Preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramic

Abstract

The invention discloses a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramic, belongs to the technical field of ceramic preparation, solves the problem that the dielectric constant and dielectric loss of CCTO are simultaneously increased or reduced when CCTO is subjected to single-doping modification in the prior art, and comprises the following steps: carrying out primary ball milling treatment on a powder raw material, and drying after ball milling treatment is finished, so that the Sr / Co co-doped CCTO giant dielectric ceramic is obtained. Pre-sintering the precursor powder, carrying out secondary ball milling treatment on the pre-sintered powder, drying the pre-sintered powder subjected to secondary ball milling treatment to obtain ceramic powder, carrying out tabletting molding on the ceramic powder, and sintering a green body to obtain the Sr / Co co-doped CCTO giant dielectric ceramic material. According to the invention, Sr < 2 + > ions are used for carrying out substitution doping on Ca < 2 + > ion sites, so that the grain boundary resistance and the Schottky barrier height can be effectively increased, the dielectric relaxation characteristic can be enhanced, Co < 2 + > ions are used for carrying out substitution doping on Cu < 2 + > ion sites, and CaTiO3 and Co2TiO4 phases can be formed at the grain boundary, so that the grain boundary resistivity and the dielectric loss are reduced, and the dielectric relaxation performance is improved. The effect of effectively regulating and controlling the dielectric property of the ceramic is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic preparation, and particularly relates to a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramics. Background Art

[0002] With the continuous development of electronic science and technology, people's demand for energy is increasing continuously. The energy problem has attracted wide attention. We urgently need renewable energy to cope with the increasing energy consumption. At the same time, developing efficient and low-cost energy storage devices is also a key problem to be solved. Currently, the commonly used storage devices mainly include capacitors, batteries and generators. Among them, dielectric capacitors, as an electrochemical energy storage device, have broad research prospects. Among them, giant dielectric materials in dielectric materials have broad application prospects in the microelectronics field and play an important role in the miniaturization and high speed of devices. However, it is still a difficult challenge to obtain giant dielectric materials with high dielectric constant, low dielectric loss and good temperature stability at the same time.

[0003] Currently, among the common giant dielectric materials, BaTiO3-based ceramics, belonging to ferroelectric materials, have two obvious disadvantages: one is that ferroelectric-paraelectric phase transition occurs at the Curie temperature, which makes the dielectric constant change significantly with temperature and the stability is poor; the other is that many ferroelectric dielectric materials contain lead, which is harmful to the human body. SrTiO3-based ceramics have a perovskite-like crystal structure and a wide bandgap (~3.2 eV), and are an excellent dielectric material with moderate dielectric constant and low loss, but usually cannot meet the requirements of a wider temperature range. TiO2-based ceramics have a rutile structure, and the dielectric loss increases rapidly with the increase of frequency, and the grain size is relatively large, making it difficult to achieve miniaturization. After modification, they have a relatively large dielectric constant and good dielectric thermal stability.

[0004] Since Subramanian et al. reported that CCTO material has a high dielectric constant, CCTO, as a mainstream giant dielectric ceramic material, has been attracting the attention of many researchers. It is a chalcogenide with a body-centered cubic structure, and the lattice constant is Ti atoms are located at the center of the oxygen octahedron, and the 8 vertices of the octahedron are respectively occupied by Ca 2+ and Cu 2+Occupying in a ratio of 1:3, the resulting TiO6 octahedra are connected to six adjacent different CuO4, making the TiO6 octahedral structure tilted. This special structure of CCTO is the main reason why it can have excellent dielectric constant, temperature stability, frequency stability and non-linear electrical properties, which enables it to be used as a high-energy density storage medium. Although CCTO has many advantages, there are still some disadvantages that limit its use, such as high dielectric loss. Modern electronic device applications urgently need to reduce the dielectric loss while increasing the dielectric constant. Therefore, how to maintain a high dielectric constant and reduce the dielectric loss of CCTO materials is an urgent problem to be solved.

