A lu, ta simultaneously donor doped strontium titanate-based giant dielectric ceramic material and a preparation method thereof

Abstract

The application relates to the technical field of electronic functional materials, and provides a Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material and a preparation method thereof. The Lu and Ta are simultaneously donor-doped at A (Sr) sites and B (Ti) sites of SrTiO3 respectively, and a nitrogen sintering mode is combined, so that the Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material is obtained through a solid phase synthesis method. The ceramic material has a giant dielectric effect, small dielectric loss, good frequency and temperature stability of dielectric constant, and meets the demand of electronic components miniaturization and energy storage devices on dielectric materials. In the application, the dosages of the dopants Ta2O5 and Lu2O3 are small, and the production cost can be reduced. The preparation method is simple, has good repeatability, high product yield, low cost and is convenient for commercial production.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic functional materials, and in particular to a strontium titanate-based giant dielectric ceramic material doped with Lu and Ta as donors and a preparation method thereof. Background Art

[0002] Giant dielectric ceramics are widely used in the miniaturization of electronic devices. Common giant dielectric ceramics include TiO2-based, NiO-based, CaCu3Ti4O 12 Based on, BaTiO3 based and SrTiO3 based ceramics. Although these ceramic materials have been widely studied and reported, their applications are affected by the defects of the materials themselves. For example, the application of TiO2 based ceramics is limited by its low breakdown strength (5-10kV / mm); NiO based ceramics and CaCu3Ti4O 12 BaTiO3-based ceramics are limited by the difficulty in reducing dielectric loss (>0.1); BaTiO3-based ceramics undergo a ferroelectric phase transition at the Curie temperature (~125°C), causing their dielectric constant to increase sharply to ~10,000, which affects their application under high-temperature conditions. Compared with the above ceramics, SrTiO3-based ceramics have attracted attention due to their advantages such as high breakdown strength (~25kV / mm), low dielectric loss (~0.005), and low frequency and temperature dependence. However, pure SrTiO3 has the problem of a low intrinsic dielectric constant (~300). Therefore, improving the dielectric properties of SrTiO3-based ceramics has extremely important application significance.

[0003] Doping modification and sintering in a non-oxidizing atmosphere can effectively improve the dielectric constant of SrTiO3-based giant dielectric ceramics. For example, Wang et al. (ZJ Wang, MH Cao, ZHY Cao, Q. Zhang, Z. Song, W. Hu, Q. Xu, H. Hao, HX Liu, ZY Yu, Giant permittivity and low dielectric loss of SrTiO3 ceramics sintered in nitrogen atmosphere, J. Eur. Ceram. Soc. 34 (2014) 1755-1760.) reported that pure SrTiO3 ceramics sintered in a nitrogen atmosphere have a giant dielectric constant (ε r ~47601) and low dielectric loss (tanδ~0.0058). Its dielectric constant shows a plateau in the range of -100~200℃, which indicates that the dielectric constant has good temperature stability. The giant dielectric effect and the defect dipole clusters generated by the complete ionization of oxygen vacancies Related. Doping modification also helps to improve the dielectric properties of SrTiO3. Especially for SrTiO3 with ABO3 cubic perovskite structure, ion doping modification at different sites will affect the type of defects, thereby affecting its dielectric properties. Qiao et al. (QiaoY, Li W, Zhang Y, et al. Hole-pinned defect-dipoles induced colossal permittivity in Bi dopedSrTiO3ceramics with Sr deficiency[J]. Journal of Materials Science&Technology, 2020, 44: 54-61.) prepared Sr by A-site doping. 1-1.5x Bi x TiO3 (x = 0, 0.01, 0.05 and 0.1) ceramics can obtain giant dielectric effect when sintered in air atmosphere. When x = 0.05, the ceramic obtains ε r ~10 4 The giant dielectric constant and low dielectric loss of tanδ<0.05. Phase structure analysis and density functional theory calculations show that the free electron pinning effect Defect clusters are the main reason for the giant dielectric effect. Guo et al. (Guo X, Pu Y, Wang W, et al. Colossal permittivity and low dielectric loss in Ta dopedstrontium titanate ceramics by designing defect chemistry [J]. Journal of Alloys and Compounds, 2020, 818: 152866.) prepared SrTi by using Ta element donor doping at the B site. 1-x Ta x O3 ceramics (0.000≤x≤0.014) ceramics. The results show that in the ceramic sample with x=0.010, giant dielectric constant (ε r The improved dielectric performance is related to the electron pinning defect dipole (EPDD) effect, which enhances local polarization and thus increases the dielectric constant. This effect also suppresses long-range electron displacement, thereby reducing dielectric loss over a wide frequency range.

