A cold sintering assisted preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties

Abstract

The present invention relates to the technical field of multiferroic materials, and in particular to a cold sintering auxiliary preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties: (1) ingredients are prepared according to the correct stoichiometric ratio, ball milled and dried, and sieved to obtain powder; (2) the obtained powder is calcined at high temperature, ball milled and sieved to obtain powder; (3) the obtained powder is added with polyvinyl alcohol (PVA, concentration is 5wt%), and the powder is ground and mixed uniformly; (4) the obtained powder is cold sintered under 500MPa pressure and 180°C to obtain a preliminarily densified ceramic green body; (5) the obtained ceramic green body is heat treated at different temperatures. The sintering temperature of the material can be significantly reduced after the cold sintering treatment, thereby refining the grain size of the ceramic and improving the performance of the composite ceramic.

Description

Technical Field

[0001] The present invention relates to the technical field of multiferroic materials, and in particular to a cold sintering assisted preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties. Background Art

[0002] In recent years, the miniaturization and multifunctionalization of electronic components have driven the rapid development of electronic information technology. Such multifunctional materials have been favored by researchers because they can perform multiple tasks simultaneously. Multiferroic materials have great advantages in this regard. It is expected to achieve magnetic (ferroelectric) data storage controlled by an electric (magnetic) field, thus meeting the growing demand for information density storage and manipulation speed of people today. At the same time, multiferroic materials also have a wide range of application prospects, such as multistate memories, magnetic read / write hard disks, and magnetoelectric sensors.

[0003] BiFeO3 is a multiferroic material with ferroelectric and ferromagnetic orders while having excellent magnetic properties, and has a relatively high Curie temperature and antiferromagnetic Néel temperature. However, BiFeO3 has disadvantages such as high leakage current, large coercive field, and poor magnetic properties. At the same time, the magnetoelectric coupling ability is poor, and its application is also limited. Scientists began to study the A, B-site ion substitution method, mainly to form a stable solid solution of BiFeO3 with other perovskite materials (BaTiO3, CaTiO3, PbTiO3), so as to improve the multiferroic properties of BiFeO3 ceramics. In addition, the intrinsic magnetization intensity of BiFeO3 is weak, and it is difficult to achieve ferroelectric control of magnetic order. Therefore, a ferroelectric phase and a ferromagnetic phase are introduced to form a composite phase system, and coupling is achieved through strain and interface charge transfer. Some studies have shown that BaTiO3 forms a single stable solid solution with BiFeO3, and at the same time, the ferroelectricity and magnetism are also improved, mainly reflected in the obvious reduction of the leakage current density and the increase of the remanent magnetization intensity. Therefore, it is used as the ferroelectric phase. BaFe 12 O 19 Due to its unique structure, it has a relatively high uniaxial magnetocrystalline anisotropy field, high saturation magnetization intensity, wear and corrosion resistance strength, relatively high resistivity, small eddy current loss, low cost, and relatively high Curie temperature. As one of the typical representatives of permanent magnet ferrites, it is very suitable to be selected as the ferromagnetic phase in the composite material.

[0004] During the research process, it was found that the ferroelectric phase (0.75BiFeO3-0.25BaTiO3) and the ferromagnetic phase (BaFe 12 O 19) have significantly different sintering temperatures, which will cause the grain size of the ferroelectric phase with a lower sintering temperature to become larger, which will lead to an increase in the leakage current of the material, which will cause a significant decline in the ferroelectric properties of the material. In April 2019, the 4th issue of the Journal of the European Ceramic Society, Volume 39, pages 986-993 published an article titled "Composition, microstructure and electrical properties of K 0.5 Na 0.5 NbO3 ceramics fabricated by cold sintering assisted sintering". This study shows that the increase in the green density can effectively reduce the sintering temperature and greatly improve the sintering density of the final product. The formation of the K4Nb6O 17 phase and the increase in the sintering density can effectively reduce the evaporation of alkali elements (especially potassium), thereby improving the properties of K 0.5 Na 0.5 NbO3 ceramics. The ceramics sintered at 1115 °C exhibit excellent ferroelectric, piezoelectric and dielectric properties.

