A Ta, Al co-doped strontium titanate-based giant dielectric ceramic material and its preparation method

Abstract

The present invention relates to the technical field of electronic functional materials, and provides a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material and a preparation method thereof. In the present invention, SrTiO3 is co-doped with Ta and Al, and the dielectric constant of the obtained Ta, Al co-doped SrTiO3-based giant dielectric ceramic material is on the order of 10 5 magnitude, and the frequency and temperature stability of the dielectric constant are good, which can meet the requirements of miniaturization of electronic components and dielectric materials for energy storage devices. Moreover, when preparing the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material in the present invention, it is not necessary to use a hydrogen atmosphere, and it can be sintered only under nitrogen conditions, with good safety, low cost, and easy for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic functional materials, and particularly relates to a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material and a preparation method thereof. Background Art

[0002] Giant dielectric ceramics have great application prospects in energy storage and miniaturization of electronic components. Common giant dielectric ceramic materials include BaTiO3, CaCu3Ti4O 12 , NiO, and TiO2, etc. Among them, since BaTiO3 is a ferroelectric material, a ferroelectric phase transition occurs at the Curie temperature of 120 °C, resulting in a sharp increase in its dielectric constant to 6000-10000, which affects its use at high temperatures; doping CaCu3Ti4O 12 -based ceramics can obtain a giant dielectric effect and the dielectric constant can be maintained stable within a wide temperature and frequency range, but the relatively high dielectric loss limits its application; NiO-based ceramics also have the problem that it is difficult to reduce the dielectric loss (>0.3); although the doped TiO2-based ceramics have both a giant dielectric constant and a low dielectric loss, their breakdown strength is relatively low, making it difficult to apply. Therefore, it is very important to develop a ceramic material with a giant dielectric constant, low dielectric loss, high breakdown strength, and good temperature and frequency stability of dielectric properties.

[0003] Pure SrTiO3 has a relatively low Curie temperature (102 K) and can maintain a paraelectric phase at room temperature. Therefore, its dielectric constant can be maintained stable within a relatively wide temperature range. In addition, it also has the advantages of high breakdown strength and low dielectric loss. However, the intrinsic dielectric constant of pure-phase SrTiO3 ceramics is relatively low (~300), which is difficult to meet the application of giant dielectric materials. Therefore, it is necessary to improve its dielectric properties by means of doping modification and improving the sintering process. Pu et al. successfully prepared single-element doped strontium titanate ceramics sintered in an inert atmosphere or a reducing atmosphere, such as: Sr 1-1.5x Re x TiO3 (Re = La, Dy, Nd, Y, Ce, and Er) ceramics, and the results show that these ceramics have a giant dielectric effect (>10 4 ). However, many results also show that single-element doping modification is not flexible enough to obtain comprehensive and diverse excellent dielectric properties. Co-doping can provide greater freedom to manipulate its structure and dielectric properties, such as SrTi prepared by Pan (Giant dielectric response in (Nb+Zn) co-doped strontium titanate ceramics tailored by atmosphere, Scr. Mater. 170 (2019) 166-171.) et al. 0.985 (Zn1 / 3 Nb 2 / 3 ) 0.015 The Nb, O3 ceramics sintered in a nitrogen atmosphere can obtain a giant dielectric constant of ~51000 and a low dielectric loss of ~0.03; the Nb, Mg co-doped SrTiO3 ceramics sintered in an air atmosphere prepared by Zhong et al. (Colossal dielectric permittivity in co-doping SrTiO3 ceramics by Nb and Mg, Ceram. Int. 46 (2020) 20565-20569.) can obtain a dielectric constant of 21026 and a dielectric loss of 0.0354; the Nb, Li co-doped SrTiO3 ceramics prepared by Chen et al. (Colossal permittivity and low dielectric loss in (Li, Nb) co-doped SrTiO3 ceramics with high frequency and temperature stability, Ceram. Int. 48 (2022) 36393-36400.) can increase the dielectric constant to ~17300, and the dielectric loss is controlled at ~0.017. However, the dielectric constants of most SrTiO3-based giant dielectric ceramics are less than 10 5 orders of magnitude. Currently, only the Er-doped SrTiO3 ceramics prepared by Pu et al. (Simultaneously achieving colossal permittivity, ultralow dielectric loss tangent, and high insulation resistivity in Er-doped SrTiO3 ceramics via oxygen vacancy regulation. ACS Applied Materials & Interfaces, 43 (2022) 48821-48832.) have obtained a dielectric constant of ~130000. However, this ceramic material needs to be sintered in a hydrogen atmosphere, and due to the inflammability and explosiveness of hydrogen, its large-scale production is limited.