[0004] However, the above studies are all single-element doping modifications, which have limited improvement on the dielectric properties of ceramic materials and are difficult to meet the demand for dielectric materials for miniaturization of electronic components and energy storage devices. Summary of the Invention

[0005] In light of this, the present invention provides a method for preparing a SrTiO3-based giant dielectric ceramic material simultaneously doped with Lu and Ta. By simultaneously doping Lu and Ta at the A (Sr) and B (Ti) sites of SrTiO3, the resulting SrTiO3-based giant dielectric ceramic material exhibits a giant dielectric effect, low dielectric loss, and excellent frequency and temperature stability of the dielectric constant, meeting the dielectric material requirements for miniaturized electronic components and energy storage devices.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing a Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material comprises the following steps:

[0008] (1) SrCO3, TiO2, Lu2O3 and Ta2O5 are ball-milled once according to the stoichiometric ratio in formula I, and the obtained ball-milled material is dried and then synthesized to obtain a synthetic powder;

[0009] Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 formula I;

[0010] In formula I: 0<x≤0.015;

[0011] (2) ball-milling the synthetic powder for a second time, followed by sieving and drying to obtain a second ball-milled material;

[0012] (3) mixing the secondary ball mill material, a binder and water, and then performing aging, granulation and dry pressing in sequence to obtain a ceramic body;

[0013] (4) Debinding and sintering the ceramic body in sequence to obtain the SrTiO3-based giant dielectric ceramic material doped with Lu and Ta as donors; the sintering atmosphere is nitrogen.

[0014] Preferably, the conditions for the primary ball milling and the secondary ball milling independently include: a ball milling speed of 250 to 350 rpm, a ball milling time of 5 to 7 h, and deionized water as the ball milling medium.

[0015] Preferably, the synthesis temperature is 1150-1250° C., the holding time is 3-5 hours; the heating rate to the synthesis temperature is 4-6° C. / min; and the synthesis atmosphere is air.

[0016] Preferably, the binder is a polyvinyl alcohol solution, and the concentration of the polyvinyl alcohol solution is 3-5 wt.%; the amount of the binder is 1-2% of the mass of the synthetic powder; and the amount of water is 0.5-1% of the mass of the synthetic powder.

[0017] Preferably, the dry pressing pressure is 13-17 MPa; the diameter of the ceramic body is 8-12 mm, and the thickness is 1-2 mm.

[0018] Preferably, the debinding temperature is 550-650° C., and the holding time is 1.5-2.5 h.

[0019] Preferably, the sintering temperature is 1500-1550° C., the holding time is 5-7 hours, and the nitrogen flow rate during the sintering is 60-100 mL / min.

[0020] Preferably, the procedure for heating to the sintering temperature is: first heating to 1200°C at a rate of 4-6°C / min, then heating to 1400°C at a rate of 2-4°C / min, then heating to 1500°C at a rate of 1-3°C / min, and finally heating to the sintering temperature at a rate of 0.5-1.5°C / min.

[0021] The present invention also provides a Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material prepared by the preparation method described in the above scheme, the chemical formula of which is shown in Formula I:

[0022] Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 formula I;

[0023] In formula I: 0<x≤0.015.

[0024] Preferably, the dielectric constant of the SrTiO3-based giant dielectric ceramic material in which Lu and Ta are simultaneously donor-doped is 156,000 to 253,000 at room temperature and a test frequency of 1 kHz, and the dielectric loss is 0.02 to 0.067.