[0005] Therefore, on the standard solid-phase sintering, the cold sintering technology is introduced, that is, a technology to achieve ceramic densification with a transient solution as an additive at low temperature (usually below 350 °C) and uniaxial pressure (up to 600 MPa). In the composite system, it can effectively reduce the sintering temperature of the material, reduce the leakage current of the material, and improve the ferroelectric properties.

[0006] As the most significant feature, the low temperature and high pressure in cold sintering greatly reduce the energy consumed for ceramic densification. It has been calculated in the prior art that the cold sintering process can reduce the energy consumption in the sintering process of BaTiO3 powder by two orders of magnitude, from 2800 kJ·g -1 in traditional sintering to 30 kJ·g -1 . In the case of low energy input, the reason why cold sintering can promote the densification of powder is its unique processing method and dynamic environment, resulting in the requirement for the reduction of the Gibbs free energy of the ceramic powder system for densification being lower than that of the traditional high-temperature sintering process.

[0007] When producing the composite ceramic BFO-BTO / BaM, it is found that there are large differences in the grain sizes of the ferroelectric phase and ferromagnetic phase of the material. This difference may lead to a decline in the ferroelectric properties of the composite ceramic. To improve this problem, we need to use the cold sintering process to sinter the composite ceramic to reduce the sintering temperature and refine the grains, so as to obtain a composite ceramic with excellent multiferroic properties. It is of great significance for various application fields. Summary of the Invention

[0008] The present invention aims to solve a problem, that is, how to obtain a composite ceramic material with excellent multiferroic properties by reducing the sintering temperature and refining the grains of the composite ceramic. A cold sintering assisted preparation method for bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties is provided.

[0009] To achieve the above object, the present invention discloses a cold sintering assisted preparation method for bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties, comprising the following steps:

[0010] S1, proportioning: drying the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2, and weighing the dried raw materials according to the stoichiometric ratio;

[0011] S2, primary ball milling: adding deionized water to the raw materials weighed in step S1 for the first ball milling, drying, then grinding, and sieving to obtain uniform powder;

[0012] S3, trial pre-sintering: pre-sintering the powder obtained by sieving in step S2;

[0013] S4, secondary ball milling: grinding the powder pre-sintered in step S3 into powder, adding ball milling beads and deionized water for the second ball milling, drying, sieving, granulating, and sieving again to obtain uniform powder;

[0014] S5, tabletting: performing cold sintering treatment on the powder obtained in step S4 in a mold, and simultaneously performing pressure and heating treatment, and obtaining a cylindrical ceramic green body after the cold sintering treatment;

[0015] S6, annealing: burying the ceramic green body in step S5 with powder of the same composition, and obtaining a ceramic sample after heat preservation.

[0016] The stoichiometric ratio in step S1 is as follows: (1 - x)(0.75BiFeO3 - 0.25BaTiO3) / xBaFe 12 O 19 , where x = 0.075.

[0017] The drying temperature in step S1 is 80 °C, and the drying time is 48 h.

[0018] The ball milling time in step S2 is 24 h, the ball milling rate is 200 r / min, the drying temperature is 80 °C, the drying time is 48 h, and the sieving mesh number is 120 mesh.

[0019] The ball milling time in step S4 is 24 h, the ball milling rate is 200 r / min, the drying temperature is 80 °C, the drying time is 48 h, the sieving mesh number is 120 mesh, and 15% by mass of PVA (with a concentration of 5 wt%) is added during granulation.

[0020] In step S5, the pressing pressure of the mold is 500 MPa, the heating temperature is 180 °C, the heating rate is 15 °C / min, and the heat preservation time is 1.5 or 4.5 h.

[0021] In step S6, the annealing temperature is 800 - 900 °C, the heating rate is 5 °C / min, and the heat preservation time is 4 h.