[0005] Current researchers have improved the performance of CCTO in various ways, such as: single doping, co-doping, multiple composites, shell structures, etc. Among them, doping is a very effective modification method. Chun-Hong Mu (C.-H. Mu, P. Liu, Y. He, J.-P. Zhou, H.-W. Zhang, An effective method to decrease dielectric loss ofCaCu3Ti4O 12 ceramics, J. Alloys Compd. 471(2009)137e141.) et al. doped Sr into CCTO ceramics 2+ , and their results showed that the change in the grain boundary structure led to a decrease in dielectric loss, but the dielectric constant decreased to 10 4 or less. Z. Kaf et al. (Z. Kafi, A. Kompany, H. Arabi, A. Khorsand Zak, The effect of cobalt-doping onmicrostructure and dielectric properties of CaCu3Ti4O 12 ceramics, J. Alloy. Compd. 727(2017)168-176.) believed that the dielectric loss (tanδ) could be reduced by controlling the structure and chemical properties of the grain boundary region in CCTO ceramics. By reducing the CuO phase with semiconductor behavior, and by Co 2+ at the Cu 2+Instead, CaTiO3 and Co2TiO4 phases with good dielectric insulation properties are formed in the grain boundaries to reduce the leakage current caused by the grain boundary conductivity, thereby reducing the dielectric loss and the increase in dielectric constant in CCTO ceramics. Compared with single doping, where there are defects such as simultaneous increase or decrease of dielectric constant and dielectric loss, co-doping is an effective method to improve its performance. However, there is less research on co-doping. To address the above problems, we propose a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramics. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramics in view of the deficiencies of the prior art, and to solve the problem that when the prior art modifies CCTO by single doping, the dielectric constant and dielectric loss of CCTO increase or decrease simultaneously.

[0007] When the prior art modifies CCTO by single doping, there is a problem that the dielectric constant and dielectric loss of CCTO increase or decrease simultaneously. To address the above problems, we propose a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramics. In the present invention, using Sr 2+ ions to replace and dope the Ca 2+ ion sites can effectively increase the grain boundary resistance and the height of the Schottky barrier, and can enhance the dielectric relaxation characteristics. By Co 2+ ions to replace and dope the Cu 2+ ion sites will form CaTiO3 and Co2TiO4 phases at the grain boundaries, realizing the reduction of the Cu-rich phase, thereby reducing the grain boundary resistivity and dielectric loss, and achieving the effect of effectively regulating the dielectric properties of the ceramics.

[0008] The present invention is implemented as follows. A preparation method of Sr / Co co-doped CCTO giant dielectric ceramics, the preparation method of Sr / Co co-doped CCTO giant dielectric ceramics includes:

[0009] S10. Take the powder raw materials for preparing co-doped CCTO giant dielectric ceramics. The powder raw materials include CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder. After proportioning the CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder according to the stoichiometric ratio, add alcohol, and perform a primary ball milling treatment on the powder raw materials. After the ball milling treatment is completed, dry to obtain the precursor powder.

[0010] S20. Take the precursor powder, perform pre-sintering on the precursor powder to obtain the pre-sintered powder, and set it aside.

[0011] S30. Obtain the pre-sintered powder, perform secondary ball milling on the pre-sintered powder, and dry the pre-sintered powder after secondary ball milling to obtain ceramic powder for standby.

[0012] S40. Take the ceramic powder, perform tablet pressing on the ceramic powder to obtain a green body for standby.

[0013] S50. Take the green body and sinter the green body to obtain the Sr / Co co-doped CCTO giant dielectric ceramic material.

[0014] Preferably, in step S10, the particle size of the powder raw material is less than 250 nm. When performing primary ball milling on the powder raw material, zirconia balls are used as grinding balls, absolute ethanol is used as the ball milling medium, the mass ratio of the powder raw material to zirconia balls is 1:2.5 - 3, the mass ratio of absolute ethanol to the powder raw material is 1:1.1 - 1.3, the primary ball milling speed is 450 - 500 r / min, and the primary ball milling time is 12 - 24 h.

[0015] Preferably, in step S20, when pre-sintering the precursor powder, the pre-sintering temperature is 900 - 1000 °C, the heating rate from room temperature to the pre-sintering temperature is 3 - 5 °C / min, and the pre-sintering time is 8 - 10 h.

[0016] Preferably, in step S30, the speed of the secondary ball milling is 450 - 550 r / min, and the time of the secondary ball milling is 12 - 20 h.

[0017] Preferably, in step S40, when performing tablet pressing on the ceramic powder, the tablet pressing method adopts the first forming method or the second forming method.

[0018] Preferably, the first forming method includes:

[0019] Take the ceramic powder, and sequentially perform pre-pressing forming and cold isostatic pressing on the ceramic powder. The temperature of the cold isostatic pressing is room temperature, the pressure of the cold isostatic pressing is 200 - 250 MPa, and the time of the cold isostatic pressing is 2 - 5 min.