[0025] The present invention provides a method for preparing a SrTiO3-based giant dielectric ceramic material in which Lu and Ta are simultaneously donor-doped, comprising the following steps: (1) ball-milling SrCO3, TiO2, Lu2O3 and Ta2O5 according to the stoichiometric ratio in formula I (see above), drying the obtained first-ball milled material and synthesizing it to obtain a synthetic powder; (2) ball-milling the synthetic powder twice and then sieving and drying it in sequence to obtain a secondary ball milled material; (3) mixing the secondary ball milled material, a binder and water, and then aging, granulating and dry-pressing it in sequence to obtain a ceramic body; (4) debinding and sintering the ceramic body in sequence to obtain the SrTiO3-based giant dielectric ceramic material in which Lu and Ta are simultaneously donor-doped at the A (Sr) position and the B (Ti) position, respectively. The present invention utilizes the strontium vacancies (V″) generated by Lu and Ta being simultaneously donor-doped at the A (Sr) position and the B (Ti) position of SrTiO3. Sr ), oxygen vacancies and Ti 3+ These defect dipoles tend to form stable defect clusters, such as: and These defect clusters increase the local polarizability to achieve the giant dielectric effect, and also limit the long-range displacement of free electrons to achieve the purpose of reducing dielectric loss. In addition, the present invention can obtain a SrTiO3-based giant dielectric ceramic material doped with Lu and Ta by sintering in a nitrogen atmosphere. The ceramic material has a giant dielectric effect, low dielectric loss, and good frequency and temperature stability of the dielectric constant, meeting the needs of miniaturization of electronic components and energy storage devices for dielectric materials. In addition, the amount of dopants Ta2O5 and Lu2O3 used in the present invention is relatively small, which can reduce production costs; the preparation method involved in the present invention is simple, has good repeatability, high yield, low cost, and is convenient for commercial production.

[0026] The results of the embodiment show that when x=0.01, at room temperature and a test frequency of 1 kHz, the dielectric constant of the SrTiO3-based giant dielectric ceramic material doped with Lu and Ta as donors is ∼220,000 and the dielectric loss is ∼0.02. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Sr 0.985 Lu 0.01 Ti 1-x Ta x XRD test results of O3 (x = 0, 0.005, 0.01 and 0.015), where (a) is Sr obtained by sintering at 1525 ° C for 6 h in nitrogen atmosphere. 0.985 Lu 0.01 Ti 1-x Ta xXRD patterns of O3 (x = 0, 0.005, 0.01 and 0.015), (b) is a local magnification of the (222) diffraction peak of Lu2Ti2O7, and (c) is a local magnification of the (110) diffraction peak of SrTiO3;

[0028] Figure 2 Pure SrTiO3 and Sr 0.985 Lu 0.01 Ti 1-x Ta x Backscattered scanning electron micrographs of O3 and Sr 0.985 Lu 0.01 Ti 1-x Ta x The average grain size and relative density test results of O3, where (a) is a backscattered scanning electron microscope photo of pure SrTiO3, (b) to (e) are surface morphology photos of samples with x = 0, 0.005, 0.01 and 0.015 under backscattered scanning electron microscope; (f) is a Sr 0.985 Lu 0.01 Ti 1-x Ta x Variation of the average grain size and relative density of O3 with doping concentration;

[0029] Figure 3 Sr was obtained by sintering at 1525℃ for 6h in nitrogen atmosphere. 0.985 Lu 0.01 Ti 1-x Ta x Dielectric properties of O3 ceramics (x = 0, 0.005, 0.01, and 0.015), where (a) shows the variation of dielectric properties with frequency at room temperature, (b) shows the variation of dielectric properties with doping concentration at room temperature and 1 kHz, and (c) shows the variation of dielectric properties with temperature at 1 kHz. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material, comprising the following steps:

[0031] (1) SrCO3, TiO2, Lu2O3 and Ta2O5 are ball-milled once according to the stoichiometric ratio in formula I, and the obtained ball-milled material is dried and then synthesized to obtain a synthetic powder;

[0032] Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 formula I;

[0033] In formula I: 0<x≤0.015;

[0034] (2) ball-milling the synthetic powder for a second time, followed by sieving and drying to obtain a second ball-milled material;

[0035] (3) mixing the secondary ball mill material, a binder and water, and then performing aging, granulation and dry pressing in sequence to obtain a ceramic body;

[0036] (4) Debinding and sintering the ceramic body in sequence to obtain the SrTiO3-based giant dielectric ceramic material doped with Lu and Ta as donors; the sintering atmosphere is nitrogen.