[0022] The present invention also discloses a bismuth ferrite - barium titanate / barium ferrite composite ceramic prepared by the above - mentioned preparation method.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The composite ceramic obtained by the present invention has a lower sintering temperature compared with the composite ceramic obtained by the traditional sintering method. At 850 °C, it can obtain better ferroelectric properties than the composite ceramic obtained by traditional sintering at 940 °C. When the annealing temperature of the composite ceramic prepared by the method of the present invention is 850 °C, its remanent polarization value (Pr = 27.25 μC / cm 2 ) is higher than the remanent polarization value (Pr = 19.79 μC / cm 2 ) of the composite ceramic obtained by traditional sintering. Compared with the existing technology, the present invention can prepare a (1 - x)(0.75BiFeO3 - 0.25BaTiO3) / xBaFe 12 O 19 composite ceramic with uniform composition, dense structure, fine grains and excellent performance; this preparation method is stable, reliable, has a mature process, is easy to operate, and is suitable for large - scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 SEM pictures of bismuth ferrite - barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Examples 1 - 8, where (a) - (h) correspond to Examples 1 - 8 respectively;

[0026] Figure 2 Average grain size of bismuth ferrite - barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Examples 1 - 8;

[0027] Figure 3 Density pictures of bismuth ferrite - barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Examples 1 - 8;

[0028] Figure 4 Leakage current (LM) curves of bismuth ferrite - barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Examples 1 - 8;

[0029] Figure 5Electric hysteresis loops (DHM) of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Examples 1 to 8. (a) to (h) correspond to Examples 1 to 8 respectively. Detailed implementation manners

[0030] The following further elaborates on the above and additional technical features and advantages of the present invention in conjunction with the accompanying drawings.

[0031] Example 1

[0032] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, and the composition of the ceramic material is: 0.925(0.75BiFeO3 - 0.25BaTiO3) / 0.075BaFe 12 O 19 .

[0033] The specific preparation steps of the ceramic material are as follows:

[0034] Ingredient preparation: Put the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2 (with purity not less than 99%) into an oven for 24 h to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0035] Primary ball milling: Put the weighed raw materials into a nylon pot, add zirconia balls as the ball milling medium and deionized water, and place them on a ball mill for ball milling for 24 h at a rotation speed of 200 r / min.

[0036] Drying and sieving: Pour the ball-milled powder into a drying vessel and place it in an oven. After 48 h, grind the dried raw materials and sieve them through a 120-mesh sieve to obtain uniformly sized powder.

[0037] Pre-sintering: Take a small amount of the sieved powder for pre-sintering. According to the XRD analysis results, select a suitable pre-sintering temperature, and then pour all the powder into a crucible. Among them, 0.75BiFeO3 - 0.25BaTiO3 is kept at 940 °C for 3 h, and BaFe 12 O 19 is kept at 1000 °C for 4 h.

[0038] Secondary ball milling: Pour the pre-sintered powder into a nylon pot containing zirconia balls as the ball milling medium and deionized water respectively, and ball mill for 24 h at a rotation speed of 200 r / min.

[0039] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in an oven for 48 h, and then grind and sieve it through a 120-mesh sieve to obtain uniform particles.

[0040] Granulation and sieving: Add 20 g of sieved powder and 0.3 g of PVA (concentration 5 wt%) and grind, then sieve through a 120-mesh sieve to obtain uniform granules.

[0041] Tabletting: Pour the dried powder into a mold, apply a pressure of 500 MPa, heat to 180 °C, and keep the pressure and temperature for 1.5 h.

[0042] Annealing: Bury the ceramic green body with powder of the same composition, then place it in an oven at 800 °C and keep the temperature for 4 h to obtain a ceramic sample. After crushing and silver coating the obtained ceramic sheet, a sample to be measured is obtained.

[0043] The measured performance results are as follows:

[0044]

[0045] Example 2

[0046] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, the composition of the ceramic material is: 0.925(0.75BiFeO3-0.25BaTiO3) / 0.075BaFe 12 O 19

[0047] The specific preparation steps of the ceramic material are as follows:

[0048] Ingredient preparation: Put the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 (with purity not less than 99%) into an oven for 24 h to remove the moisture in the raw materials, and then weigh according to the correct chemical weighing ratio.