[0020] Preferably, the second forming method includes:

[0021] Take the ceramic powder, mix the ceramic powder with a binder and granulate to obtain powder particles;

[0022] Press the obtained powder particles into a shape or sequentially perform pre-pressing forming and cold isostatic pressing on the obtained powder particles;

[0023] When adopting the second forming method, degumming the obtained green body is also included before sintering. The temperature of the degumming is 500 - 550 °C, and the heat preservation time is 6 - 9 h.

[0024] Preferably, in step S50, the green body sintering temperature is 1050 - 1100 °C, and the heat preservation time for sintering is 8 - 10 h.

[0025] Preferably, the chemical composition of the Sr / Co co-doped CCTO giant dielectric ceramic material is Ca 1-x Sr x Cu 3- y Co y Ti4O 12 .

[0026] The present invention also provides an application of the preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic in a dielectric capacitor.

[0027] Compared with the prior art, the embodiments of the present application mainly have the following beneficial effects:

[0028] In the present invention, substituting and doping the Ca 2+ ion sites with Sr 2+ ions can effectively increase the grain boundary resistance and the Schottky barrier height, and can enhance the dielectric relaxation characteristics. By substituting and doping the Cu 2+ ion sites with Co 2+ ions, CaTiO3 and Co2TiO4 phases will be formed at the grain boundary, realizing the reduction of the Cu-rich phase, thereby reducing the grain boundary resistivity and dielectric loss, and achieving the effect of effectively regulating the dielectric properties of the ceramic. The dielectric constant of the CSCCTO giant dielectric ceramic material provided by the present invention can reach 10 4 or more, and the dielectric loss can be as low as 0.04. Description of the Drawings

[0029] Figure 1 Shows the SEM micrographs of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1 - 4 of the present invention.

[0030] Figure 2 Shows the XRD diffraction patterns of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1 - 4 of the present invention.

[0031] Figure 3 Shows the curves of the relative dielectric constant and dielectric loss of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1 - 4 of the present invention varying with frequency.

[0032] Figure 4 Shows the variation diagram of the dielectric constant of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1 - 4 of the present invention with temperature at a specific frequency.

[0033] Figure 5 The figure shows the variation of the dielectric loss of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1-4 of the present invention with temperature at a specific frequency. Detailed implementation manners

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification and claims of this application or the above drawings are used to distinguish different objects and not to describe a specific order.

[0035] When the prior art performs single doping modification on CCTO, there is a problem that the dielectric constant and dielectric loss of CCTO increase or decrease simultaneously. In view of the above problems, we propose a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramics. In the present invention, by using Sr 2+ ions to replace and dope the Ca 2+ ion sites, the grain boundary resistance and the Schottky barrier height can be effectively increased, and the dielectric relaxation characteristics can be enhanced. By using Co 2+ ions to replace and dope the Cu 2+ ion sites, CaTiO3 and Co2TiO4 phases will be formed at the grain boundaries, realizing the reduction of the Cu-rich phase, thereby reducing the grain boundary resistivity and dielectric loss, and achieving the effect of effectively regulating the dielectric properties of the ceramics.

[0036] The embodiments of the present invention provide a preparation method of Sr / Co co-doped CCTO giant dielectric ceramics. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramics specifically includes:

[0037] S10, taking the powder raw materials for preparing the co-doped CCTO giant dielectric ceramics. The powder raw materials include CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder. After proportioning the CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder according to the stoichiometric ratio, adding alcohol, and performing primary ball milling on the powder raw materials, and drying after the ball milling is completed to obtain the precursor powder;

[0038] It should be noted that in step S10, the particle size of the powder raw material is less than 250 nm. The present invention has no special requirements for the sources of the various powders, and commercially available products well-known to those skilled in the art can be used. When performing primary ball milling on the powder raw material, zirconia balls are used as the grinding balls, and anhydrous ethanol is used as the ball milling medium. The mass ratio of the powder raw material to the zirconia balls is 1:2.5 - 3, and the mass ratio of anhydrous ethanol to the powder raw material is 1:1.1 - 1.3. The rotation speed of the primary ball milling is 450 - 500 r / min, more preferably 550 r / min, and the primary ball milling time is 12 - 24 h, more preferably 15 - 20 h. In the present invention, the primary ball milling is preferably carried out in a planetary ball mill, and the planetary ball mill preferably uses a nylon ball milling tank. The present invention has no special limitation on the model of the planetary ball mill, and instruments and equipment well-known to those skilled in the art can be used.