[0004] In summary, the dielectric constants of current SrTiO3-based ceramic materials need to be improved, and the sintering atmosphere is harsh. There is an urgent need to develop an SrTiO3-based ceramic material with a dielectric constant in the order of 10 5 orders of magnitude that does not need to be sintered under hydrogen and is easy to produce on a large scale. Summary of the Invention

[0005] In view of this, the present invention provides a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material and a preparation method thereof. The Ta, Al co-doped SrTiO3-based giant dielectric ceramic material provided by the present invention has a dielectric constant in the order of 10 5 magnitude, and has good frequency and temperature stability of the dielectric constant. Moreover, the giant dielectric ceramic material does not require a hydrogen atmosphere during sintering and can be sintered only under nitrogen conditions, making it easy to carry out large-scale production.

[0006] To achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0007] A Ta, Al co-doped SrTiO3-based giant dielectric ceramic material, the chemical formula of which is shown in Formula I:

[0008] SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 Formula I;

[0009] In Formula I: the value range of x is 2% < x ≤ 5%.

[0010] Preferably, the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material has a dielectric constant of 123,000 to 225,000 at room temperature and a test frequency of 1 kHz, and the dielectric loss range is 0.04 to 0.07.

[0011] The present invention also provides a preparation method of the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material described in the above solution, including the following steps:

[0012] (1) According to the stoichiometric ratio in Formula I, SrCO3, TiO2, Al2O3 and Ta2O5 are ball-milled for the first time. After drying the obtained first-time ball-milled material, it is calcined to obtain a calcined powder;

[0013] (2) The calcined powder is ball-milled for the second time and then sieved and dried in sequence to obtain a second-time ball-milled material;

[0014] (3) The second-time ball-milled material, a binder and water are mixed and then aged, granulated and dry-pressed into a ceramic green body in sequence;

[0015] (4) The ceramic green body is degummed and sintered in sequence to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material; the sintering is carried out in a nitrogen atmosphere.

[0016] Preferably, the conditions of the first-time ball milling and the second-time ball milling independently include: the ball milling speed is 250 to 350 rpm, the ball milling time is 5 to 7 h, and the ball milling medium is deionized water.

[0017] Preferably, the temperature of the calcination is 1150 - 1250 °C, the heat preservation time is 3 - 5 h; the heating rate to the calcination temperature is 4 - 6 °C / min; the atmosphere of the calcination is air.

[0018] Preferably, the binder is a polyvinyl alcohol solution, and the mass concentration of the polyvinyl alcohol solution is 3 - 5%; the dosage of the binder is 1 - 2% of the mass of the calcined powder; the dosage of the water is 0.5 - 1% of the mass of the calcined powder.

[0019] Preferably, the pressure of the dry pressing is 13 - 17 MPa; the diameter of the ceramic green body is 8 - 12 mm, and the thickness is 1 - 2 mm.

[0020] Preferably, the temperature of the debinding is 550 - 650 °C, and the heat preservation time is 1.5 - 2.5 h.

[0021] Preferably, the temperature of the sintering is greater than 1500 °C and less than or equal to 1550 °C, the heat preservation time is 5 - 7 h, and the gas flow rate of the nitrogen is 60 - 100 mL / min.

[0022] Preferably, the procedure for heating to the sintering temperature is: first, heat at a rate of 4 - 6 °C / min to 1200 °C, then heat at a rate of 2 - 4 °C / min to 1400 °C, then heat at a rate of 1 - 3 °C / min to 1500 °C, and finally heat at a rate of 0.5 - 1.5 °C / min to the sintering temperature.

[0023] The present invention provides a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material, and the chemical formula is as shown in Formula I (see above). The present invention utilizes the oxygen vacancies and free electrons (e′) generated by Ta, Al co-doping SrTiO3. Ti 4+ inside the ceramic obtains an electron and is reduced to Ti 3+ . These defect dipoles tend to form stable defect clusters (for example: ). The existence of the defect clusters will pin the freely moving electrons, thereby enhancing the polarizability to achieve the giant dielectric effect. The Ta, Al co-doped SrTiO3-based giant dielectric ceramic material provided by the present invention has a dielectric constant in the order of 10 5 , and the frequency and temperature stability of the dielectric constant are good, which can meet the requirements of miniaturization of electronic components and dielectric materials for energy storage devices.

[0024] The present invention also provides a method for preparing the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material described in the above solution. First, SrCO3, TiO2, Ta2O5, and Al2O3 are ball-milled once according to the stoichiometric ratio in Formula I. After drying the obtained primary ball-milled material, it is calcined to obtain a calcined powder. The calcined powder is ball-milled twice and then sieved and dried in sequence to obtain a secondary ball-milled material. The secondary ball-milled material, binder, and water are mixed and then subjected to aging, granulation, and dry pressing in sequence to obtain a ceramic green body. The ceramic green body is subjected to debinding and sintering in sequence to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material. The sintering is carried out in a nitrogen atmosphere. When preparing the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material, the present invention does not need to use a hydrogen atmosphere and only needs to be sintered under nitrogen conditions, with good safety. Moreover, in the present invention, the dosages of the dopants Ta2O5 and Al2O3 are small, which can further reduce the production cost. Additionally, the preparation method provided by the present invention has simple steps, good repeatability, high yield, low cost, and is convenient for commercial production.