[0037] The present invention ball-mills SrCO₃, TiO₂, Lu₂O₃, and Ta₂O₅ according to the stoichiometric ratio in Formula I, and the resulting ball-milled material is dried and synthesized to obtain a synthetic powder. In the present invention, the value of x in Formula I is preferably 0.005, 0.01, or 0.015, and more preferably 0.01. In the present invention, the purity of the SrCO3 is preferably above 99%, the purity of the TiO2 is preferably above 99%, the purity of the Lu2O3 is preferably above 99.99%, and the purity of the Ta2O5 is preferably above 99.99%; the conditions for the single ball milling preferably include: a ball milling speed of 250 to 350 rpm, more preferably 280 to 300 rpm, a ball milling time of 5 to 7 hours, more preferably 5.5 to 6.5 hours, and a ball milling medium of deionized water; the ball milling device is preferably a planetary ball mill, and the ball milling jar used for the ball milling is preferably a polytetrafluoroethylene ball milling jar; the present invention has no special requirements for the drying conditions, and drying in an oven is sufficient.

[0038] In the present invention, the synthesis temperature is preferably 1150-1250°C, more preferably 1200°C, the holding time is preferably 3-5 hours, more preferably 4 hours, and the heating rate to the synthesis temperature is preferably 4-6°C / min, more preferably 5°C / min. In a specific embodiment of the present invention, the dried primary milled material is preferably placed in an alumina crucible and then synthesized in a muffle furnace.

[0039] After obtaining the synthetic powder, the present invention performs secondary ball milling on the synthetic powder, followed by screening and drying to obtain a secondary ball milled material. In the present invention, the conditions for the secondary ball milling preferably include: a ball milling speed of 250 to 350 rpm, more preferably 280 to 300 rpm, a ball milling time of 5 to 7 hours, more preferably 5.5 to 6.5 hours, and deionized water as the ball milling medium; the mesh size of the sieve used for screening is preferably 500 mesh; the present invention has no special requirements for the drying conditions, and drying in an oven is sufficient.

[0040] After the secondary ball mill material is obtained, the secondary ball mill material, a binder and water are mixed, and then aging, granulation and dry pressing are sequentially performed to obtain a ceramic body. In the present application, the binder is preferably a polyvinyl alcohol solution, and more preferably an aqueous polyvinyl alcohol solution; the mass concentration of the polyvinyl alcohol solution is preferably 3-5%, and more preferably 4%; the amount of the binder is preferably 1-2% of the mass of the synthetic powder, and more preferably 1.5-2%; the amount of water is preferably 0.5-1% of the mass of the synthetic powder; the water is preferably deionized water; the aging time is preferably 8-24 h, and more preferably 12-20 h; the present application does not have special requirements for the granulation, and the conditions well known in the art can be used; the pressure of the dry pressing is preferably 13-17 MPa, and more preferably 15 MPa; the diameter of the ceramic body is preferably 8-12 mm, and more preferably 10 mm; and the thickness of the ceramic body is preferably 1-2 mm.

[0041] After the ceramic body is obtained, the ceramic body is sequentially subjected to degreasing and sintering to obtain the Lu, Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material; and the sintering is performed in a nitrogen atmosphere. In the present application, the degreasing temperature is preferably 550-650℃, and more preferably 600℃; the degreasing holding time is preferably 1.5-2.5 h, and more preferably 2 h; and the degreasing is preferably performed in a muffle furnace.

[0042] In the present application, the sintering temperature is preferably 1500-1550℃, and more preferably 1525℃; the sintering holding time is preferably 5-7 h, and more preferably 5.5-6.5 h, and further preferably 6 h; the temperature rising procedure to the sintering temperature is preferably as follows: first, the temperature is raised to 1200℃ at a rate of 4-6℃ / min, then the temperature is raised to 1400℃ at a rate of 2-4℃ / min, then the temperature is raised to 1500℃ at a rate of 1-3℃ / min, and finally the temperature is raised to the sintering temperature at a rate of 0.5-1.5℃ / min; and the sintering is preferably performed in a tube furnace.

[0043] The present application also provides a Lu, Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material prepared by the preparation method described in the above scheme, and the chemical formula is shown in formula I:

[0044] Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 formula I;

[0045] In formula I, 0

[0046] In the present application, x in formula I is preferably 0.005, 0.01 or 0.015.