[0049] Primary ball milling: Put the weighed raw materials into a nylon jar, add zirconia balls as ball milling medium and deionized water, place on a ball mill and ball mill for 24 h at a rotation speed of 200 r / min.

[0050] Drying and sieving: Pour the powder after ball milling into a drying vessel, place it in an oven, after 48 h, grind the dried raw materials and sieve through a 120-mesh sieve to obtain a powder with uniform particles.

[0051] Pre-sintering: Take a small amount of the sieved powder for pre-sintering test, select a suitable pre-sintering temperature according to the XRD analysis results, then pour all the powder into a crucible, where 0.75BiFeO3-0.25BaTiO3 powder is kept at 940 °C for 3 h, and BaFe 12 O 19 powder is kept at 1000 °C for 4 h.

[0052] Secondary ball milling: The pre-fired powder materials were respectively poured into nylon jars containing zirconia balls as ball milling media and deionized water, and ball milled for 24 h at a rotational speed of 200 r / min.

[0053] Drying and sieving: The slurry after secondary ball milling was poured into a drying vessel and placed in an oven for 48 h. Then, after grinding, it was sieved through a 120-mesh sieve to obtain uniform particles.

[0054] Granulation and sieving: 0.3 g of PVA (concentration 5 wt%) was added to 20 g of the sieved powder and ground, and then sieved through a 120-mesh sieve to obtain uniform particles.

[0055] Tabletting: The dried powder materials were poured into a mold, and under a pressure of 500 MPa and heated to 180 °C, held for 4.5 h with pressure maintained.

[0056] Annealing: The ceramic green body was buried with powder materials of the same composition, and then placed in an oven at 800 °C and held for 4 h to obtain a ceramic sample. After the obtained ceramic piece was crushed, silver-coated, etc., a sample to be measured was obtained.

[0057] The measured performance results are as follows:

[0058]

[0059] Example 3

[0060] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, the composition of the ceramic material is: 0.925(0.75BiFeO3 - 0.25BaTiO3) / 0.075BaFe 12 O 19 .

[0061] The specific preparation steps of the ceramic material are as follows:

[0062] Ingredient preparation: The raw materials Bi2O3, Fe2O3, BaCO3, TiO2 (with purity not less than 99% for all) were placed in an oven for 24 h to remove the moisture in the raw materials, and then weighed according to the correct chemical weighing ratio.

[0063] Primary ball milling: The weighed raw materials were placed in a nylon jar, zirconia balls as ball milling media and deionized water were added, and ball milled on a ball mill for 24 h at a rotational speed of 200 r / min.

[0064] Drying and sieving: The powder materials after the above ball milling were poured into a drying vessel and placed in an oven. After 48 h, the dried raw materials were ground and then sieved through a 120-mesh sieve to obtain powder materials with uniform particles.

[0065] Pre-sintering: Take a small amount of the sieved powder above for trial pre-sintering. According to the XRD analysis results, select the appropriate pre-sintering temperature, and then pour all the powder into a crucible. Among them, the 0.75BiFeO3-0.25BaTiO3 powder is kept at 940 °C for 3 h, and the BaFe 12 O 19 powder is kept at 1000 °C for 4 h.

[0066] Secondary ball milling: Pour the pre-sintered powder into a nylon jar containing zirconia balls as ball milling medium and deionized water respectively, and ball mill for 24 h at a rotation speed of 200 r / min.

[0067] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in an oven for 48 h, and then grind and sieve it through a 120-mesh sieve to obtain uniform particles.

[0068] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it and then sieve it through a 120-mesh sieve to obtain uniform particles.

[0069] Tabletting: Pour the dried powder above into a mold, heat it to 180 °C under a pressure of 500 MPa and keep the pressure for 1.5 h.