[0025] The results of the examples show that when x = 4%, at room temperature and a test frequency of 1 kHz, the dielectric constant of the obtained Ta, Al co-doped SrTiO3-based giant dielectric ceramic material is ~125,000, the dielectric loss is ~0.05, and the frequency and temperature stabilities of the dielectric properties are good. Description of the Drawings

[0026] Figure 1 XRD pattern of the SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) ceramic material sintered at 1525 °C for 6 h in a nitrogen atmosphere;

[0027] Figure 2 Surface morphology diagrams of the SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) ceramic material sintered at 1525 °C for 6 h in a nitrogen atmosphere, where: (a) x = 0%, (b) x = 0.5%, (c) x = 1%, (d) x = 2%, (e) x = 3%, (f) x = 4%, and (g) x = 5%;

[0028] Figure 3 XRD pattern of the SrTi 1-x (Ta 0.5 Al 0.5 ) xDielectric properties of O3 (0% < x ≤ 5%) ceramic materials, where: (a) shows the variation of dielectric properties with frequency at room temperature, (b) shows the variation of dielectric properties with doping amount at room temperature and 1 kHz, and (c) shows the variation of dielectric properties with temperature at 1 kHz. Detailed implementation mode

[0029] The present invention provides a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material, which is characterized in that the chemical formula is as shown in Formula I:

[0030] SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 Formula I;

[0031] In Formula I: the value range of x is 2% < x ≤ 5%.

[0032] In the present invention, the value of x is preferably 3%, 4%, or 5%, and more preferably 4%. By using Ta, Al co-doped SrTiO3 in the present invention, a certain number of stable defect clusters are formed inside the ceramic, increasing the polarizability, so that the obtained ceramic material has a giant dielectric effect.

[0033] In the present invention, the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material preferably has a dielectric constant of 123,000 to 225,000 and a dielectric loss range of 0.04 to 0.07 at a test frequency of 1 kHz at room temperature.

[0034] The present invention also provides a preparation method of the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material described in the above scheme, including the following steps:

[0035] (1) According to the stoichiometric ratio in Formula I, SrCO3, TiO2, Ta2O5 and Al2O3 are ball-milled once, and the obtained primary ball-milled material is dried and then calcined to obtain a calcined powder;

[0036] (2) The calcined powder is ball-milled twice and then sieved and dried in sequence to obtain a secondary ball-milled material;

[0037] (3) The secondary ball-milled material, binder and water are mixed and then aged, granulated and dry-pressed into a ceramic green body in sequence;

[0038] (4) The ceramic green body is degummed and sintered in sequence to obtain a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material; the sintering is carried out in a nitrogen atmosphere.

[0039] In the present invention, SrCO3, TiO2, Ta2O5 and Al2O3 are ball-milled once according to the stoichiometric ratio in Formula I, and the obtained primary ball-milled material is dried and then calcined to obtain a calcined powder. 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 Al2O3 is preferably above 99%, and the purity of the Ta2O5 is preferably above 99.99%. In the present invention, the conditions for the primary ball milling preferably include: the ball milling speed is 250-350 rpm, more preferably 280-320 rpm, the ball milling time is 5-7 h, more preferably 6 h, and the ball milling medium is deionized water; the device for the primary ball milling is preferably a planetary ball mill, and the ball milling tank used for the primary ball milling is preferably a polytetrafluoroethylene ball milling tank. The present invention has no special requirements for the drying conditions, and it can be dried in an oven.

[0040] In the present invention, the calcination temperature is preferably 1150-1250 °C, more preferably 1200 °C, the holding time for the calcination is preferably 3-5 h, more preferably 4 h; the heating rate for heating to the calcination temperature is preferably 4-6 °C / min, more preferably 5 °C / min. In a specific embodiment of the present invention, it is preferred to place the dried primary ball-milled material in an alumina crucible and then perform calcination in a muffle furnace.

[0041] After obtaining the calcined powder, the present invention performs secondary ball milling on the calcined powder and then performs sieving and drying in sequence to obtain a secondary ball-milled material. In the present invention, the conditions for the secondary ball milling preferably include: the ball milling speed is 250-350 rpm, more preferably 280-320 rpm, the ball milling time is 5-7 h, more preferably 6 h, and the ball milling medium is deionized water; the mesh number of the sieve used for sieving is preferably 500 mesh; the present invention has no special requirements for the drying conditions, and it can be dried in an oven.

