Calcium-doped barium titanate powder, and preparation method and application thereof

Abstract

The application belongs to the technical field of nano ceramic powder preparation, discloses a calcium-doped barium titanate powder and a preparation method and application thereof, and aims to solve the technical problems of needing a mineralizer in the preparation process of the calcium-doped barium titanate powder, large particle size of the prepared powder, uneven element doping, poor dispersibility and low tetragonal phase content. The steps are as follows: (1) preparing a barium salt solution containing a calcium source; (2) taking anatase titanium dioxide obtained by calcining titanium nanotubes as a titanium source, and adding the titanium source into the barium salt solution containing the calcium source to obtain a calcium-doped barium titanate precursor solution; (3) performing hydrothermal reaction on the precursor solution; (4) performing filtration, washing, drying and grinding to obtain the calcium-doped barium titanate powder. The calcium-doped barium titanate powder prepared by the application has the characteristics of small particle size, narrow distribution, good dispersibility and high tetragonal phase content. Meanwhile, the reaction can avoid using a large amount of mineralizer, the method has low cost, good safety, simple process, can realize large-scale production of the powder, and meets the development requirements of subsequent high-temperature, thin-layer multi-layer ceramic capacitor products.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of nano-ceramic powder preparation, and particularly relates to a calcium-doped barium titanate powder, a preparation method and application thereof. BACKGROUND

[0002] Barium titanate is an important basic raw material for multilayer ceramic capacitors (MLCC) due to its high dielectric properties, environmental friendliness, and non-toxicity. With the development of MLCC towards miniaturization, large capacity, and high reliability, higher requirements are put forward for the structural parameters of barium titanate, such as particle size, dispersibility, and tetragonal phase.

[0003] In addition, the dielectric constant of barium titanate ceramic changes greatly with temperature, and near the Curie temperature, the dielectric constant will change abruptly, which is manifested as a very sharp Curie peak, wide hysteresis loop, and low breakdown strength, limiting its wide application in energy storage capacitors. Barium titanate is a perovskite structure of ABO3, and by doping different metal elements into the Ba site or Ti site in the lattice, the high-temperature temperature stability can be improved. Appropriate calcium doping can move the Curie temperature of BaTiO3 to a higher temperature, expand the temperature range of the tetragonal phase, broaden the Curie peak, and improve the temperature stability. The entry of calcium into the barium titanate lattice not only effectively reduces the grain size to improve the energy storage performance, but also improves the stability of the ceramic in a high-pressure environment, while reducing the dielectric loss.

[0004] Currently, solid phase method and liquid phase method are commonly used to synthesize calcium-doped barium titanate powder. The solid phase method has the advantages of abundant and easily available raw materials, simple and convenient process, low production cost, and mature technology. However, the synthesized powder has large particle size, serious particle agglomeration, poor dispersibility, and the reaction needs to be carried out at high temperature, consuming a lot of energy. Zhang Lei et al. used a rotary furnace low-high speed two-stage calcination solid phase method to synthesize calcium-doped barium titanate powder. Compared with the traditional one-stage high-temperature solid phase calcination, the obtained calcium-doped barium titanate has uniform particle size and high tetragonality, but the average particle size is 1.32 um, which is relatively large. Zhu Guisheng et al. synthesized calcium-doped barium titanate powder with an average particle size of about 100 nm and good dispersibility by hydrothermal method, but the reaction needs to be assisted by high-concentration KOH as a mineralizer, and a large amount of water washing is needed to wash the alkaline mineralizer, which may cause the residual of trace amounts of alkaline or alkaline earth metal ions in the barium titanate body and cannot be applied to the field of high-purity electronic materials. Since H2TiO3 is used as the titanium source, it contains a large amount of hydroxyl groups in its structure, and the calcium-doped barium titanate powder prepared by it has high hydroxyl defect and low tetragonal phase content (c / a = 1.0036), which cannot meet the actual application requirements. SUMMARY

[0005] In order to solve the technical problems of large particle size, wide distribution, poor dispersibility of calcium-doped barium titanate prepared by the solid phase method in the prior art, high defect content and low tetragonal phase content of the calcium-doped barium titanate prepared by the liquid phase method, and the need for a large amount of mineralizer, the application provides a calcium-doped barium titanate powder, a preparation method and application thereof, and the calcium-doped barium titanate powder with small size, high dispersibility and high tetragonal phase content is prepared, and no mineralizer is needed in the preparation process and the process is simple.

[0006] In order to achieve the above-mentioned purposes, the technical scheme of the application is as follows:

[0007] A preparation method of a calcium-doped barium titanate powder, steps are as follows:

[0008] (1) a barium salt solution with a certain concentration is prepared, heated and dissolved, and after complete dissolution, a proper amount of a calcium source is added after cooling;

[0009] (2) a titanium source is weighed according to a certain barium-calcium molar ratio and added to the barium salt solution containing the calcium, and high-speed emulsification shearing is performed to obtain a calcium-doped barium titanate precursor solution;

[0010] (3) the calcium-doped barium titanate precursor solution is transferred to a high-temperature reaction kettle for hydrothermal reaction to obtain a barium titanate suspension;

[0011] (4) the calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying and grinding to obtain the calcium-doped barium titanate powder.

[0012] In the step (1), the barium source in the barium salt solution is Ba(OH)2·8H2O, the solvent is deionized water, and the concentration of the barium salt solution is 2-3 mol / L.