[0070] Annealing: Bury the ceramic green body with powder of the same composition, and then place it at 825 °C for 4 h to obtain a ceramic sample. After crushing, silver plating and other treatments on the obtained ceramic piece, a sample to be measured is obtained.

[0071] The measured performance results are as follows:

[0072]

[0073] Example 4

[0074] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, the composition of the ceramic material is: 0.925(0.75BiFeO3-0.25BaTiO3) / 0.075BaFe 12 O 19

[0075] The specific preparation steps of this ceramic material are as follows:

[0076] Ingredient preparation: Put the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 (the purity of which is not less than 99%) into an oven for 24 h to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0077] Primary ball milling: Put the weighed raw materials into a nylon jar, add zirconia balls as ball milling medium and deionized water, place it on a ball mill and ball mill for 24 h at a rotation speed of 200 r / min.

[0078] Drying and sieving: Pour the powder after ball milling mentioned above into a drying vessel, place it in an oven. After 48 hours, grind the dried raw materials and sieve them through a 120-mesh sieve to obtain a powder with uniform particles.

[0079] Pre-sintering: Take a small amount of the sieved powder for pre-sintering test. According to the XRD analysis results, select an appropriate pre-sintering temperature. Then pour all the powder into a crucible. Among them, the 0.75BiFeO3-0.25BaTiO3 powder is kept at 940 °C for 3 hours, and the BaFe 12 O 19 powder is kept at 1000 °C for 4 hours.

[0080] Second ball milling: Pour the pre-sintered powder into nylon jars containing zirconia balls as ball milling media and deionized water respectively, and ball mill for 24 hours at a rotation speed of 200 r / min.

[0081] Drying and sieving: Pour the slurry after second ball milling into a drying vessel, place it in an oven for 48 hours, then grind and sieve through a 120-mesh sieve to obtain uniform particles.

[0082] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it and then sieve through a 120-mesh sieve to obtain uniform particles.

[0083] Tabletting: Pour the dried powder mentioned above into a mold, apply a pressure of 500 MPa and heat to 180 °C, keep the pressure and temperature for 4.5 hours.

[0084] Annealing: Bury the ceramic green body with powder of the same composition, then place it at 825 °C for 4 hours to obtain a ceramic sample. After crushing and silver plating the obtained ceramic sheet, a sample to be measured is obtained.

[0085] The measured performance results are as follows:

[0086]

[0087] Example 5

[0088] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, the composition of the ceramic material is: 0.925(0.75BiFeO3-0.25BaTiO3) / 0.075BaFe 12 O 19

[0089] The specific preparation steps of this ceramic material are as follows:

[0090] Ingredients: Put the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2 (with a purity of not less than 99%) into an oven for 24 hours to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0091] Primary ball milling: Put the weighed raw materials into a nylon pot, add zirconia balls as the ball milling medium and deionized water, and place it on a ball mill for ball milling for 24 hours at a rotation speed of 200 r / min.

[0092] Drying and sieving: Pour the ball-milled powder into a drying vessel and place it in an oven. After 48 hours, grind the dried raw materials and then sieve them through a 120-mesh sieve to obtain powder with uniform particles.

[0093] Pre-sintering: Take a small amount of the sieved powder for trial pre-sintering. According to the XRD analysis results, select an appropriate pre-sintering temperature, and then pour all the powder into a crucible. Among them, the 0.75BiFeO3 - 0.25BaTiO3 powder is kept at 940 °C for 3 hours, and the BaFe 12 O 19 powder is kept at 1000 °C for 4 hours.

[0094] Secondary ball milling: Pour the pre-sintered powder into a nylon pot filled with zirconia balls as the ball milling medium and deionized water respectively, and ball mill for 24 hours at a rotation speed of 200 r / min.

[0095] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in an oven for 48 hours, and then grind and sieve it through a 120-mesh sieve to obtain uniform particles.

[0096] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it, and then sieve it through a 120-mesh sieve to obtain uniform particles.