[0042] After obtaining the secondary ball-milled material, the present invention mixes the secondary ball-milled material, a binder and water, and then performs aging, granulation and dry pressing molding in sequence to obtain a ceramic green body. In the present invention, the binder is preferably a polyvinyl alcohol solution, and the mass concentration of the polyvinyl alcohol solution is preferably 3-5%, more preferably 4%; the dosage of the binder is preferably 1-2% of the mass of the calcined powder, and the dosage of the water is preferably 0.5-1% of the mass of the calcined powder; the water is preferably deionized water. In the present invention, the aging time is preferably 8-24 h, more preferably 10-12 h; the aging temperature is preferably room temperature. The present invention has no special requirements for the granulation, and the conditions well-known in the art can be adopted. In the present invention, the pressure for the dry pressing molding is preferably 13-17 MPa, more preferably 15 MPa; the diameter of the ceramic green body is preferably 8-12 mm, more preferably 10 mm, and the thickness is preferably 1-2 mm.

[0043] After obtaining the ceramic green body, the present invention sequentially dewaxes and sinters the ceramic green body to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material; the sintering is carried out in a nitrogen atmosphere. In the present invention, the temperature of the dewaxing is preferably 550-650 °C, more preferably 600 °C, the heat preservation time of the dewaxing is preferably 1.5-2.5 h, more preferably 2 h; the dewaxing is preferably carried out in a muffle furnace.

[0044] In the present invention, the temperature of the sintering (denoted as T) is preferably greater than 1500 °C and less than or equal to 1550 °C (i.e., 1500 °C < T ≤ 1550 °C), more preferably 1510-1550 °C, most preferably 1525 °C, the heat preservation time of the sintering is preferably 5-7 h, more preferably 5.5-6.5 h, and further preferably 6 h.

[0045] In the present invention, the procedure for heating up to the sintering temperature is as follows: first, heat up to 1200 °C at a rate of 4-6 °C / min, then heat up to 1400 °C at a rate of 2-4 °C / min, then heat up to 1500 °C at a rate of 1-3 °C / min, and finally heat up to the sintering temperature at a rate of 0.5-1.5 °C / min.

[0046] In the present invention, the sintering is preferably carried out in a tube furnace. In the present invention, the sintering is carried out in a nitrogen atmosphere, and the flow rate of the nitrogen is preferably 80 mL / min.

[0047] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0048] The purity of SrCO3 used in the following examples is 99%, the purity of TiO2 is 99%, the purity of Ta2O5 is 99.99%, and the purity of Al2O3 is 99%.

[0049] Example 1

[0050] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) xFor O3 (x = 3%), the total mass of the raw materials weighed is 30 g. The weighed raw materials are added to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mixed and ball milled at a speed of 300 rpm on a planetary ball mill for 8 h, and then placed in an oven to dry, obtaining the primary ball milled material.

[0051] Step 2: Load the primary ball milled material in Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C and hold for 4 h to obtain the calcined powder, and perform secondary ball milling, sieving through a 500-mesh sieve and drying using the same process as in Step 1 to obtain the 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 milled material obtained in Step 2, age for 12 h, then granulate and dry press into shape. The dry pressing pressure is 15 MPa. The diameter of the formed ceramic green body is 10 mm and the thickness is 2 mm. Place the ceramic green body in a muffle furnace, heat it to 600 °C and hold for 2 h to remove the binder.

[0053] Step 4: Place the binder-removed ceramic green body obtained in Step 3 in a tubular furnace, with a nitrogen flow rate of 80 mL / min, heat it to 1200 °C at a heating rate of 5 °C / min, then heat it to 1400 °C at a heating rate of 3 °C / min, then heat it to 1500 °C at a heating rate of 2 °C / min, and finally heat it to 1525 °C at a heating rate of 1 °C / min and hold for 6 h for the sintering process to sinter the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0054] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes, place it in a muffle furnace, heat it to 550 °C and hold for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. At room temperature and a test frequency of 1 kHz, the dielectric constant of the ceramic material is ~123000 and the dielectric loss is ~0.04.

[0055] Example 2

[0056] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as the starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 4%), the total mass of the raw materials weighed is 30 g. The weighed raw materials are added to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mixed and ball milled at a speed of 300 rpm on a planetary ball mill for 8 h, and then placed in an oven to dry, obtaining the primary ball milled material.

[0057] Step 2: Load the primary ball-milled material from Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C, hold for 4 h to obtain a calcined powder, and then perform secondary ball milling, screen through a 500-mesh sieve, and dry it using the same process as in Step 1 to obtain a secondary ball-milled material.

[0058] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball-milled material obtained in Step 2, let it age for 12 h, then granulate and dry-press it into shape. The dry-pressing pressure is 15 MPa, and the formed ceramic green body has a diameter of 10 mm and a thickness of 2 mm. Place the ceramic green body in a muffle furnace, heat it to 600 °C, and hold for 2 h to remove the binder.

[0059] Step 4: Place the binder-removed ceramic green body obtained in Step 3 in a tube furnace, with a nitrogen flow rate of 80 mL / min, heat it at a rate of 5 °C / min to 1200 °C, then heat it at a rate of 3 °C / min to 1400 °C, then heat it at a rate of 2 °C / min to 1500 °C, and finally heat it at a rate of 1 °C / min to 1525 °C and hold for 6 h according to the sintering process to obtain a Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0060] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes, then place it in a muffle furnace, heat it to 550 °C, and hold for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material at room temperature and a test frequency of 1 kHz is ~125000, and the dielectric loss is ~0.05.