[0039] Meanwhile, the present invention mixes the various components in the powder raw material evenly through primary ball milling. After the primary ball milling, it is also preferred to separate the grinding balls from the obtained ball milled material, and then perform drying, grinding, and sieving in sequence to obtain a uniform precursor powder. The present invention has no special limitation on the operation of the manual grinding, and operations well-known to those skilled in the art can be used. The present invention preferably pours the ball milled material after separating the grinding balls into an evaporating dish, and then places the evaporating dish in a drying oven for drying. The drying temperature is preferably 80 - 90 °C, and the time is preferably 12 - 24 h; the sieving is preferably through an 80-mesh sieve, and the material under the sieve is taken to obtain the precursor powder.

[0040] S20: Take the precursor powder, perform pre-sintering on the precursor powder to obtain a pre-sintered powder for standby;

[0041] It should be noted that in step S20, when performing pre-sintering on the precursor powder, the pre-sintering temperature is 900 - 1000 °C, the heating rate from room temperature to the pre-sintering temperature is 3 - 5 °C / min, and the pre-sintering time is 8 - 10 h.

[0042] After obtaining the precursor powder, the present invention performs pre-sintering on the precursor powder to obtain a pre-sintered powder. The present invention preferably places the precursor powder in an alumina crucible, covers the alumina crucible, and then performs pre-sintering. The pre-sintering temperature is preferably 950 - 1000 °C; the heating rate from room temperature to the pre-sintering temperature is preferably 3 - 4 °C / min; the holding time of the pre-sintering is more preferably 8 - 10 h. Through the pre-sintering, the present invention enables the various oxide components to initially undergo chemical reactions, reducing the shrinkage rate of the product during sintering. The control of the pre-sintering temperature has a great influence on controlling the shrinkage rate, the activity of the powder, and determining the final sintering temperature. After the pre-sintering is completed, the present invention preferably naturally cools the obtained pre-sintered product to room temperature and then grinds it to obtain the pre-sintered powder.

[0043] S30. Obtain the pre-sintered powder, perform secondary ball milling on the pre-sintered powder, and dry the pre-sintered powder after the secondary ball milling to obtain ceramic powder for standby.

[0044] In step S30, the rotation speed of the secondary ball milling is 450 - 550 r / min, and the time of the secondary ball milling is 12 - 20 h.

[0045] It should be noted that after obtaining the pre-sintered powder, the present invention performs secondary ball milling on the pre-sintered powder, shapes the obtained ceramic powder to obtain a green body sample. In the present invention, the ball mill, grinding balls, ball milling medium and their dosages used in the secondary ball milling are preferably the same as those in the primary ball milling, which will not be elaborated here; the rotation speed of the secondary ball milling is preferably 500 r / min, and the time of the secondary ball milling is preferably 12 - 13 h. The pre-sintered powder will agglomerate. The present invention grinds the ceramic powder into powder with a certain particle size (particle diameter 0.5 - 0.8 μm) through the secondary ball milling, so that the particle size distribution of the powder is relatively narrow, which is beneficial to shaping. In the present invention, the time of the secondary ball milling has a great influence on the material properties. If the ball milling time is too short, the particle size of the powder is too large. If the ball milling time is too long, it not only has little influence on the particle size of the powder, but also brings in impurities, thereby reducing the material properties. After the secondary ball milling, the present invention preferably dries, grinds and sieves the obtained milled material in sequence to obtain ceramic powder. The present invention preferably pours the milled material into an evaporating dish, places the evaporating dish in a drying oven for drying, the temperature of the drying is preferably 80°C, and the time is preferably 24 h; the sieving is preferably through a 100-mesh sieve, and the material passing through the sieve is taken.

[0046] S40. Take the ceramic powder, perform tablet pressing on the ceramic powder to obtain a green body for standby.

[0047] In the embodiment of the present invention, in step S40, when performing tablet pressing on the ceramic powder, the tablet pressing method adopts the first forming method or the second forming method.

[0048] Among them, the first forming method includes:

[0049] Take the ceramic powder, perform pre-pressing and cold isostatic pressing on the ceramic powder in sequence. The temperature of the cold isostatic pressing is room temperature, the pressure of the cold isostatic pressing is 200 - 250 MPa, and the time of the cold isostatic pressing is 2 - 5 min.