[0047] In the present invention, the dielectric constant of the SrTiO3-based giant dielectric ceramic material simultaneously doped with Lu and Ta as donors is 156,000 to 253,000 at room temperature and a test frequency of 1 kHz, and the dielectric loss is 0.02 to 0.067.

[0048] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] Example 1

[0050] Step 1: Using SrCO3 (purity of 99%), TiO2 (purity of 99%), Ta2O5 (purity of 99.99%) and Lu2O3 (purity of 99.99%) as starting materials, according to the chemical formula Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 (x = 0) weighed the raw materials, the total mass of the raw materials was 30g, the weighed raw materials were added to a polytetrafluoroethylene ball mill, deionized water was used as the ball milling medium, and the mixture was mixed and ball milled on a planetary ball mill at a speed of 300 rpm for 8 hours, and then placed in an oven for drying.

[0051] Step 2: The powder dried in step 1 is placed in an alumina crucible, heated to 1200°C in a muffle furnace at a heating rate of 5°C / min and kept warm for 4 hours to obtain a synthetic powder, and then subjected to secondary ball milling using the same process as step 1, passed through a 500-mesh sieve, and then dried to obtain a secondary ball-milled material.

[0052] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball mill obtained in step 2, and perform aging, granulation, and dry pressing in sequence. The dry pressing pressure is 15 MPa, and the ceramic body obtained by molding has a diameter of 10 mm and a thickness of 2 mm.

[0053] Step 4: Place the ceramic body obtained in step 3 in a muffle furnace and heat it to 600℃ and keep it for 2 hours to remove the binder. Then place it in a tubular furnace and heat it to 1200℃ at a nitrogen flow rate of 80mL / min at a heating rate of 5℃ / min. Then heat it to 1400℃ at 3℃ / min, heat it to 1500℃ at 2℃ / min, and finally heat it to 1525℃ at 1℃ / min and keep it for 6 hours. The sintering process is to obtain Lu and Ta donor-doped SrTiO3-based giant dielectric ceramic materials.

[0054] The sintered ceramic sheet is polished on both sides and coated with silver electrodes, and placed in a muffle furnace to heat to 550°C for 15 min to burn the electrodes. The dielectric property test uses Agilent 4294A impedance analyzer. The test results show that the dielectric constant of the ceramic material is ~ 216000 and the dielectric loss is ~ 0.067 at room temperature and a test frequency of 1 kHz.

[0055] Example 2

[0056] Step 1: SrCO3 (purity 99%), TiO2 (purity 99%), Ta2O5 (purity 99.99%), and Lu2O3 (purity 99.99%) are weighed according to the chemical formula Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 (x = 0.005), and the total mass of the raw materials is 30 g. The weighed raw materials are added to a polytetrafluoroethylene ball mill jar, deionized water is used as the ball milling medium, and the mixture is ball milled on a planetary ball mill at a speed of 300 rpm for 8 h, and then dried in an oven.

[0057] Step 2: The dried powder in step 1 is loaded into an alumina crucible and heated in a muffle furnace at a heating rate of 5°C / min to 1200°C for 4 h to obtain a synthesis powder. The same process as step 1 is used for secondary ball milling, and the secondary ball milling material is dried after being sieved through a 500 mesh sieve.

[0058] Step 3: 0.5 g of a 4 wt% PVA solution and 0.2 g of deionized water are added to the secondary ball milling material obtained in step 2, and aging and granulation are performed in sequence, and dry pressing is performed at a pressure of 15 MPa. The ceramic green body obtained by molding has a diameter of 10 mm and a thickness of 2 mm.

[0059] Step 4: The ceramic green body obtained in step 3 is placed in a muffle furnace and heated to 600°C for 2 h to remove the binder, and then placed in a tube furnace. The nitrogen flow is 80 mL / min, the heating rate is 5°C / min, the temperature is raised to 1200°C, then the temperature is raised to 1400°C at a rate of 3°C / min, the temperature is raised to 1500°C at a rate of 2°C / min, and finally the temperature is raised to 1525°C at a rate of 1°C / min and held for 6 h. The sintering process is used to sinter the Lu, Ta co-doped SrTiO3-based giant dielectric ceramic material.

[0060] The sintered ceramic sheet is polished on both sides and coated with silver electrodes, and placed in a muffle furnace to heat to 550°C for 15 min to burn the electrodes. The dielectric property test uses Agilent 4294A impedance analyzer. The test results show that the dielectric constant of the ceramic material is ~ 156000 and the dielectric loss is ~ 0.029 at room temperature and a test frequency of 1 kHz.