[0061] Example 3

[0062] Step 1: Using SrCO3, TiO2, Ta2O5, and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 5%), weigh a total of 30 g of raw materials, add the weighed raw materials with deionized water as the ball-milling medium into a polytetrafluoroethylene ball-milling tank, and mix and ball-mill at a speed of 300 rpm on a planetary ball mill for 8 h, then put it into an oven to dry, to obtain a primary ball-milled material.

[0063] Step 2: Load the primary ball-milled material from Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C, hold for 4 h to obtain a calcined powder, and then perform secondary ball milling, screen through a 500-mesh sieve, and dry it using the same process as in Step 1 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-milled abrasive obtained in Step 2. After aging for 12 h, granulation and dry pressing are carried out. The dry pressing pressure is 15 MPa. The formed ceramic green body has a diameter of 10 mm and a thickness of 2 mm. The ceramic green body is placed in a muffle furnace and heated to 600 °C for 2 h to remove the binder.

[0065] Step 4: Place the binder-removed ceramic green body obtained in Step 3 in a tube furnace. With a nitrogen flow rate of 80 mL / min, heat it to 1200 °C at a heating rate of 5 °C / min, then heat it to 1400 °C at a rate of 3 °C / min, then heat it to 1500 °C at a rate of 2 °C / min, and finally heat it to 1525 °C at a rate of 1 °C / min and hold for 6 h for the sintering process to obtain Ta, Al co-doped SrTiO3-based giant dielectric ceramic materials.

[0066] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes. Place it in a muffle furnace and heat it to 550 °C for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material is ~225000 and the dielectric loss is ~0.07 at room temperature and a test frequency of 1 kHz.

[0067] Example 4

[0068] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 4%), weigh the total mass of the raw materials as 30 g. Add the weighed raw materials to a polytetrafluoroethylene ball mill tank with deionized water as the ball milling medium, and mix and ball mill at a speed of 300 rpm on a planetary ball mill for 8 h, then put it into an oven to dry to obtain the primary ball-milled abrasive.

[0069] Step 2: Load the primary ball-milled abrasive in Step 1 into an alumina crucible, heat it to 1200 °C at a heating rate of 5 °C / min in a muffle furnace and hold for 4 h to obtain the calcined powder, and use the same process as in Step 1 for secondary ball milling, passing through a 500-mesh sieve and then drying to obtain the secondary ball-milled abrasive.

[0070] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball-milled abrasive obtained in Step 2, age, granulate, and dry press. The dry pressing pressure is 15 MPa. The formed ceramic green body has a diameter of 10 mm and a thickness of 2 mm. The ceramic green body is placed in a muffle furnace and heated to 600 °C for 2 h to remove the binder.

[0071] Step 4: Place the debinded ceramic green body obtained in Step 3 in a tube furnace, and sinter it at a nitrogen flow rate of 80 mL / min with a heating rate of 5 °C / min to 1200 °C, then heat it to 1400 °C at a rate of 3 °C / min, then to 1500 °C at a rate of 2 °C / min, and finally to 1550 °C at a rate of 1 °C / min and hold for 6 h to obtain Ta, Al co-doped SrTiO3-based giant dielectric ceramic materials.

[0072] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes, then place it in a muffle furnace and heat it to 550 °C and hold for 15 min to burn the electrodes. The dielectric properties were tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material at room temperature and a test frequency of 1 kHz is ~173000, and the dielectric loss is ~0.17.

[0073] Comparative Example 1

[0074] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 0.5%), weigh a total of 30 g of the raw materials, add the weighed raw materials with deionized water as the ball milling medium to a polytetrafluoroethylene ball milling tank, and mix and ball mill at a speed of 300 rpm on a planetary ball mill for 8 h, then put it into an oven to dry to obtain the primary ball milled material.

[0075] Step 2: Load the primary ball milled material in Step 1 into an alumina crucible, heat it to 1200 °C at a heating rate of 5 °C / min in a muffle furnace and hold for 4 h to obtain the calcined powder, and perform secondary ball milling using the same process as in Step 1, sieve it through a 500-mesh sieve and then dry it to obtain the secondary ball milled material.

[0076] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball milled material obtained in Step 2, age for 12 h, then granulate and dry press it. The dry pressing pressure is 15 MPa, and the formed ceramic green body has a diameter of 10 mm and a thickness of 2 mm. Place the ceramic green body in a muffle furnace and heat it to 600 °C and hold for 2 h to remove the binder.