[0097] Tabletting: Pour the dried powder into a mold, and under a pressure of 500 MPa and heat it to 180 °C for heat preservation and pressure maintenance for 1.5 hours.

[0098] Annealing: Bury the ceramic green body with powder of the same composition, and then place it in an oven at 850 °C for heat preservation for 4 hours to obtain a ceramic sample. After crushing and silver-plating the obtained ceramic piece, a sample to be measured is obtained.

[0099] The measured performance results are as follows:

[0100]

[0101] Example 6

[0102] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this embodiment, the composition of the ceramic material is: 0.925(0.75BiFeO3-0.25BaTiO3) / 0.075BaFe 12 O 19

[0103] The specific preparation steps of the ceramic material are as follows:

[0104] Ingredient preparation: Put the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2 (with purity not less than 99%) into an oven for 24 h to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0105] Primary ball milling: Put the weighed raw materials into a nylon jar, add zirconia balls as the ball milling medium and deionized water, and place them on a ball mill for ball milling for 24 h at a rotation speed of 200 r / min.

[0106] Drying and sieving: Pour the ball-milled powder into a drying vessel and place it in an oven. After 48 h, grind the dried raw materials and sieve them through a 120-mesh sieve to obtain uniformly sized powder.

[0107] Pre-sintering: Take a small amount of the sieved powder for pre-sintering. According to the XRD analysis results, select an appropriate pre-sintering temperature, and then pour all the powder into a crucible. Among them, the 0.75BiFeO3-0.25BaTiO3 powder is kept at 940 °C for 3 h, and the BaFe 12 O 19 powder is kept at 1000 °C for 4 h.

[0108] Secondary ball milling: Pour the pre-sintered powder into a nylon jar containing zirconia balls as the ball milling medium and deionized water respectively, and ball mill for 24 h at a rotation speed of 200 r / min.

[0109] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in an oven for 48 h, and then grind and sieve it through a 120-mesh sieve to obtain uniform particles.

[0110] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it and then sieve it through a 120-mesh sieve to obtain uniform particles.

[0111] Tabletting: Pour the dried powder into a mold, and under a pressure of 500 MPa and heat it to 180 °C for heat preservation and pressure holding for 4.5 h.

[0112] Annealing: Bury the ceramic green body with powder of the same composition, and then place it in an oven at 850 °C for 4 h to obtain a ceramic sample. After crushing and silver-plating the obtained ceramic piece, a sample to be measured is obtained.

[0113] The measured performance results are as follows:

[0114]

[0115] Example 7

[0116] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example. The composition of the ceramic material is: 0.925(0.75BiFeO3 - 0.25BaTiO3) / 0.075BaFe 12 O 19

[0117] The specific preparation steps of the ceramic material are as follows:

[0118] Batching: Put the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2 (with a purity of not less than 99%) into the oven for 24 h to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0119] Primary ball milling: Put the weighed raw materials into a nylon jar, add zirconia balls as the ball milling medium and deionized water, and place them on the ball mill for ball milling for 24 h at a rotational speed of 200 r / min.

[0120] Drying and sieving: Pour the ball-milled powder into a drying vessel and place it in the oven. After 48 h, grind the dried raw materials and sieve them through a 120-mesh sieve to obtain uniformly sized powder.

[0121] Pre-sintering: Take a small amount of the sieved powder for pre-sintering. According to the XRD analysis results, select the appropriate pre-sintering temperature, and then pour all the powder into a crucible. Among them, the 0.75BiFeO3 - 0.25BaTiO3 powder is kept at 940 °C for 3 h, and the BaFe 12 O 19 powder is kept at 1000 °C for 4 h.

[0122] Secondary ball milling: Pour the pre-sintered powder into a nylon jar containing zirconia balls as the ball milling medium and deionized water respectively, and ball mill for 24 h at a rotational speed of 200 r / min.

[0123] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in the oven for 48 h, and then grind and sieve it through a 120-mesh sieve to obtain uniform particles.

[0124] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it and then sieve it through a 120-mesh sieve to obtain uniform particles.

