The cast film is cut into square samples by a slicing machine. Pt electrode templates are evenly brushed onto the cast film by screen printing. The electrode-bearing cast layers are cross-stacked and laminated into a multi-layer thick film using a uniaxial hot press at 70°C.

[0063] S4) The obtained multilayer ceramic sample was placed on a zirconia plate, the debinding temperature was 600℃, the debinding rate was 0.5℃ / min, and the temperature was maintained for 2h. Then, it was sintered in an air atmosphere at a temperature of 1000℃ for 3h.

[0064] S5) The sintered ceramic sample is ground and polished, and the end electrodes are silvered before testing.

[0065] (3) Testing of multilayer ceramic samples

[0066] The multilayer ceramic sample was analyzed using SEM, and the effective layer thickness was 15 μm. The phase transition temperature of the multilayer ceramic sample was determined to be 25 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample was determined using differential scanning calorimetry, and the phase transition enthalpy was 2.89 J / g.

[0067] Example 7

[0068] (1) The main steps for preparing powder by solid-state method are as follows:

[0069] S1) First, the required stoichiometric ratios were calculated to determine the mass of the raw material powders: 25.288 g of PbO, 12.619 g of WO3, 2.015 g of MgO, 0.415 g of NiO, and 0.160 g of MoO3. The weighed initial raw material powders were then individually placed into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then completely dried at 80°C. The dried mixed powder was then sieved and pre-calcined at 870°C for 4 hours in an alumina crucible under air atmosphere.

[0070] S2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice for 24h under the same conditions as above, and then dry and sieve it again to prepare the pre-calcined powder.

[0071] (2) The main steps for preparing multilayer ceramic devices by tape casting are as follows:

[0072] S1) First, the pre-calcined powder is sieved through a 300-mesh sieve to disperse it. Then, 40g of the powder is weighed and mixed evenly with 17.571g of ethanol, 11.505g of n-acetone, 0.490g of red herring oil, 0.7789g of polyethylene glycol 400, 0.7789g of dibutyl phthalate, and 2.8633g of polyvinyl butyral solution. ZrO2 balls are then added as the ball milling media, and the mixed powder is milled at 300 rpm for 24 hours using a tumbling mill.

[0073] S2) Pour the well-mixed slurry into a beaker and place it on a magnetic stirrer to remove bubbles under vacuum.

[0074] S3) PET polyester film is used as the carrier film for casting. The defoamed slurry is cast through a casting machine. The cast film is cut into square samples by a slicing machine. The Ag / Pd electrode template is evenly brushed onto the cast film by screen printing. The electrode-bearing cast layers are cross-stacked and laminated into a multi-layer thick film using a uniaxial hot press at 60°C.

[0075] S4) The obtained multilayer ceramic sample was placed on a zirconia plate, the debinding temperature was 600℃, the debinding rate was 0.5℃ / min, and the temperature was held for 2 hours. Then, it was sintered in air atmosphere at a temperature of 970℃ for 3 hours.

[0076] S5) The sintered multilayer ceramic sample is ground and polished, and the end electrodes are silvered before testing.

[0077] (3) Testing of multilayer ceramic samples

[0078] Multilayer ceramic samples were tested using SEM, with an effective layer thickness of 15 μm. The heat flow curves of the multilayer ceramic samples were measured using differential scanning calorimetry, with a phase transition temperature of 16 °C and a phase transition enthalpy of 2.51 J / g.

[0079] Example 8

[0080] (1) The main steps for preparing powder by solid-state method are as follows:

[0081] S1) First, the required stoichiometric ratios were calculated to determine the mass of the raw material powder: 23.9760 g of PbO, 12.2084 g of WO3, and 4.2857 g of ZnO. The weighed initial raw material powders were then individually placed into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then completely dried at 80°C. The dried mixed powder was then sieved and pre-calcined at 830°C for 4 hours in an alumina crucible under air atmosphere.

[0082] S2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice for 24h under the same conditions as above, and then dry and sieve it again to prepare the pre-calcined powder.

[0083] (2) The main steps for preparing multilayer ceramic devices by tape casting are as follows:

[0084] S1) First, the pre-calcined powder is sieved through a 300-mesh sieve to disperse it. Then, 40g of the powder, 18.571g of ethanol, 10.505g of n-acetone, 0.480g of peanut oil, 0.6889g of polyethylene glycol 400, 0.7889g of butyl benzyl phthalate, and 2.9733g of polyvinyl butyral solution are weighed and mixed evenly. ZrO2 balls are then added as the ball milling media, and the mixed powder is milled at 300 rpm for 24 hours using a tumbling mill.

[0085] S2) Pour the well-mixed slurry into a beaker and place it on a magnetic stirrer to remove bubbles under vacuum.

[0086] S3) PET polyester film is used as the carrier film for casting. The defoamed slurry is cast through a casting machine. The cast film is cut into square samples by a slicing machine. The Ag / Pd electrode template is evenly brushed onto the cast film by screen printing. The electrode-bearing cast layers are cross-stacked and laminated into a multi-layer thick film using a uniaxial hot press at 70°C.