[0050] Specifically, the first forming method preferably includes: subjecting the ceramic powder to pre-pressing (denoted as the first pre-pressing, also known as tablet pressing) and cold isostatic pressing (denoted as the first cold isostatic pressing) in sequence to obtain a green body. In the present invention, the pressure of the first pre-pressing is preferably 100 - 180 MPa, more preferably 100 - 150 MPa, and the pressure holding time is preferably 1 min; in the present invention, it is preferred to place the ceramic powder in a stainless-steel mold and place it in a manual tableting machine, and perform the first pre-pressing under the above pressure conditions. In the embodiments of the present invention, specifically, the ceramic powder is placed in a cylindrical stainless-steel mold, and the ceramic powder is pressed into a cylindrical sample. The pressure of the first cold isostatic pressing is preferably 200 - 250 MPa, more preferably 230 - 250 MPa, and the pressure holding time is preferably 2 min.

[0051] And the second forming method includes:

[0052] Taking ceramic powder, mixing the ceramic powder with a binder and granulating to obtain powder particles;

[0053] Pressing the obtained powder particles into shape or subjecting the obtained powder particles to pre-pressing and cold isostatic pressing in sequence;

[0054] The second forming method preferably includes: mixing the ceramic powder with a binder and granulating, and pressing the obtained powder particles into shape to obtain a green body. In the present invention, the binder is preferably a polyvinyl alcohol (PVA) solution, and the mass fraction of the polyvinyl alcohol solution is preferably 5 - 10%; the mass ratio of the ceramic powder to the polyvinyl alcohol solution is preferably 5:1. The present invention has no special requirements for the specific operation method of the granulation, and the granulation methods well-known to those skilled in the art can be used. In the present invention, the pressure of the pressing into shape is preferably 200 - 230 MPa, and the pressure holding time is preferably 1 min; in the present invention, it is preferred to pass the powder particles obtained after granulation through 60-mesh and 100-mesh sieves, and then take the uniform particles on the 100-mesh sieve for pressing into shape. Alternatively, the second forming method preferably includes: subjecting the above-obtained powder particles to pre-pressing (denoted as the second pre-pressing) and cold isostatic pressing (denoted as the second cold isostatic pressing) in sequence to obtain a green body. In the present invention, the pressure of the second pre-pressing is preferably 100 - 180 MPa, more preferably 160 - 180 MPa, and the pressure holding time is preferably 1 min; the pressure of the second cold isostatic pressing is preferably 200 - 250 MPa, more preferably 200 - 220 MPa, and the pressure holding time is preferably 2 min.

[0055] When the second forming method is adopted, degumming the obtained green body is further included before sintering, and the temperature of the degumming is 500 - 550 °C, and the heat preservation time is 6 - 9 h.

[0056] In the present invention, when the forming adopts the second forming method, it is also preferably to degrease the obtained green body before sintering. In the present invention, the temperature of the degreasing is preferably 500 - 550 °C, more preferably 500 - 520 °C, the heat preservation time is preferably 6 - 9 h, more preferably 8 - 9 h; through the degreasing of the present invention, the binder in the green body is fully decomposed, volatilized or removed, so as to prevent the green body from deforming or cracking during the sintering process, thereby being beneficial to obtaining high-quality ceramic sintered samples.

[0057] S50, Take the green body and sinter the green body to obtain the Sr / Co co-doped CCTO giant dielectric ceramic material.

[0058] Among them, the chemical formula of CCTO is CaCu3Ti4O 12 . In this embodiment, in step S50, the sintering temperature of the green body is 1050 - 1100 °C, and the heat preservation time of the sintering is 8 - 10 h.

[0059] After obtaining the green body, the present invention sinters the green body to obtain the CSCCTO giant dielectric ceramic material. In the present invention, the heating rate for rising to the sintering temperature is preferably 3 - 5 °C / min; the heat preservation time of the sintering is more preferably 9 - 10 h; the sintering is preferably carried out in an air atmosphere. In the present invention, the sintering is a process of solid-phase reaction. In the present invention, both the degreasing and the sintering are preferably carried out in a muffle furnace; after the sintering, it is preferably cooled naturally to room temperature.

[0060] It should be noted that the chemical composition of the Sr / Co co-doped CCTO giant dielectric ceramic material prepared in the embodiment of the present invention is Ca 1-x Sr x Cu 3-y Co y Ti4O 12 (x is 0 - 0.1, y is 0 - 0.1).