[0061] Example 3

[0062] Step 1: SrCO3 (purity 99%), TiO2 (purity 99%), Ta2O5 (purity 99.99%) and Lu2O3 (purity 99.99%) were used to prepare a 1.5% mol / L 2 O 3 mixture according to the chemical formula Sr 0.985 Lu 0.01 Ti 1-x Ta x O3 (x = 0.01) weighed the raw materials, the total mass of the raw materials was 30 g, the weighed raw materials were added to a polytetrafluoroethylene ball mill, deionized water was used as the ball milling medium, and the mixture was mixed and ball milled on a planetary ball mill at a speed of 300 rpm for 8 h, and then placed in an oven for drying.

[0063] Step 2: The powder dried in step 1 is placed in an alumina crucible, heated to 1200°C in a muffle furnace at a heating rate of 5°C / min and kept warm for 4 hours to obtain a synthetic powder, and then subjected to secondary ball milling using the same process as step 1, passed through a 500-mesh sieve, and then dried to obtain a secondary ball-milled material.

[0064] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball mill obtained in step 2, and perform aging, granulation, and dry pressing in sequence. The dry pressing pressure is 15 MPa, and the ceramic body obtained by molding has a diameter of 10 mm and a thickness of 2 mm.

[0065] Step 4: The ceramic body obtained in step 3 is placed in a muffle furnace and heated to 600°C for 2 hours to remove binder. The body is then placed in a tube furnace and heated at a rate of 5°C / min to 1200°C with a nitrogen flow rate of 80 mL / min. The temperature is then increased at a rate of 3°C / min to 1400°C, then at a rate of 2°C / min to 1500°C, and finally at a rate of 1°C / min to 1525°C and held for 6 hours. This sintering process produces a Lu and Ta co-donor-doped SrTiO3-based giant dielectric ceramic material.

[0066] The sintered ceramic discs were polished on both sides and coated with silver electrodes. The electrodes were then heated to 550°C in a muffle furnace for 15 minutes to sinter the electrodes. Dielectric properties were tested using an Agilent 4294A impedance analyzer. The results showed that the dielectric constant of the ceramic material was ~220,000 and the dielectric loss was ~0.02 at room temperature and a test frequency of 1 kHz.

[0067] Example 4

[0068] Step 1: SrCO3 (purity 99%), TiO2 (purity 99%), Ta2O5 (purity 99.99%) and Lu2O3 (purity 99.99%) were used to prepare a 1.5% mol / L 2 O 3 mixture according to the chemical formula Sr 0.985 Lu 0.01 Ti 1-x Tax O3 (x = 0.015) weighed the raw materials, the total mass of the raw materials was 30 g, the weighed raw materials were added to a polytetrafluoroethylene ball mill, deionized water was used as the ball milling medium, and the mixture was mixed and ball milled on a planetary ball mill at a speed of 300 rpm for 8 h, and then placed in an oven for drying.

[0069] Step 2: The powder dried in step 1 is placed in an alumina crucible, heated to 1200°C in a muffle furnace at a heating rate of 5°C / min and kept warm for 4 hours to synthesize powder, and then ball-milled for the second time using the same process as step 1, passed through a 500-mesh sieve, and dried to obtain a secondary ball-milled material.

[0070] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball mill obtained in step 2, and perform aging, granulation, and dry pressing in sequence. The dry pressing pressure is 15 MPa, and the ceramic body obtained by molding has a diameter of 10 mm and a thickness of 2 mm.

[0071] Step 4: Place the ceramic body obtained in step 3 in a muffle furnace and heat it to 600℃ and keep it for 2 hours to remove the binder. Then place it in a tubular furnace and heat it to 1200℃ at a nitrogen flow rate of 80mL / min at a heating rate of 5℃ / min. Then heat it to 1400℃ at 3℃ / min, heat it to 1500℃ at 2℃ / min, and finally heat it to 1525℃ at 1℃ / min and keep it for 6 hours. The sintering process is to obtain Lu and Ta donor-doped SrTiO3-based giant dielectric ceramic materials.