[0087] S4) The obtained multilayer ceramic sample was placed on a zirconia plate, the debinding temperature was 600℃, the debinding rate was 0.5℃ / min, and the temperature was held for 2 hours. Then, it was sintered in air atmosphere at a temperature of 970℃ for 3 hours.

[0088] S5) The sintered multilayer ceramic sample is ground and polished, and the end electrodes are silvered before testing.

[0089] (3) Testing of multilayer ceramic samples

[0090] The multilayer ceramic sample was analyzed using SEM, and the effective layer thickness was 15 μm. The phase transition temperature of the multilayer ceramic sample was determined to be 75 °C using impedance analysis. The heat flow curve of the multilayer ceramic sample was determined using differential scanning calorimetry, and the phase transition enthalpy was 2.15 J / g.

[0091] Comparative Example

[0092] (1) The main steps for preparing powder and bulk ceramics by solid-state method are as follows:

[0093] S1) First, the required stoichiometric ratios were calculated to determine the mass of the raw material powder: 25.3469 g of PbO, 12.9064 g of WO3, and 2.2436 g of MgO. The weighed initial raw material powders were then individually placed into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls were added as milling media. The mixed powder was milled at 300 rpm for 24 hours using a tumbler mill. The thoroughly mixed slurry was then completely dried at 80°C. The dried mixed powder was then sieved and pre-calcined at 850°C for 4 hours in an alumina crucible under air atmosphere.

[0094] S2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder again for 24h under the same conditions as above, and then dry and sieve it again to prepare the pre-calcined powder.

[0095] S3) A certain amount of 2% polyvinyl alcohol (PVA) aqueous solution was added to the pre-fired powder. The mixed powder was pressed into discs with a diameter of 10 mm under a uniaxial pressure of 7 MPa. The debinding temperature of the discs was 600℃, and the holding time was 2 h. The sintering temperature was 950℃, and the holding time was 3 h. The sintered ceramic blocks were then ground, polished, silvered, and tested.

[0096] (2) Testing of bulk ceramics

[0097] The phase transition temperature of the bulk ceramic was determined to be 36℃ using an impedance analyzer. The heat flow profile of the bulk ceramic was measured using a differential scanning calorimeter, and the phase transition enthalpy was 3.92 J / g. However, PbMg... 0.5 W 0.5 O3 bulk ceramics have a low breakdown field strength of only 120 kV / cm, which cannot reach polarization saturation and therefore cannot release a large ΔH.

[0098] Discussion of Results:

[0099] In traditional ABO3 materials, due to thermodynamic limitations, the enthalpy change is often positively correlated with the phase transition temperature; that is, the higher the phase transition temperature, the greater the enthalpy change, and the lower the phase transition temperature, the smaller the enthalpy change. Therefore, it is difficult to generate an applicable enthalpy change for refrigeration at near-room temperature. Researchers commonly use ion substitution to control the phase transition temperature. However, it remains difficult to obtain a large enthalpy change at or below room temperature. Statistical analysis of numerous research results shows that lowering the Curie temperature through ion substitution always comes at the cost of sacrificing the phase transition enthalpy. The embodiments of this application effectively control the phase transition temperature of a multilayer ceramic device by adjusting the effective layer thickness, while maintaining a constant phase transition enthalpy. As shown in the results of Examples 2-5 (see Table 1), the effective layer thickness of the multilayer ceramic device varies within the range of 15–70 μm, allowing for a controllable phase transition temperature range of 8–30 °C, while maintaining the phase transition enthalpy at 3.21 J / g. This method not only fills the gap in low-temperature refrigeration but also offers a simpler and faster method for controlling the effective layer thickness of multilayer ceramic devices compared to ion substitution.

[0100] Table 1. Relationship between phase transition temperature, phase transition enthalpy, and effective layer thickness for devices in Examples 2-5.

[0101] Example Effective layer thickness (μm) Phase transition temperature (°C) Phase transition enthalpy (J / g) 2 15 8 3.21 3 23 13 3.21 4 40 25 3.21 5 70 30 3.21

[0102] This application selects PbMg, which has great application potential. 0.5 W 0.5 O3 antiferroelectric materials exhibit a large enthalpy change of up to 3.92 J / g near room temperature (36 °C). However, PbMg 0.5 W 0.5The phase transition temperature of bulk O3 ceramics is slightly higher than room temperature, and the breakdown field strength of bulk ceramics is low, making it impossible to apply a sufficiently large electric field to achieve polarization saturation, thus releasing a large ΔH. Therefore, the inventors of this invention have controlled the phase transition temperature of the material to room temperature and below by screening ions and combining ion substitution with the preparation of multilayer ceramic devices, thus preparing a material with excellent electrocaloric performance for cryogenic refrigeration. Comparison of the results of Examples 2, 6, and 7 with the comparative examples shows that by screening suitable elements for A-site doping, B-site doping, and A / B-site co-doping, the phase transition temperature of the material can be controlled to 8°C, 16°C, and 25°C, respectively. Furthermore, to meet the refrigeration requirements of different temperature ranges, suitable elements can be screened for doping with Pb and Mg. 0.5 W 0.5 O3 antiferroelectric materials have broadened their operating temperature range. As shown in the results of Examples 2-8, by selecting suitable elements for A-site doping, B-site doping, and A / B-site co-doping, the phase transition temperature of the material can be controlled within the range of 8-75℃, while still maintaining excellent phase transition enthalpy (2.15-3.21 J / g).

