Barium titanate-based ferroelectric ceramic electrocaloric material and preparation method thereof

Abstract

The invention belongs to the field of all-solid-state refrigeration materials, and particularly discloses a barium titanate-based ferroelectric ceramic electrocaloric material and a preparation method thereof. The chemical formula of the ceramic electrocaloric material is Ba1-x (Li0. 5Sm0. 5) xTi1-yZryO3, x is more than 0 and less than or equal to 0.2, and y is more than 0.01 and less than or equal to 0.1. According to the ceramic electrocaloric material, the electrocaloric performance and the temperature stability of the lead-free ferroelectric ceramic material are improved at the same time. The preparation process of the ceramic electrocaloric material is simple and high in repeatability, the lithium element, the samarium element and the zirconium element are subjected to solid solution in the lead-free barium titanate ceramic material at the same time, the solid solution elements enter Ba ion sites and Ti ion sites in crystal lattices of BaTiO3 respectively, the original crystal lattice structure is broken, the relaxation property of the barium titanate material is improved, and the performance of the ceramic electrocaloric material is improved. The material has the characteristics of high electrocaloric performance and wide working temperature area.

Description

Technical Field

[0001] The present invention belongs to the technical field related to all-solid-state refrigeration materials, and more specifically, relates to a barium titanate-based ferroelectric ceramic electrocaloric material and a preparation method thereof. Background Art

[0002] Electrocaloric refrigeration is a new type of solid-state refrigeration technology. Its characteristics of high energy efficiency, zero direct greenhouse gas emissions, and easy miniaturization and integration of equipment make it have broad application prospects in the refrigeration of integrated circuits and devices.

[0003] The temperature change in electrocaloric refrigeration comes from the change in entropy realized by the rotation of the dipoles of the spontaneous polarization of the material under the induction of an electric field. Therefore, ferroelectric ceramic materials with high polarization values are an important research field for electrocaloric refrigeration. Common ferroelectric ceramic materials are divided into two categories: lead-free and lead-containing. Lead-containing ferroelectric ceramics usually have stronger polarization, which also means a higher electrocaloric temperature change. However, lead, as the most common heavy metal in life currently, will not only pollute the environment but also seriously affect human health. In recent years, with the increasingly strict environmental protection regulations, the market demand for lead-free ferroelectric materials has been increasing. Among common lead-free ferroelectric ceramics, barium titanate (BaTiO3) has excellent dielectric and ferroelectric properties, and its preparation process is mature and the cost is low, having the potential for large-scale application, and is regarded as one of the excellent matrix materials for studying the electrocaloric effect.

[0004] However, barium titanate has a relatively high Curie temperature (>120 °C) and a narrow working temperature range, which cannot meet the needs of most current electronic devices and domestic refrigeration. Doping is an important means to regulate the electrocaloric properties of barium titanate ceramics. By doping to adjust the phase structure and domain structure, the electrocaloric strength and working temperature range of barium titanate-based ceramics have been effectively improved. However, many current doping methods often have difficulty achieving a balance between electrocaloric strength and working temperature range. Many systems either only shift the Curie temperature to room temperature, increasing the electrocaloric strength near room temperature, or broaden the working temperature range by increasing the relaxivity, but result in a large loss of electrocaloric strength. Summary of the Invention

[0005] In view of the above defects or improvement requirements of the prior art, the present invention provides a barium titanate-based ferroelectric ceramic electrocaloric material and a preparation method thereof. The chemical formula of the barium titanate-based ferroelectric ceramic electrocaloric material is Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3, 0 < x ≤ 0.2, 0.01 < y ≤ 0.1. This material has the characteristics of both high electrocaloric performance and a wide working temperature range.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a barium titanate-based ferroelectric ceramic electrocaloric material with the chemical formula Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3, where 0 < x ≤ 0.2 and 0.01 < y ≤ 0.1.

[0007] Preferably, in the chemical formula, 0.01 < y ≤ 0.06.

[0008] Preferably, in the chemical formula, x = 0.08 and y = 0.02.