[0077] Step 4: Place the debinded ceramic green body in Step 3 in a tube furnace, and sinter it at a nitrogen flow rate of 80 mL / min with a heating rate of 5 °C / min to 1200 °C, then heat it to 1400 °C at a rate of 3 °C / min, then to 1500 °C at a rate of 2 °C / min, and finally to 1525 °C at a rate of 1 °C / min and hold for 6 h to obtain Ta, Al co-doped SrTiO3-based giant dielectric ceramic materials.

[0078] The ceramic chips obtained by sintering were polished on both sides and coated with silver electrodes, and then placed in a muffle furnace, heated to 550 °C and kept warm for 15 min to burn the electrodes. The dielectric properties were tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material was ~5400 and the dielectric loss was ~0.25 at room temperature and a test frequency of 1 kHz.

[0079] Comparative Example 2

[0080] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 1%), the total mass of the raw materials was weighed as 30 g. The weighed raw materials were added to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mixed and ball milled on a planetary ball mill at a speed of 300 rpm for 8 h, and then put into an oven to dry, obtaining the primary ball milled material.

[0081] Step 2: The primary ball milled material in Step 1 was loaded into an alumina crucible, heated in a muffle furnace at a heating rate of 5 °C / min to 1200 °C and kept warm for 4 h to obtain the calcined powder, and then subjected to secondary ball milling using the same process as in Step 1, passed through a 500-mesh sieve and dried to obtain the secondary ball milled material.

[0082] Step 3: 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water were added to the secondary ball milled material obtained in Step 2. After aging for 12 h, granulation and dry pressing were carried out. The dry pressing pressure was 15 MPa. The diameter of the formed ceramic green body was 10 mm and the thickness was 2 mm. The ceramic green body was placed in a muffle furnace, heated to 600 °C and kept warm for 2 h to remove the binder.

[0083] Step 4: The ceramic green body after binder removal obtained in Step 3 was placed in a tube furnace. With a nitrogen flow rate of 80 mL / min, it was heated to 1200 °C at a heating rate of 5 °C / min, then heated to 1400 °C at a heating rate of 3 °C / min, then heated to 1500 °C at a heating rate of 2 °C / min, and finally heated to 1525 °C at a heating rate of 1 °C / min and kept warm for 6 h for the sintering process to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0084] The ceramic chips obtained by sintering were polished on both sides and coated with silver electrodes, and then placed in a muffle furnace, heated to 550 °C and kept warm for 15 min to burn the electrodes. The dielectric properties were tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material was ~15000 and the dielectric loss was ~0.31 at room temperature and a test frequency of 1 kHz.

[0085] Comparative Example 3

[0086] Step 1: Using SrCO3, TiO2, Ta2O5, and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 2%), weigh the total mass of the raw materials as 30 g. Add the weighed raw materials to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mix and ball mill on a planetary ball mill at a rotation speed of 300 rpm for 8 h, then put it into an oven to dry, obtaining the primary ball milled material.

[0087] Step 2: Load the primary ball milled material from Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C and hold for 4 h to obtain the calcined powder. Then use the same process as in Step 1 for secondary ball milling, pass through a 500-mesh sieve, and dry to obtain the secondary ball milled material.

[0088] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball milled material obtained in Step 2. After aging for 12 h, carry out granulation and dry pressing. The dry pressing pressure is 15 MPa. The formed ceramic green body has a diameter of 10 mm and a thickness of 2 mm. Place the ceramic green body in a muffle furnace, heat it to 600 °C and hold for 2 h to remove the binder.

[0089] Step 4: Place the binder-removed ceramic green body obtained in Step 3 in a tube furnace, with a nitrogen flow rate of 80 mL / min, heat it at a heating rate of 5 °C / min to 1200 °C, then heat it at 3 °C / min to 1400 °C, then heat it at 2 °C / min to 1500 °C, and finally heat it at 1 °C / min to 1525 °C and hold for 6 h for the sintering process to sinter and obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0090] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes, then place it in a muffle furnace, heat it to 550 °C and hold for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. At room temperature and a test frequency of 1 kHz, the dielectric constant of the ceramic material is ~77000, and the dielectric loss is ~0.09.

[0091] Comparative Example 4

[0092] Step 1: Using SrCO3, TiO2, Ta2O5, and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) xFor O3 (x = 4%), the total mass of the raw materials weighed is 30 g. The weighed raw materials are added to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mixed and ball milled on a planetary ball mill at a rotational speed of 300 rpm for 8 h, and then placed in an oven to dry, obtaining the primary ball milled material.

[0093] Step 2: Load the primary ball milled material in Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C and hold for 4 h to obtain the calcined powder, and perform secondary ball milling using the same process as in Step 1, sieve through a 500-mesh sieve and then dry to obtain the secondary ball milled material.

[0094] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary ball milled material obtained in Step 2, age for 12 h, then granulate and dry press into shape. The dry pressing pressure is 15 MPa. The diameter of the formed ceramic green body is 10 mm and the thickness is 2 mm. Place the ceramic green body in a muffle furnace, heat it to 600 °C and hold for 2 h to remove the binder.