[0103] Table 2 Examples 2, 6-8 and Comparative Examples

[0104]

[0105] The foregoing has provided a detailed description of a method for preparing lead magnesium tungstate-based antiferroelectric materials and multilayer ceramic devices for solid-state refrigeration, as well as a preferred embodiment of this application. The description of the preferred embodiments is merely to aid in understanding the method and core concepts of this application. It should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the above teachings or related technical or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing a lead magnesium tungstate-based antiferroelectric material, comprising the following steps: (1) Based on the chemical formula Pb[(Mg 0.5-x B' x (W) 0.5-y B” y [O3], where x: 0~0.5, y: 0~0.5, B' is one or more elements selected from Ni, Co, Fe, and Zn, and B” is one or more elements selected from Mo, Re, and Te. The required mass of raw material powder is calculated by stoichiometry, with PbO powder in excess by 2~10%. The weighed initial raw material powder is placed one by one into a nylon ball mill jar, and anhydrous ethanol and ZrO2 balls are added as ball milling media. The mixed powder is milled at 300 rpm for 24 hours using a tumbler mill. The fully mixed slurry is taken out and thoroughly dried at 80℃. The dried mixed powder is then sieved and placed in an alumina crucible for pre-calcination in an air atmosphere. (2) Add 0.2wt% MnO2 powder to the pre-calcined powder, then roll the mixed powder twice under the same conditions for 24h, and then dry and sieve it again to prepare lead magnesium tungstate-based antiferroelectric material, i.e., pre-calcined powder.

2. A method for preparing lead magnesium tungstate-based antiferroelectric material bulk, characterized in that, The method includes: (1) Add 2-5% polyvinyl alcohol (PVA) to the pre-fired powder and mix. Press the mixed powder into a disc with a diameter of 10 mm under a uniaxial pressure of 5-10 MPa. The discharge temperature of the disc is 600℃ and the holding time is 2-6 h. The sintering temperature is 800-1000℃ and the holding time is 2-6 h. (2) Grind and polish the sintered ceramic block, and silver the end electrodes for later use.

3. A method for preparing multilayer ceramic devices based on lead magnesium tungstate antiferroelectric materials, characterized in that, The method includes: (1) The pre-calcined powder is sieved through a 300-mesh sieve to disperse the powder. The pre-calcined powder is weighed and mixed with PVB, solvent, dispersant, plasticizer and homogenizer, etc., and mixed evenly. The molecular weight of PVB is 60,000 to 300,000. The solvent is p-xylene and alcohol, or methyl ethyl ketone and alcohol, or methyl ethyl ketone and water, or alcohol and toluene, or alcohol and trichloroethylene, or n-acetone and methyl ethyl ketone, or acetone and toluene, or p-xylene and n-acetone. The dispersant is soybean oil, or peanut oil or fish oil. The plasticizer is dibutyl phthalate (DBP), polyethylene glycol (PEG-400) and butyl benzyl phthalate (BBP). The homogenizer is cyclohexanone. (2) Degas the uniformly mixed slurry and pour it into a casting machine for casting, wherein the casting carrier film is a PET polyester film or a polypropylene casting film. (3) Use screen printing to uniformly brush the Ag / Pd electrode or Pt electrode template onto the cast film; use a hot press to stack and laminate the cast layers with Ag / Pd electrode or Pt electrode into a multilayer ceramic thick film. (4) Place the multilayer thick film after lamination onto a zirconium oxide or alumina plate for adhesive removal. (5) The raw sheet after debinding is placed into a sintering furnace for sintering; the sintered ceramic sample is further ground and polished, and the end electrode is silvered.

4. The method according to claim 1, characterized in that, The preheating temperature in step (1) is 800-1100℃, and the holding time is 1-5h.

5. The method according to claim 3, characterized in that, In step (1), the proportions of each component are as follows: pre-calcined powder: PVB: solvent: dispersant: plasticizer: homogenizer (100 wt%): (3-12 wt%): (30-60 wt%): (0.5-1.5 wt%): (3-8 wt%): (0.5-2.0 wt%).

6. The method according to claim 3, characterized in that, The thickness of the cast carrier film in step (2) is 15-100 μm.

7. The method according to claim 3, characterized in that, In step (3), the temperature of the hot press is 60-100℃ and the pressure is 100-300MPa.

8. The method according to claim 3, characterized in that, In step (4), the glue discharge temperature is 400-600℃, the glue discharge speed is 0.5-2℃ / min, and the heat preservation time is 1-5h.

9. The method according to claim 3, characterized in that, The sintering temperature of the green sheet in step (5) is 900-1100℃, and the holding time is 2-5h.

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