[0009] According to the second aspect of the present invention, there is provided a method for preparing a barium titanate-based ferroelectric ceramic electrocaloric material as described in the first aspect of the present invention, comprising the following steps:

[0010] (1) Weigh raw materials of BaCO3, Li2CO3, Sm2O3, TiO2 and ZrO2 according to the stoichiometric ratio of metal elements in the chemical formula Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3, and perform primary ball milling and mixing to obtain a uniformly mixed powder, where 0 < x ≤ 0.2 and 0.01 < y ≤ 0.1;

[0011] (2) The uniformly mixed powder is made into a ceramic green body through pre-sintering, secondary ball milling, drying, sieving, granulation, dry pressing and cold isostatic pressing;

[0012] (3) The ceramic green body is degassed and sintered to obtain a barium titanate-based ferroelectric ceramic electrocaloric material.

[0013] Preferably, the time for both the primary ball milling and the secondary ball milling is 1 to 24 hours.

[0014] Preferably, in step (2),

[0015] The pre-sintering is specifically: the uniformly mixed powder obtained in step (1) is heated to 800 - 1200 °C at a heating rate of 1 - 10 °C / min in an oxygen, air or nitrogen atmosphere and held for 1 - 10 hours;

[0016] The sieving is specifically: sieving through a 40 - 300 mesh sieve and taking the material under the 40 - 300 mesh sieve.

[0017] Preferably, in step (2),

[0018] The granulation specifically is: mixing a binder with the sieved ceramic powder and granulating; wherein, the mass of the binder in the ceramic powder is 1-20 wt%.

[0019] Preferably, in step (2),

[0020] The pressure for dry pressing is between 1 and 20 MPa, and the pressure is maintained for 1-30 minutes;

[0021] The pressure for cold isostatic pressing is 1-300 MPa, and the time for maintaining the pressure is 1-60 minutes.

[0022] Preferably, in step (3),

[0023] The debinding specifically is: heating the green ceramic body to 400-800 °C at a rate of 1-10 °C / min in an oxygen, air or nitrogen atmosphere and holding for 1-10 hours.

[0024] Preferably, in step (3),

[0025] The sintering specifically is: heating the green ceramic body after debinding to 1000-1350 °C at a rate of 1-10 °C / min in an oxygen, air or nitrogen atmosphere and holding for 1-12 hours.

[0026] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, the following technical advantages are mainly possessed:

[0027] (1) For the barium titanate-based ferroelectric ceramic electrocaloric material of the present invention, by hetero-valently doping Li ions and Sm ions with ionic radii smaller than Ba ions at the A site, a certain lattice distortion is introduced, the phase structure of the matrix is regulated, so that the Curie temperature of the matrix moves towards room temperature. When the value of x is not more than 0.2, it is ensured that the Curie temperature of the matrix is near room temperature. The defect dipoles formed by doping also provide more basal entropy for the electrocaloric effect, improving the electrocaloric strength of the material at room temperature; meanwhile, the present invention selects to introduce the relaxation element Zr at the B site to broaden the working temperature range of the material. Normally, the doping amount at the B site needs to reach more than 0.2 to obtain a more relaxed ferroelectric ceramic. However, on the basis of a large amount of lattice distortion brought about by doping at the A site, a small amount of equivalent doping at the B site greatly improves the relaxation degree of the material and broadens the working temperature range of the material. Thus, the barium titanate-based ferroelectric ceramic electrocaloric material provided by the present invention has both high electrocaloric performance and a wide working temperature range. Compared with the prior art, it does not reduce the polarization due to the introduction of a large amount of relaxation elements, thereby sacrificing the electrocaloric strength, and can still have a large electrocaloric strength in a relatively wide temperature range near room temperature.

[0028] (2) In the chemical formula of the present invention, it is preferably 0.01 < y ≤ 0.06. When both the x value and the y value take relatively large values, due to the too high relaxation degree affecting polarization, the electrocaloric strength will be reduced. Correspondingly, as can be seen from the subsequent Example 3, although when the y value is 0.06, the stability of the material at high temperatures can be ensured, its electrocaloric strength shows a downward trend compared with that of Example 1. Therefore, it is further determined that the smaller amount of B-site equivalent doping in the present invention ≤ 0.06.

[0029] (3) In the chemical formula of the present invention, it is preferably x = 0.08 and y = 0.02. At this time, the electrocaloric material of barium titanate-based ferroelectric ceramics has an electrocaloric temperature change of 2.08 K under the test conditions of 100 kV / cm and 40 °C, and an electrocaloric temperature change of about 2 K is achieved in the range of 20 - 70 °C, and its change rate is lower than ±5%. It has significant advantages in terms of the balance of high electrocaloric performance and wide working temperature range compared with the existing barium titanate-based ferroelectric ceramic electrocaloric materials.