[0095] Step 4: Place the binder-removed ceramic green body obtained in Step 3 in a tubular furnace, with a nitrogen flow rate of 80 mL / min, heat it at a heating rate of 5 °C / min to 1200 °C, then heat it at 3 °C / min to 1400 °C, and then heat it at 2 °C / min to 1500 °C and hold for 6 h for the sintering process to sinter the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0096] Polish both sides of the sintered ceramic sheet and coat it with silver electrodes, place it in a muffle furnace, heat it to 550 °C and hold for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. The dielectric constant of the ceramic material at room temperature and a test frequency of 1 kHz is ~63000, and the dielectric loss is ~0.17.

[0097] Comparative Example 5

[0098] Step 1: Using SrCO3, TiO2, Ta2O5 and Al2O3 as starting materials, according to the chemical formula SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (x = 4%), the total mass of the raw materials weighed is 30 g. The weighed raw materials are added to a polytetrafluoroethylene ball milling tank with deionized water as the ball milling medium, and mixed and ball milled on a planetary ball mill at a rotational speed of 300 rpm for 8 h, and then placed in an oven to dry, obtaining the primary ball milled material.

[0099] Step 2: Load the primary milled abrasive in Step 1 into an alumina crucible, heat it in a muffle furnace at a heating rate of 5 °C / min to 1200 °C, keep it for 4 h to calcine the powder, and perform secondary ball milling using the same process as in Step 1. After passing through a 500-mesh sieve, dry it to obtain the secondary milled abrasive.

[0100] Step 3: Add 0.5 g of 4 wt% PVA solution and 0.2 g of deionized water to the secondary milled abrasive obtained in Step 2, age and granulate it, and then perform dry pressing. The dry pressing pressure is 15 MPa. The diameter of the formed ceramic green body is 10 mm and the thickness is 2 mm. Place the ceramic green body in a muffle furnace, heat it to 600 °C, and keep it for 2 h to remove the binder.

[0101] Step 4: Place the debound ceramic green body obtained in Step 3 in a tube furnace. The sintering atmosphere is air. The sintering process is to heat it to 1200 °C at a heating rate of 5 °C / min, then heat it to 1400 °C at a heating rate of 3 °C / min, then heat it to 1500 °C at a heating rate of 2 °C / min, and finally heat it to 1525 °C at a heating rate of 1 °C / min and keep it for 6 h to sinter the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material.

[0102] Polish both sides of the sintered ceramic piece and coat it with silver electrodes. Place it in a muffle furnace, heat it to 550 °C, and keep it for 15 min to burn the electrodes. The dielectric properties are tested using an Agilent 4294A impedance analyzer. At room temperature and a test frequency of 1 kHz, the dielectric constant of the ceramic material is ~2700, and the dielectric loss is ~0.02.

[0103] Performance test:

[0104] 1. Summarize the dielectric property test data of the ceramic materials obtained in Examples 1-4 and Comparative Examples 1-5 in Table 1 as follows:

[0105] Table 1 Dielectric properties of samples prepared in Examples 1-4 and Comparative Examples 1-5

[0106]

[0107] It can be seen from the data in Table 1 that the ceramic materials sintered in a nitrogen atmosphere in Examples 1-4 of the present invention all have a giant dielectric constant. When x = 4% and the sintering temperature is 1525 °C, the dielectric constant of the obtained ceramic material at room temperature and a test frequency of 1 Hz reaches ~125000, and the dielectric loss is ~0.05, and the frequency stability of the dielectric properties is good. While in Comparative Examples 1, 2, and 3, the doping concentration was changed, in Comparative Example 4, the sintering temperature of the ceramic green body was changed, and in Comparative Example 5, the sintering atmosphere of the ceramic green body was changed. The dielectric properties of the obtained ceramic materials are poor and cannot meet the requirements of giant dielectric ceramic materials.

[0108] 2. Testing and characterization of ceramic materials

[0109] Figure 1 SrTi sintered at 1525°C for 6 h in a nitrogen atmosphere 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) XRD pattern of the ceramic material. The results show that the SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) ceramic materials are all in the pure SrTiO3 phase and no secondary phase is formed, indicating that Ta and Al can all enter the SrTiO3 lattice.

[0110] Figure 2 SrTi sintered at 1525°C for 6 h in a nitrogen atmosphere 1-x (Ta 0.5 Al 0.5 ) x Surface morphology of O3 (0% < x ≤ 5%) ceramic materials, where: (a) x = 0%, (b) x = 0.5%, (c) x = 1%, (d) x = 2%, (e) x = 3%, (f) x = 4%, and (g) x = 5%; Figure 2 The results in show that as the doping amount increases from 0% to 2%, the grain size gradually increases. This is mainly due to the presence of oxygen vacancies, which enhances the mass transfer in the grains, promotes the movement of grain boundaries, and leads to an increase in grain size. However, when the doping amount increases from 2% to 5%, the grain size gradually decreases. This is because a higher doping concentration inhibits the formation of defects such as oxygen vacancies, resulting in a decrease in the grain boundary mobility and inhibiting grain growth.