[0061] In the present invention, using Sr 2+ ions to substitute and dope the Ca 2+ ion sites can effectively increase the grain boundary resistance and the Schottky barrier height, and can enhance the dielectric relaxation characteristics. By using Co 2+ ions to substitute and dope the Cu 2+ ion sites, CaTiO3 and Co2TiO4 phases will be formed at the grain boundary, realizing the reduction of the Cu-rich phase, thereby reducing the grain boundary resistivity and the dielectric loss, achieving the effect of effectively regulating the dielectric properties of the ceramic. The dielectric constant of the CSCCTO giant dielectric ceramic material provided by the present invention can reach 10 4 or more, and the dielectric loss can be as low as 0.04.

[0062] Example 1

[0063] In this embodiment, a preparation method of Sr / Co co-doped CCTO giant dielectric ceramics is provided. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramics specifically includes:

[0064] S101, weighing and mixing: Weigh CaCO3 powder, CuO powder, and TiO2 powder (the particle size of the above powders is less than 250 nm) as raw materials for batching by stoichiometry; load the mixed powder and zirconia balls into a ball mill tank according to a mass ratio of 1:2.5, and add a certain mass of absolute ethanol (the mass ratio of absolute ethanol to the mixed powder is 1:1.2), and perform wet ball milling for 18 h in a planetary ball mill at a rotation speed of 550 r / min; after drying, grinding, and sieving (passing through an 80-mesh sieve and taking the undersize), a uniform precursor powder is obtained.

[0065] S102, pre-sintering and grinding: Load the precursor powder into a zirconia crucible, keep it at 1000 °C (heating rate is 3 °C / min) for 10 h in a high-temperature muffle furnace, open the furnace after natural cooling to room temperature, and obtain the pre-sintered powder after grinding again.

[0066] S103, forming: After subjecting the pre-sintered powder to secondary ball milling (adding zirconia balls and absolute ethanol, rotation speed is 500 r / min, ball milling time is 12 h), drying, and grinding, add a 5 wt.% polyvinyl alcohol (PVA) solution (the mass ratio of the powder to the PVA solution is 5:1) as a binder to the ground powder for granulation, and after passing through 60-mesh and 100-mesh sieves, take the uniform powder particles on the 100-mesh sieve and put them into a stainless-steel mold with a diameter of 10 mm for pre-pressing to make a disc-shaped sample, and then put it into a cold isostatic press and keep it under a pressure of 200 MPa for 2 min to prepare a cylindrical green body sample.

[0067] S104, debinding and sintering: Load the cylindrical green body sample into a zirconia crucible and put it into a high-temperature muffle furnace, keep it at 500 °C for 9 h for debinding, and then sinter it in an air atmosphere at 1090 °C for 8 h, and obtain the sample after cooling to room temperature with the furnace.

[0068] Example 2

[0069] In the embodiment of the present invention, the raw materials in step S101 of Example 1 are changed to CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and the remaining steps of the preparation method of the Sr / Co co-doped CCTO giant dielectric ceramics are the same as those in Example 1.

[0070] Example 3

[0071] In the embodiment of the present invention, the raw materials in step S101 of Embodiment 1 are changed to CaCO3 powder, CuO powder, TiO2 powder, CoO powder, and the remaining steps of the preparation method of Sr / Co co-doped CCTO giant dielectric ceramics are the same as those in Embodiment 1.

[0072] Embodiment 4

[0073] In the embodiment of the present invention, the raw materials in step S101 of Embodiment 1 are changed to CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, CoO powder, and the remaining steps of the preparation method of Sr / Co co-doped CCTO giant dielectric ceramics are the same as those in Embodiment 1.

[0074] Performance test:

[0075] Take the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Embodiments 1-4 of the present invention and conduct SEM micro-morphology, XRD diffraction pattern, and electrical property tests respectively. Among them, the SEM micro-morphology is tested by a scanning electron microscope, and the XRD diffraction pattern is tested by an X-ray diffractometer. The test results are as Figure 1 and Figure 2 shown.

[0076] Among them, Figure 1 shows the SEM micro-morphology diagrams of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Embodiments 1-4 of the present invention. Figure 1 In Figure 1 , (a)-(d) respectively correspond to the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Embodiments 1-4. It can be seen that the grains of the Sr / Co co-doped CCTO giant dielectric ceramic sample prepared in Embodiment 4 are smaller than those of other embodiments, indicating that Sr / Co co-doping reduces the grain size of CCTO, the number of grain boundaries increases significantly, the electrostatic potential barrier increases, the dielectric loss decreases, and the microstructure is relatively dense, and there are no obvious micropores and other defects on the surface.