[0030] In summary, the electrocaloric ceramic material of the present invention simultaneously solid-solves lithium element, samarium element and zirconium element in the lead-free barium titanate ceramic material. The solid-solved elements enter the Ba ion site and Ti ion site in the crystal lattice of BaTiO3 respectively, breaking the original crystal lattice structure and increasing the relaxor property of the barium titanate material, so that the material has the characteristics of both high electrocaloric performance and wide working temperature range. Description of the Drawings

[0031] Figure 1 It is the XRD test chart of the ferroelectric ceramic electrocaloric materials exemplified by Comparative Example 3 and Examples 1 - 3 of the present invention.

[0032] Figure 2 It is the dielectric temperature spectrum chart of the ferroelectric ceramic electrocaloric material exemplified by Example 1 of the present invention.

[0033] Figure 3 It is the electrocaloric effect temperature change curve chart of the ferroelectric ceramic electrocaloric materials exemplified by Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention changing with the electric field strength at room temperature.

[0034] Figure 4 It is the electrocaloric effect temperature change curve chart of the ferroelectric ceramic electrocaloric materials exemplified by Examples 1 - 3 and Comparative Examples 1 - 3 of the present invention changing with the temperature. Detailed Embodiments

[0035] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] In the present invention, a barium titanate-based ferroelectric ceramic electrocaloric material is prepared through steps such as batching, primary ball milling, pre-sintering, secondary ball milling, drying, sieving and granulation, forming, debinding, and sintering. Among them, the primary ball milling and secondary ball milling in this method are two ball milling processes at different preparation stages.

[0037] The following is an exemplary description of the preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material provided by the present invention, including the following steps:

[0038] Batching: Weigh and mix commercially available, high-purity (purity above 98.00%) BaCO3, Li2CO3, Sm2O3, TiO2, and ZrO2 according to the stoichiometric ratio of metal elements in Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3 to obtain a uniformly mixed ceramic powder; where 0 < x ≤ 0.2 and 0.01 < y ≤ 0.1.

[0039] Primary ball milling: Ball mill for 1 to 24 hours. For example, the ceramic powder obtained by the above ball milling is uniformly mixed by ball milling, using zirconia balls and absolute ethanol with the same mass as the ceramic powder as the solvent, and ball milling for 1 to 24 hours.

[0040] Pre-sintering: Transfer the dried slurry to an alumina crucible and pre-sinter to obtain a pre-sintered powder; where the atmosphere for pre-sintering is oxygen, air, or nitrogen, raise the temperature at a rate of 1 to 10 °C / min to 800 to 1200 °C, and hold for 1 to 10 hours.

[0041] Secondary ball milling: Perform secondary ball milling on the pre-sintered powder, dry to obtain a powder, and the ball milling conditions are the same as those for primary ball milling.

[0042] Sieving: Pass the powder obtained by secondary ball milling and drying through a 40- to 300-mesh sieve, and take the material under the 40- to 300-mesh sieve.

[0043] Granulation: Mix the binder with the sieved ceramic powder for granulation. For example, add an aqueous PVA solution as the binder to the material under the sieve after sieving for mixing and granulation. The binder is 1 to 20 wt% of the powder mass, and the binder is a 1 to 10 wt% aqueous PVA solution.

[0044] Forming: Dry press the granulated powder through a mold and then perform cold isostatic pressing; where for dry pressing, the pressure is between 1 and 20 MPa, and the pressure is maintained for 1 to 30 minutes; the pressure for cold isostatic pressing is 1 to 300 MPa, and the pressure is maintained for 1 to 60 minutes.

[0045] Debinding: Heat the green ceramic body in an oxygen, air, or nitrogen atmosphere at a rate of 1 - 10 °C / min to 400 - 800 °C and hold for 1 - 10 hours to remove organic substances.

[0046] Sintering: Heat the debound green ceramic body in an oxygen, air, or nitrogen atmosphere at a rate of 1 - 10 °C / min to 1000 - 1350 °C and hold for 1 - 12 hours to obtain a barium titanate-based ferroelectric ceramic electrocaloric material.

[0047] Specifically, the chemical composition of the barium titanate-based ferroelectric ceramic electrocaloric material of the present invention is: Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3, where 0 < x ≤ 0.2 and 0.01 < y ≤ 0.1.

[0048] Preferably, in the chemical formula, 0.01 < y ≤ 0.06.