[0072] The sintered ceramic discs were polished on both sides and coated with silver electrodes. The electrodes were then heated to 550°C in a muffle furnace for 15 minutes to sinter the electrodes. Dielectric properties were tested using an Agilent 4294A impedance analyzer. The results showed that the dielectric constant of the ceramic material was ~253,000 and the dielectric loss was ~0.03 at room temperature and a test frequency of 1 kHz.

[0073] Testing and Characterization

[0074] Testing and characterization of ceramic materials obtained in Examples 1 to 4

[0075] (1) XRD test

[0076] Figure 1 Sr 0.985 Lu 0.01 Ti 1-x Ta x XRD test results of O3 (x = 0, 0.005, 0.01 and 0.015), where (a) is Sr obtained by sintering at 1525 ° C for 6 h in nitrogen atmosphere. 0.985 Lu 0.01 Ti 1-x Ta xXRD patterns of O3 (x = 0, 0.005, 0.01 and 0.015), (b) is a local magnification of the (222) diffraction peak of Lu2Ti2O7, and (c) is a local magnification of the (110) diffraction peak of SrTiO3. Figure 1 As can be seen from (a) in the figure, the main crystalline phase of all samples presents a cubic perovskite structure and corresponds well to PDF#84-0444. A small amount of the second phase Lu2Ti2O7 corresponding to PDF#76-1696 can be detected in all samples with x=0 to 0.015. The local enlarged image of the (222) diffraction peak of Lu2Ti2O7 is shown in the figure. Figure 1 As shown in (b), we can see that as Ta 5+ The (222) diffraction peak intensity of Lu2Ti2O7 gradually increases with the increase of doping concentration, which indicates that Ta 5+ The doping of Ta will compete with Lu for lattice sites at Ti sites, promoting the precipitation of the second phase Lu2Ti2O7. In addition, with the increase of doping concentration, the diffraction peak of Lu2Ti2O7 gradually shifts to a lower angle, which indicates an increase in the unit cell parameters. This may be due to the presence of a small number of Ta with larger ionic radius. 5+ Solid solution into the Lu2Ti2O7 lattice causes lattice expansion. Figure 1 As can be seen in (c), compared with pure SrTiO3, the diffraction peak of the sample with x=0 shifts to a higher angle. This is due to the smaller ionic radius of Lu 3+ Sr dissolved in SrTiO3 2+ The unit cell parameters are reduced. 5+ As the doping amount increases, the diffraction peak gradually shifts to a lower angle, and the unit cell parameter increases to x = 0.015. This is due to the larger ionic radius of Ta 5+ Ti dissolved in SrTiO3 4+ The sites cause an increase in the unit cell parameters.

[0077] (2) Backscattered scanning electron microscopy and average grain size test

[0078] Figure 2 (a) to (e) show pure SrTiO3 and Ta 5+ Backscattered scanning electron microscopy images of the surface morphology of samples with doping concentrations of x = 0, 0.005, 0.01, and 0.015. Bright white particles found at the grain boundaries of samples with x = 0, 0.005, 0.01, and 0.015 are the second phase Lu2Ti2O7. The average grain size was calculated using Nanomeasure software. Figure 2(f) is a graph showing the variation of average grain size with doping concentration. Compared with pure SrTiO3, the average grain size of the x=0 sample increases sharply from 2.09μm to 19.59μm, which is mainly due to the Lu 3+ However, as Ta 5+ As the doping level increases, the grain size gradually decreases to 5.91 μm at x = 0.015. This reduction in grain size is related to the pinning effect of the second phase. Ta doping facilitates the precipitation of the second phase, enhancing its pinning effect. Therefore, despite increasing defect concentration, the average grain size remains around 6 μm as the second phase Lu2Ti2O7 content increases. Figure 2 (f) in the figure also shows the change of relative density with doping concentration. It can be found that the relative density of the ceramic material is the largest at x=0, which is 97.32%, and then decreases slightly, which may be related to the change of its grain size.