[0125] Tabletting: Pour the dried powder into a mold, apply a pressure of 500 MPa, heat to 180 °C, and hold the pressure and temperature for 1.5 h.

[0126] Annealing: Bury the ceramic green body with powder of the same composition, then place it in an oven at 900 °C and hold for 4 h to obtain a ceramic sample. After crushing and silver plating the obtained ceramic piece, a sample to be measured is obtained.

[0127] The measured performance results are as follows:

[0128]

[0129] Example 8

[0130] A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties in this example, the composition of the ceramic material is: 0.925(0.75BiFeO3 - 0.25BaTiO3) / 0.075BaFe 12 O 19

[0131] The specific preparation steps of this ceramic material are as follows:

[0132] Ingredient preparation: Put the raw materials Bi2O3, Fe2O3, BaCO3, TiO2 (the purity of which is not less than 99%) into an oven for 24 h to remove the moisture in the raw materials, and then weigh them according to the correct chemical weighing ratio.

[0133] Primary ball milling: Put the weighed raw materials into a nylon pot, add zirconia balls as the ball milling medium and deionized water, and place it on a ball mill for ball milling for 24 h at a rotation speed of 200 r / min.

[0134] Drying and sieving: Pour the powder after ball milling into a drying vessel, place it in an oven, after 48 h, grind the dried raw materials and sieve them through a 120-mesh sieve to obtain a powder with uniform particles.

[0135] Pre-sintering: Take a small amount of the sieved powder for pre-sintering, select a suitable pre-sintering temperature according to the XRD analysis results, and then pour all the powder into a crucible. Among them, the 0.75BiFeO3 - 0.25BaTiO3 powder is held at 940 °C for 3 h, and the BaFe 12 O 19 powder is held at 1000 °C for 4 h.

[0136] Secondary ball milling: Pour the pre-sintered powder into a nylon pot containing zirconia balls as the ball milling medium and deionized water respectively, and ball mill for 24 h at a rotation speed of 200 r / min.

[0137] Drying and sieving: Pour the slurry after secondary ball milling into a drying vessel, place it in an oven for 48 h, then grind it and sieve it through a 120-mesh sieve to obtain uniform particles.

[0138] Granulation and sieving: Add 0.3 g of PVA (concentration 5 wt%) to 20 g of the sieved powder, grind it, and then sieve it through a 120-mesh sieve to obtain uniform particles.

[0139] Tabletting: Pour the dried powder mentioned above into a mold, apply a pressure of 500 MPa, heat it to 180 °C, and keep it under pressure for 4.5 h.

[0140] Annealing: Bury the ceramic green body with powder of the same composition, then place it in an oven at 900 °C and keep it for 4 h to obtain a ceramic sample. After crushing, silver plating, etc. of the obtained ceramic sheet, a sample to be measured is obtained.

[0141] The measured performance results are as follows:

[0142]

[0143] For the bismuth ferrite-barium titanate / barium ferrite composite ceramic sheets in Examples 1-8, through SEM, average grain size, density, LM, and DHM, Figures 1 to 5 , the spectral analysis is as follows:

[0144] Figure 1 are the SEM pictures of the bismuth ferrite-barium titanate / barium ferrite composites in Examples 1-8. Among them, (a) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 1, (b) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 2, (c) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 3, (d) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 4, (e) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 5, (f) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 6, (g) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 7, (h) is the SEM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared in Example 8. It can be seen from the figure that with the decrease of the annealing temperature, the grain size gradually decreases, and the decrease of the grain size helps to improve the ferroelectric properties of the material.

[0145] Figure 2It is a picture of the average grain size of the bismuth ferrite-barium titanate / barium ferrite composite ceramics in Examples 1 to 8. As the annealing temperature increases, the average grain size of the material also gradually increases. This is mainly because cold sintering can reduce the annealing temperature of the material, thereby reducing the grain size of the material.