[0049] The barium titanate-based ferroelectric ceramic electrocaloric material prepared by the present invention has the characteristics of both high electrocaloric performance and a wide operating temperature range, and can be used in the field of thermal management of integrated circuits and devices.

[0050] The following further explains the barium titanate-based ferroelectric ceramic electrocaloric material of the present invention through specific examples.

[0051] Example 1

[0052] Prepare a Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.98 Zr 0.02 O3 ferroelectric ceramic material, including the following steps:

[0053] Step 1: Weigh 0.2 mol of Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.98 Zr 0.02 O3 required raw materials of BaCO3, TiO2, Li2CO3, Sm2O3, and ZrO2, and mix them. Use the wet ball milling process to make all raw materials evenly mixed. The mass ratio of the ball milling medium, anhydrous ethanol, and ball milling material is 5:2:1.5. The ball milling time is 6 hours. The ball milling medium is zirconium balls, and the ball milling solvent is anhydrous ethanol.

[0054] Step 2: After drying the powder evenly ball milled in Step 1, heat it to 1000 °C at a rate of 5 °C / min in an air atmosphere and hold for 4 hours.

[0055] Step 3: Ball mill the materials pre-fired in Step 2 again for 6 hours using the same process.

[0056] Step 4: Dry the ceramic powder in Step 3, sieve it through a 80-mesh sieve, add a binder accounting for 10% of the mass of the ceramic powder. The binder is an aqueous solution of polyvinyl alcohol (PVA) with a mass fraction of 4%, granulate it, and sieve it through an 80-mesh sieve.

[0057] Step 5: Dry-press the ceramic powder in Step 4 through a mold at a pressure of 4 MPa for a holding time of 8 seconds, and then perform cold isostatic pressing at a pressure of 120 MPa for a holding time of 300 seconds to obtain a green ceramic body.

[0058] Step 6: Remove the plasticizer from the green ceramic body obtained in Step 5: Heat it to 600 °C at a rate of 5 °C / min in an air atmosphere and hold for 2 hours.

[0059] Step 7: Sinter the green ceramic body obtained in Step 6 in air: Heat it to 1260 °C at a rate of 3 °C / min and hold for 2 hours, then cool it to room temperature in the furnace to obtain Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.98 Zr 0.02 O3 ferroelectric ceramic material.

[0060] Example 2

[0061] Prepare Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.97 Zr 0.03 O3 ferroelectric ceramic material, including the following steps:

[0062] Step 1: Weigh 0.2 mol of BaCO3, TiO2, Li2CO3, Sm2O3, and ZrO2 raw materials required for Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.97 Zr 0.03 O3 according to the stoichiometric ratio, mix them, and use the wet ball milling process to make all the raw materials evenly mixed. The mass ratio of the ball milling medium, anhydrous ethanol, and ball milling material is 5:2:1.5, the ball milling time is 6 hours, the ball milling medium is zirconia balls, and the ball milling solvent is anhydrous ethanol.

[0063] Step 2: Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08Ti 0.97 Zr 0.03 The green body of Ba(Li 0.5 Sm 0.5 ) 0.08 Ti 0.97 Zr 0.03 O3 ceramic was prepared according to the steps 2-6 in Example 1.

[0064] Step 3: Sinter the green body of ceramic obtained in Step 2 in air: heat it up to 1260 °C at a rate of 3 °C / min and hold for 2 hours, then cool it down to room temperature with the furnace to obtain Ba(Li 0.5 Sm 0.5 ) 0.08 Ti 0.97 Zr 0.03 O3 ferroelectric ceramic material. 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.97 Zr 0.03 O3 ferroelectric ceramic material.

[0065] Example 3

[0066] To prepare Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ferroelectric ceramic material, the following steps are included: 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ferroelectric ceramic material, including the following steps:

[0067] Step 1: Weigh 0.2 mol of raw materials BaCO3, TiO2, Li2CO3, Sm2O3, ZrO2 required for Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 according to the stoichiometric ratio, mix them, and use the wet ball milling process to make all raw materials evenly mixed. The mass ratio of the ball milling medium, anhydrous ethanol, and ball milling material is 5:2:1.5, the ball milling time is 6 hours, the ball milling medium is zirconium balls, and the ball milling solvent is anhydrous ethanol. 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 The green body of Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ceramic was prepared according to the steps 2-6 in Example 1.

[0068] Step 2: Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 The green body of Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ceramic was prepared according to the steps 2-6 in Example 1.