[0079] (3) Dielectric performance test

[0080] Figure 3 The SrO2 obtained by sintering at 1525℃ for 6h in nitrogen atmosphere is shown. 0.985 Lu 0.01 Ti 1-x Ta x Dielectric properties of O3 ceramics (x = 0, 0.005, 0.01 and 0.015). Figure 3 (a) shows the change of dielectric properties with frequency at room temperature. All Sr sintered in N2 0.985 Lu 0.01 Ti 1-x Ta x The O3 ceramics all exhibit similar dielectric responses, with a slight decrease in dielectric constant at higher frequencies, which may be related to the interface polarization, as the interface polarization does not respond at high frequencies. Figure 3 (b) shows the change of dielectric properties with doping concentration at room temperature and 1kHz. It can be found that compared with pure SrTiO3, single element doping of Lu (x = 0) will make the dielectric constant (ε r ) increases to ~216000, and the dielectric loss (tanδ) increases to ~0.067. As the Ta doping amount gradually increases, the dielectric constant and dielectric loss show a trend of first decreasing and then increasing. The best dielectric performance is obtained when x=0.01, and the dielectric constant is ε r ~220000, and the dielectric loss is tanδ~0.02. Combined with the above XPS defect analysis, it can be seen that the improvement of dielectric performance is closely related to the defect concentration. Figure 3 (c) shows the change of dielectric properties with temperature at 1kHz. It can be found that Ta 5+The temperature stability of the dielectric loss of the doped samples has been significantly improved, which may be related to the increase in defect concentration.

[0081] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a SrTiO3-based giant dielectric ceramic material doped with Lu and Ta as donors, characterized in that: The following steps are involved: (1) SrCO3, TiO2, Lu2O3 and Ta2O5 are ball-milled once according to the stoichiometric ratio in formula I, and the obtained ball-milled material is dried and then synthesized to obtain a synthetic powder; Sr 0.985 Lu 0.01 Ti 1-x The x O3 formula I; In formula I: 0<x≤0.015; (2) ball-milling the synthetic powder for a second time, followed by sieving and drying to obtain a second ball-milled material; (3) mixing the secondary ball mill material, a binder and water, and then performing aging, granulation and dry pressing in sequence to obtain a ceramic body; (4) Debinding and sintering the ceramic body in sequence to obtain the SrTiO3-based giant dielectric ceramic material doped with Lu and Ta as donors; the sintering atmosphere is nitrogen.

2. The preparation method according to claim 1, characterized in that The conditions for the primary ball milling and the secondary ball milling independently include: a ball milling speed of 250 to 350 rpm, a ball milling time of 5 to 7 hours, and deionized water as the ball milling medium.

3. The preparation method according to claim 1, characterized in that The synthesis temperature is 1150-1250° C., and the holding time is 3-5 hours. The heating rate to the synthesis temperature is 4-6° C. / min. The synthesis atmosphere is air.

4. The preparation method according to claim 1, characterized in that The binder is a polyvinyl alcohol solution with a concentration of 3-5 wt.%. The amount of the binder is 1-2% of the mass of the synthetic powder. The amount of water is 0.5-1% of the mass of the synthetic powder.

5. The preparation method according to claim 1, characterized in that The dry pressing pressure is 13-17 MPa; the diameter of the ceramic body is 8-12 mm, and the thickness is 1-2 mm.

6. The preparation method according to claim 1, characterized in that The debinding temperature is 550-650° C., and the heat preservation time is 1.5-2.5 hours.

7. The preparation method according to claim 1, characterized in that The sintering temperature is 1500-1550° C., the holding time is 5-7 hours, and the nitrogen flow rate during the sintering is 60-100 mL / min.

8. The preparation method according to claim 1 or 7, characterized in that The procedure for heating to the sintering temperature is: first heating to 1200°C at a rate of 4-6°C / min, then heating to 1400°C at a rate of 2-4°C / min, then heating to 1500°C at a rate of 1-3°C / min, and finally heating to the sintering temperature at a rate of 0.5-1.5°C / min.

9. The Lu and Ta donor-doped SrTiO3-based giant dielectric ceramic material prepared by the preparation method according to any one of claims 1 to 7 has a chemical formula as shown in Formula I: Sr 0.985 Lu 0.01 Ti 1-x The x O3 formula I; In formula I: 0<x≤0.

015.

10. The Lu and Ta simultaneously donor-doped SrTiO3-based giant dielectric ceramic material according to claim 9, characterized in that: The Lu and Ta donor-doped SrTiO3-based giant dielectric ceramic material has a dielectric constant of 156,000 to 253,000 and a dielectric loss of 0.02 to 0.03 at room temperature and a test frequency of 1 kHz.

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