[0111] Figure 3 SrTi sintered at 1525°C for 6 h in a nitrogen atmosphere 1-x (Ta 0.5 Al 0.5 ) x Dielectric properties of O3 (0% < x ≤ 5%) ceramic materials, where (a) is the variation of dielectric properties with frequency at room temperature, (b) is the variation of dielectric properties with doping amount at room temperature and 1 kHz, and (c) is the variation of dielectric properties with temperature at 1 kHz. Figure 3 The results in (a) show that the SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) ceramic materials prepared by the present invention have good frequency stability of dielectric constant and dielectric loss. Figure 3The result in (b) shows that when x = 4%, the highest dielectric constant (~125000) and relatively low dielectric loss (~0.05) can be obtained. Figure 3 The result in (c) indicates that the SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 (0% < x ≤ 5%) ceramic material has good temperature stability of dielectric constant and dielectric loss.

[0112] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A Ta, Al co-doped SrTiO3-based giant dielectric ceramic material, characterized in that, The chemical formula is as shown in Formula I: SrTi 1-x (Ta 0.5 Al 0.5 ) x O3 type I; In Formula I: the value range of x is 2% < x ≤ 5%; The preparation method of the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material includes the following steps: (1) According to the stoichiometric ratio in Formula I, SrCO3, TiO2, Al2O3 and Ta2O5 are ball-milled for the first time. After drying the obtained first-time ball-milled material, it is calcined to obtain a calcined powder; (2) The obtained calcined powder is ball-milled for the second time and then sieved and dried in sequence to obtain a second-time ball-milled material; (3) The second-time ball-milled material, binder and water are mixed and then aged, granulated and dry-pressed into a ceramic green body in sequence; (4) The ceramic green body is degummed and sintered in sequence to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material; the sintering is carried out in a nitrogen atmosphere; the sintering temperature is greater than 1500 °C and less than or equal to 1550 °C.

2. The Ta, Al co-doped SrTiO3-based giant dielectric ceramic material according to claim 1, characterized in that, The Ta, Al co-doped SrTiO3-based giant dielectric ceramic material has a dielectric constant of 123,000 - 225,000 and a dielectric loss range of 0.04 - 0.07 at room temperature and a test frequency of 1 kHz.

3. The preparation method of the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material according to claim 1 or 2, characterized in that, It includes the following steps: (1) According to the stoichiometric ratio in Formula I, SrCO3, TiO2, Al2O3 and Ta2O5 are ball-milled for the first time. After drying the obtained first-time ball-milled material, it is calcined to obtain a calcined powder; (2) The obtained calcined powder is ball-milled for the second time and then sieved and dried in sequence to obtain a second-time ball-milled material; (3) The second-time ball-milled material, binder and water are mixed and then aged, granulated and dry-pressed into a ceramic green body in sequence; (4) The ceramic green body is degummed and sintered in sequence to obtain the Ta, Al co-doped SrTiO3-based giant dielectric ceramic material; the sintering is carried out in a nitrogen atmosphere; the sintering temperature is greater than 1500 °C and less than or equal to 1550 °C.

4. The preparation method according to claim 3, characterized in that, The conditions of the first-time ball-milling and the second-time ball-milling independently include: the ball-milling speed is 250 - 350 rpm, the ball-milling time is 5 - 7 h, and the ball-milling medium is deionized water.

5. The preparation method according to claim 3, characterized in that, The calcination temperature is 1150 - 1250 °C, the heat preservation time is 3 - 5 h; the heating rate to the calcination temperature is 4 - 6 °C / min; the calcination atmosphere is air.

6. The preparation method according to claim 3, wherein The binder is a polyvinyl alcohol solution, and the mass concentration of the polyvinyl alcohol solution is 3 - 5%; the dosage of the binder is 1 - 2% of the mass of the calcined powder; the dosage of water is 0.5 - 1% of the mass of the calcined powder.

7. The preparation method according to claim 3, characterized in that The pressure of the dry pressing is 13 - 17 MPa; the diameter of the ceramic green body is 8 - 12 mm, and the thickness is 1 - 2 mm.

8. The preparation method according to claim 3, characterized in that, The degumming temperature is 550 - 650 °C, and the heat preservation time is 1.5 - 2.5 h.

9. The preparation method according to claim 3, wherein The heat preservation time of the sintering is 5 - 7 h, and the gas flow rate of the nitrogen is 60 - 100 mL / min.

10. The preparation method according to claim 9, characterized in that, The procedure for heating up to the sintering temperature is as follows: First, heat up at a rate of 4 - 6 °C / min to 1200 °C, then heat up at a rate of 2 - 4 °C / min to 1400 °C, then heat up at a rate of 1 - 3 °C / min to 1500 °C, and finally heat up at a rate of 0.5 - 1.5 °C / min to the sintering temperature.

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