[0069] Step 3: Sinter the green body of ceramic obtained in Step 2 in air: heat it up to 1280 °C at a rate of 3 °C / min and hold for 2 hours, then cool it down to room temperature with the furnace to obtain Ba(Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ferroelectric ceramic material. 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.94 Zr 0.06 O3 ferroelectric ceramic material.

[0070] Comparative Example 1

[0071] Prepare Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.99 Zr 0.01 O3 ferroelectric ceramic material, including the following steps:

[0072] Step 1: Weigh 0.2 mol of Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.99 Zr 0.01 O3 required raw materials BaCO3, TiO2, Li2CO3, Sm2O3, ZrO2 for mixing, and use the wet ball milling process to make all raw materials evenly mixed. The mass ratio of the ball milling medium, anhydrous ethanol, and ball milling material is 5:2:1.5. The ball milling time is 6 hours. The ball milling medium is zirconia balls, and the ball milling solvent is anhydrous ethanol.

[0073] Step 2: The Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.99 Zr 0.01 O3 ceramic green body is prepared according to the steps 2-6 in Example 1.

[0074] Step 3: Sinter the ceramic green body obtained in Step 2 in air: Heat it to 1250 °C at a rate of 3 °C / min and hold for 2 hours, then cool it to room temperature with the furnace to obtain Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.99 Zr 0.01 O3 lead-free electrocaloric ceramic material.

[0075] Comparative Example 2

[0076] Prepare Ba 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.9 Zr 0.1 O3 ferroelectric ceramic material, including the following steps:

[0077] Step 1: Weigh 0.2 mol of Ba 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.9 Zr0.1 The BaCO3, TiO2, Li2CO3, Sm2O3 and ZrO2 raw materials required for O3 are mixed, and all the raw materials are evenly mixed by wet ball milling process. The mass ratio of ball milling medium, anhydrous ethanol and ball milling material is 5:2:1.5, the ball milling time is 6 hours, the ball milling medium is zirconium ball, and the ball milling solvent is anhydrous ethanol.

[0078] Step 2: Ba 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.9 Zr 0.1 The O3 ceramic green body was prepared according to steps 2-6 in Example 1.

[0079] Step 3: Sinter the ceramic green body obtained in step 2 in air: heat up to 1300°C at 3°C / min and keep the temperature for 2 hours, then cool to room temperature to obtain Ba 0.94 (Li 0.5 Sm 0.5 ) 0.06 Ti 0.9 Zr 0.1 O3 ferroelectric ceramic material.

[0080] Comparative Example 3

[0081] Preparation of Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 TiO3 ferroelectric ceramic material, comprising the following steps:

[0082] Step 1: According to the stoichiometric ratio, weigh 0.2 mol of Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 The BaCO3, TiO2, Li2CO3 and Sm2O3 raw materials required for TiO3 are mixed, and all the raw materials are evenly mixed by wet ball milling process. The mass ratio of ball milling medium, anhydrous ethanol and ball milling material is 5:2:1.5, the ball milling time is 6 hours, the ball milling medium is zirconium ball, and the ball milling solvent is anhydrous ethanol.

[0083] Step 2: Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 The TiO3 ceramic green body was prepared according to steps 2-6 in Example 1.

[0084] Step 3: Sinter the ceramic green body obtained in step 2 in air: heat up to 1240°C at 3°C / min and keep the temperature for 2 hours, then cool to room temperature to obtain Ba 0.92(Li 0.5 Sm 0.5 ) 0.08 TiO₃ ferroelectric ceramic materials.

[0085] Result analysis: According to the test results of the samples obtained in Examples 1-3 and Comparative Examples 1-3 Figures 1-4 it can be seen that the lead-free electrocaloric ceramic materials of the present invention have the following characteristics:

[0086] Figure 1 are the XRD test patterns of the ferroelectric ceramic materials in Experimental Examples 1-3 and Comparative Example 3. The test results show that the ferroelectric ceramic materials prepared by the present invention are barium titanate-based ferroelectric ceramic materials and no second phase is generated. With the doping of B-site relaxation elements, the phase structure changes and the tetragonality of the ceramic increases.

[0087] Figure 2 is the dielectric temperature spectrum of the lead-free electrocaloric ceramic material prepared in Example 1. It has a relatively wide dielectric temperature peak near the Curie temperature and frequency dispersion phenomenon, indicating that Experimental Example 1 has strong relaxivity.