[0077] Figure 2 shows the XRD diffraction patterns of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Embodiments 1-4 of the present invention. It can be seen from Figure 2 that all samples show a perovskite-like structure similar to that of CaCu3Ti4O 12 ceramics (CCTO), indicating that the CSCCTO ceramic samples have been successfully prepared.

[0078] The Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1-4 of the present invention were polished, and silver electrodes were made (the thickness and diameter of the ceramic material samples needed to be measured), and then electrical property tests were carried out. When making silver electrodes, silver paste was coated or printed on the upper and lower surfaces of the ceramic material samples, and then placed in a muffle furnace and baked at 600 °C for 30 min. The test results are as Figures 3 - 5 shown in Table 1.

[0079] Among them, Figure 3 shows the curves of the relative dielectric constant (ε') and dielectric loss (tanδ) of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1-4 of the present invention varying with frequency. Figure 3 In (a), it is the curve of the dielectric constant of the sample varying with frequency, and in (b), it is the curve of the dielectric loss of the sample varying with frequency. From Figure 3 it can be seen that all the Sr / Co co-doped CCTO giant dielectric ceramic samples in the examples exhibited giant dielectric constant response (above 10 4 ), and had good stability throughout the frequency test range. In addition, the dielectric loss of the Sr / Co co-doped CCTO giant dielectric ceramic samples basically showed a trend of first decreasing and then increasing with the increase of the test frequency. At high frequencies, the significant relaxation peak in the dielectric loss spectrum was closely related to the change of the dielectric constant observed in the graph of the relationship between the dielectric constant and frequency. And in the range of 10 2 -10 3 Hz, the dielectric loss of the Sr / Co co-doped CCTO giant dielectric ceramic sample in Example 4 was relatively low. This phenomenon indicates that Sr / Co co-doped CCTO giant dielectric ceramics can effectively reduce the dielectric loss at low frequencies.

[0080] Figure 4 shows the graph of the dielectric constant of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1-4 of the present invention varying with temperature at a specific frequency. From Figure 4 it can be seen that all the Sr / Co co-doped CCTO giant dielectric ceramic samples in the examples exhibited huge dielectric constants (above 10 4 ) in the temperature range of 30 °C - 210 °C, and at the same time showed excellent stability in the temperature range of 30 °C - 210 °C. The dielectric constant of all ceramics increased with the increase of the test temperature, which was related to the synergistic effect of electrode polarization and carrier migration. And it can be observed that the dielectric constant of all samples showed a downward trend with the increase of frequency, indicating that in this temperature range, thermally activated processes such as interfacial polarization began to work. The dielectric constant was relatively stable at lower temperatures, and at higher temperatures, the low-frequency variation amplitude increased significantly and remained stable at higher frequencies.

[0081] Figure 5 Shows the variation diagram of the dielectric loss of the Sr / Co co-doped CCTO giant dielectric ceramic samples prepared in Examples 1-4 of the present invention with temperature at a specific frequency. From Figure 5 it can be seen that in the temperature range of 30°C - 210°C, as the temperature increases, the loss shows an upward trend in the frequency range of 100 Hz - 100 kHz. At lower frequencies, as the test temperature increases, the dielectric loss of all samples increases significantly, which can be explained by the DC conduction mechanism related to the grains. And as the frequency increases, the rise becomes gentler and gentler, indicating that in this temperature range, thermally activated processes such as interfacial polarization start to work, the loss is relatively stable at lower temperatures, at higher temperatures, the change amplitude at low frequencies increases significantly, and it remains stable at higher frequencies, which is closely related to the change trend of the dielectric constant. And Table 1 shows the dielectric loss values of the Sr / Co co-doped CCTO giant dielectric ceramic samples in the frequency bands prepared in Examples 1-4 of the present invention.

[0082] Table 1

[0083]

[0084] From Table 1, Figures 3 - 5 it can be seen that the Sr / Co co-doped CCTO giant dielectric ceramic provided by the present invention has both a giant dielectric constant, low dielectric loss, excellent temperature stability, and excellent comprehensive performance, and is a high-performance giant dielectric ceramic material.