[0146] Figure 3 It is a picture of the density of the bismuth ferrite-barium titanate / barium ferrite composite ceramics in Examples 1 to 8. As the annealing temperature increases, the density of the material also gradually increases. When the annealing temperature of the material is 900 °C, the density ρ of the material = 6.43 g / cm 3 has reached 96.4% of the density ρ = 6.67 g / cm obtained by traditional sintering. 3

[0147] Figure 4 It is an LM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics in Examples 1 to 8. It can be seen that compared with the traditional solid-phase sintering method, cold sintering can significantly reduce the leakage current of the material. This is because cold sintering can reduce the annealing temperature of the material, thereby refining the grain size of the material.

[0148] Figure 5 It is a DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics in Examples 1 to 8. Among them, (a) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 1, (b) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 2, (c) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 3, (d) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 4, (e) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 5, (f) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 6, (g) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 7, (h) is the DHM picture of the bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties prepared in Example 8. It can be seen from the figure that as the annealing temperature increases, the breakdown field strength and the remanent polarization value of the material gradually increase. Among them, the remanent polarization value Pr of (c) = 38.37 μC / cm 2 , which is mainly caused by the too large leakage current of the material. Among them, the remanent polarization value Pr of (e) = 27.04 μC / cm 2 , which is because the grain size of the material decreases.

[0149] ​The above are only the preferred embodiments of the present invention, which are illustrative rather than restrictive to the present invention. Those skilled in the art understand that many changes, modifications or even equivalents can be made within the spirit and scope defined by the claims of the present invention, but all of them will fall within the protection scope of the present invention.

Claims

1. A method for preparing bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties by cold sintering assistance, characterized in that, It includes the following steps: S1, ingredient preparation: Dry the raw materials Bi2O3, Fe2O3, BaCO3, and TiO2, and weigh the dried raw materials according to the stoichiometric ratio; The stoichiometric ratio is as follows: (1 - x)(0.75BiFeO3 - 0.25BaTiO3) / xBaFe 12 O 19 , where x = 0.075; S2, primary ball milling: Add deionized water to the raw materials weighed in step S1 for the first ball milling, dry, then grind and screen to obtain uniform powder; S3, Trial pre-sintering: Pre-sinter the powder obtained by sieving in step S2, where 0.75BiFeO3-0.25BaTiO3 is kept at 940 °C for 3 h, and BaFe 12 O 19 is kept at 1000 °C for 4 h; S4, secondary ball milling: Grind the pre-sintered powder in step S3 into powder, add ball milling beads and deionized water for the second ball milling, dry, screen, granulate, and screen again to obtain uniform powder; S5, tabletting: Perform cold sintering treatment on the uniform powder obtained in step S4 in a mold. The cold sintering treatment is to perform pressure application and heating simultaneously. After the cold sintering treatment, a cylindrical ceramic green body is obtained; S6, annealing: Bury the ceramic green body in step S5 with powder of the same composition, and obtain a ceramic sample after heat preservation; In step S5, the pressure applied is 500 MPa, the heating temperature is 180 °C, the heating rate is 15 °C / min, and the heat preservation time is 1.5 h; In step S6, the heat preservation temperature is 850 °C.

2. The cold sintering assisted preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties as described in claim 1, wherein, In step S1, the drying temperature is 80 °C and the drying time is 48 h.

3. A cold sintering assisted preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties according to claim 1, characterized in that, In step S2, the ball milling time is 24 h, the ball milling rate is 200 r / min, the drying temperature is 80 °C, the drying time is 48 h, and the screen mesh number is 120 mesh.

4. A cold sintering assisted preparation method of bismuth ferrite-barium titanate / barium ferrite composite ceramics with excellent ferroelectric properties as claimed in claim 1, characterized in that, In step S4, the ball milling time is 24 h, the ball milling rate is 200 r / min, the drying temperature is 80 °C, the drying time is 48 h, the screen mesh number is 120 mesh, and PVA is added during granulation.

5. A bismuth ferrite-barium titanate / barium ferrite composite ceramic with excellent ferroelectric properties prepared by the preparation method according to any one of claims 1 to 4.

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