[0088] Figure 3 is the electrocaloric effect temperature change curve of the ferroelectric ceramic materials of the comparative examples and examples with the change of electric field strength at room temperature. The test results show that the examples have a large electrocaloric effect temperature change near room temperature. Especially, compared with other examples, Example 1 has a larger electrocaloric effect temperature change and electrocaloric strength near room temperature. Figure 4 is the electrocaloric effect temperature change curve of the ferroelectric ceramic materials of the comparative examples and examples with the change of temperature. The test results show that the doping of B-site relaxation elements does broaden the working temperature range, but excessive B-site doping has an impact on the electrocaloric performance of the material.

[0089] Compared with the existing ceramic component design, the present invention adopts a structural regulation method of simultaneous doping at A and B sites. By using a large amount of lattice distortion introduced by A-site doping and adding a small amount of B-site doping on this basis, the relaxivity of the ceramic is significantly improved, and at the same time, the electrocaloric strength of the ceramic is not weakened due to excessive B-site doping, thus balancing the internal conflict between high electrocaloric strength and high temperature stability. Especially, the preferably selected Ba 0.92 (Li 0.5 Sm 0.5 ) 0.08 Ti 0.98 Zr 0.02 O₃ ferroelectric ceramic materials have an electrocaloric strength greater than 2K mm kV -1 , a working temperature range greater than 50K, and have both high electrocaloric performance and a wide working temperature range under an electric field strength of 100kV cm -1 .

[0090] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the present invention and the scope of equivalent technologies thereof, the present invention also intends to include these modifications and variations. The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the scope of protection is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the scope of protection of the present invention.

Claims

1. A barium titanate-based ferroelectric ceramic electrocaloric material, characterized in that, Its chemical formula is Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1- y Zr y O3, 0 < x ≤ 0.2, 0.01 < y ≤ 0.

1.

2. The barium titanate-based ferroelectric ceramic electrocaloric material according to claim 1, wherein In the described chemical formula, 0.01 < y ≤ 0.

06.

3. The barium titanate-based ferroelectric ceramic electrocaloric material according to claim 1, characterized in that, In the described chemical formula, x = 0.08 and y = 0.

02.

4. A method for preparing a barium titanate-based ferroelectric ceramic electrocaloric material according to any one of claims 1-3, characterized in that, It includes the following steps: (1) According to the chemical formula Ba 1-x (Li 0.5 Sm 0.5 ) x Ti 1-y Zr y O3, weigh the raw materials of BaCO3, Li2CO3, Sm2O3, TiO2 and ZrO2, and perform primary ball milling and mixing to obtain a uniformly mixed powder, where 0 < x ≤ 0.2 and 0.01 < y ≤ 0.1; (2) The uniformly mixed powder is made into a green ceramic body after pre-sintering, secondary ball milling, drying, sieving, granulation, dry pressing and cold isostatic pressing. (3) The green ceramic body is degassed and sintered to obtain a barium titanate-based ferroelectric ceramic electrocaloric material.

5. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, The time for both the first ball milling and the second ball milling is 1 to 24 hours.

6. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, In step (2), The specific pre-sintering is as follows: The uniformly mixed powder obtained in step (1) is heated to 800 - 1200 °C at a heating rate of 1 - 10 °C / min in an oxygen, air or nitrogen atmosphere and held for 1 - 10 hours. The specific sieving is as follows: Sieving through a 40 - 300 mesh sieve and taking the material below the 40 - 300 mesh sieve.

7. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, In step (2), The specific granulation is as follows: The binder is mixed with the sieved ceramic powder for granulation; wherein, the mass of the binder in the ceramic powder is 1 - 20 wt%.

8. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, In step (2), The pressure for dry pressing is between 1 - 20 MPa and the pressure is maintained for 1 - 30 minutes. The pressure for cold isostatic pressing is 1 - 300 MPa and the time for maintaining the pressure is 1 - 60 minutes.

9. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, In step (3), The specific degassing is as follows: The green ceramic body is heated to 400 - 800 °C at a heating rate of 1 - 10 °C / min in an oxygen, air or nitrogen atmosphere and held for 1 - 10 hours.

10. The preparation method of the barium titanate-based ferroelectric ceramic electrocaloric material according to claim 4, characterized in that, In step (3), The specific sintering is as follows: The green ceramic body after degassing is heated to 1000 - 1350 °C at a heating rate of 1 - 10 °C / min in an oxygen, air or nitrogen atmosphere and held for 1 - 12 hours.

Images