[0085] In summary, the present invention provides a preparation method and application of Sr / Co co-doped CCTO giant dielectric ceramic. In the present invention, using Sr 2+ ions to replace and dope the Ca 2+ ion sites can effectively increase the grain boundary resistance and the height of the Schottky barrier, and can enhance the dielectric relaxation characteristics. By using Co 2+ ions to replace and dope the Cu 2+ ion sites, CaTiO3 and Co2TiO4 phases will be formed at the grain boundaries, realizing the reduction of the Cu-rich phase, thereby reducing the grain boundary resistivity and dielectric loss, and achieving the effect of effectively regulating the dielectric properties of the ceramic. The dielectric constant of the CSCCTO giant dielectric ceramic material provided by the present invention can reach 10 4 or more, and the dielectric loss can be as low as 0.04.

[0086] It should be noted that, for the foregoing embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps may be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on these embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still, without conflict, make combinations, additions, deletions or other adjustments to the features in the embodiments of the present invention according to the circumstances without creative efforts, so as to obtain different technical solutions that are essentially not divorced from the concept of the present invention, and these technical solutions also belong to the scope of protection of the present invention.

Claims

1. Preparation method of Sr / Co co-doped CCTO giant dielectric ceramics, characterized in that, The method includes: S10. Take the powder raw materials for preparing the co-doped CCTO giant dielectric ceramic. The powder raw materials include CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder. After proportioning the CaCO3 powder, CuO powder, TiO2 powder, SrCO3 powder, and CoO powder according to the stoichiometric ratio, add alcohol, and perform primary ball milling on the powder raw materials. After the ball milling is completed, dry to obtain the precursor powder. S20. Take the precursor powder, perform pre-sintering on the precursor powder to obtain the pre-sintered powder, and reserve it for use. S30. Obtain the pre-sintered powder, perform secondary ball milling on the pre-sintered powder, and perform drying treatment on the pre-sintered powder after the secondary ball milling to obtain the ceramic powder, and reserve it for use. S40. Take the ceramic powder, perform tabletting on the ceramic powder to obtain the green body, and reserve it for use. S50. Take the green body, and sinter the green body to obtain the Sr / Co co-doped CCTO giant dielectric ceramic material.

2. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 1, characterized in that: In step S10, the particle size of the powder raw materials is less than 250 nm. When performing primary ball milling on the powder raw materials, zirconia balls are used as the grinding balls, anhydrous ethanol is used as the ball milling medium, the mass ratio of the powder raw materials to the zirconia balls is 1:2.5 - 3, the mass ratio of the anhydrous ethanol to the powder raw materials is 1:1.1 - 1.3, the primary ball milling speed is 450 - 500 r / min, and the primary ball milling time is 12 - 24 h.

3. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 1, characterized in that: In step S20, when performing pre-sintering on the precursor powder, the pre-sintering temperature is 900 - 1000 °C, the heating rate from room temperature to the pre-sintering temperature is 3 - 5 °C / min, and the pre-sintering time is 8 - 10 h.

4. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 3, characterized in that: In step S30, the speed of the secondary ball milling is 450 - 550 r / min, and the time of the secondary ball milling is 12 - 20 h.

5. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 4, characterized in that: In step S40, when performing tabletting on the ceramic powder, the tabletting method adopts the first forming method or the second forming method.

6. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 5, characterized in that: The first forming method includes: Take the ceramic powder, perform pre-pressing and cold isostatic pressing on the ceramic powder in sequence. The temperature of the cold isostatic pressing is room temperature, the pressure of the cold isostatic pressing is 200 - 250 MPa, and the time of the cold isostatic pressing is 2 - 5 min.

7. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 6, characterized in that: The second forming method includes: Take the ceramic powder, mix the ceramic powder with a binder and granulate to obtain powder particles. Perform pressing on the obtained powder particles or perform pre-pressing and cold isostatic pressing on the obtained powder particles in sequence. When adopting the second forming method, degumming of the obtained green body is also included before sintering. The temperature of the degumming is 500 - 550 °C, and the heat preservation time is 6 - 9 h.

8. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 5, characterized in that: In step S50, the sintering temperature of the green body is 1050 - 1100 °C, and the heat preservation time of the sintering is 8 - 10 h.

9. The preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to claim 1, characterized in that: The chemical composition of the Sr / Co co-doped CCTO giant dielectric ceramic material is Ca 1-x Sr x Cu 3-y Co y Ti4O 12 .

10. Application of the preparation method of the Sr / Co co-doped CCTO giant dielectric ceramic according to any one of claims 1 - 9 in a dielectric capacitor.

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