[0013] In the step (1), the temperature for heating and dissolving the barium salt solution is 70-90 DEG C, and after complete dissolution, the temperature is cooled to 40-50 DEG C.

[0014] In the step (1), the calcium source is one or a mixture of two or more of CaCl2, Ca(NO3)2, Ca(CH3COO)2 and Ca(H2PO4)2.

[0015] In the step (1), the molar ratio of the calcium source to the barium source is (1-10):(90-99).

[0016] In the step (2), the titanium source is anatase titanium dioxide formed after nanotube titanium oxide (NTA) is treated at 300-700 DEG C for 0.5-8 h.

[0017] In the step (2), the molar ratio of (barium source+calcium source) to the titanium source is (1.0-1.2):1.

[0018] The temperature of the hydrothermal reaction in the step (3) is 160-200 DEG C, and the time is 8-48h.

[0019] The calcium-doped barium titanate powder prepared by the preparation method.

[0020] Application of the calcium-doped barium titanate powder in a multilayer ceramic capacitor.

[0021] The present application has the following advantages:

[0022] (1) The titanium nanotube (H2Ti2O4(OH)2, NTA) in the present application has a one-dimensional tubular structure, and is converted into anatase titanium dioxide after high-temperature calcination. The anatase titanium dioxide has the characteristics of small particle size, high dispersibility, and high oxygen vacancy content in the structure, which affects the Ti-O bond length around the vacancy, changes the local coordination environment, and produces a reduced surface, all of which are conducive to improving the reactivity of the titanium dioxide. The titanium dioxide also has the characteristics of uniform size distribution, which keeps the dissolution-nucleation rate relatively consistent. When the titanium dioxide is used as a titanium source for preparing calcium-doped barium titanate by a hydrothermal method, it has good reactivity, and the reaction process is mild and easy to control. The prepared calcium-doped barium titanate has the advantages of small particle size (average particle size ≤100 nm), high dispersibility, uniform calcium element distribution, and high tetragonal phase content.

[0023] (2) The present application uses the anatase titanium dioxide obtained by heat treatment of the titanium nanotube as a titanium source, which has high reactivity in the hydrothermal process, avoids the use of high-concentration inorganic alkali mineralizers, and on the one hand reduces the subsequent large amount of water washing process, and on the other hand avoids the residual of trace amounts of alkaline or alkaline earth metal ions in the barium titanate body, thereby meeting the purity requirements of MLCC for raw materials.

[0024] (3) The preparation method proposed in the present application avoids the problems of high energy consumption caused by high-temperature calcination in the solid-phase method, large particle size of the prepared powder, and serious particle agglomeration. The method also avoids the problem of using mineralizers in the traditional liquid-phase preparation process. The method has the advantages of low cost, good safety, simple process, and can realize large-scale production of the powder, and meets the development requirements of subsequent high-temperature, thin-layer multilayer ceramic capacitors. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1The images show the XRD pattern (a), SEM pattern (b), and ESR spectrum (c) of the titanium dioxide source used in Example 1 of this invention.

[0027] Figure 2 The images show SEM images (a), particle size distribution (b), and elemental distribution (c) of the calcium-doped barium titanate powder prepared in Example 1 of this invention.

[0028] Figure 3 This is a SEM image of calcium-doped barium titanate prepared using titanate nanotubes as the titanium source in Comparative Example 1 of this invention.

[0029] Figure 4 The images shown are SEM images of the calcium-doped barium titanate powders prepared in Examples 2-4 of this invention, where (a) Example 2; (b) Example 3; and (c) Example 4.

[0030] Figure 5 The images show the XRD patterns of the calcium-doped barium titanate powders prepared in Examples 1-4 of this invention.

[0031] Figure 6 SEM images and corresponding particle size distribution diagrams of calcium-doped barium titanate powders with different calcium contents prepared according to the present invention are shown, wherein (a) Example 5; (b) Example 6; (c) Example 7; (d) Example 8; (d) Example 9. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] The titanate nanotubes used in this invention are prepared as follows: TiO2 is dispersed in 80 mL of 10 M NaOH solution, stirred evenly, and then placed in a polytetrafluoroethylene hydrothermal reactor. The reactor is reacted at 120 °C for 24 h to prepare Na2Ti2O5·H2O. The Na2Ti2O5·H2O is then washed with water until pH = 10, and then acid-washed with HCl solution (pH = 1.0) until pH = 1.2. The mixture is stirred for 4-5 h, and then washed again with water to remove Cl. - After reaching neutrality, filter under vacuum and finally dry in a vacuum oven at 60℃. The resulting product is titanium dioxide nanotubes (H2Ti2O5·H2O), abbreviated as NTA.

[0034] Example 1

[0035] The preparation method of calcium-doped barium titanate powder in this embodiment includes the following steps:

[0036] (1) A certain amount of titanium nanotube is placed in a muffle furnace and heat treated at 600°C for 2h to obtain anatase titanium dioxide.

[0037] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution. The solution is heated to 85°C and stirred until completely dissolved. The solution is then naturally cooled to 45°C, and Ca(CH3COO)2 is added. The molar ratio of the barium source to the calcium source is controlled to be 95:5.

[0038] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt. The molar ratio of the (Ba source + Ca source) to the Ti source is controlled to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0039] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle and hydrothermally reacted at 200°C for 48h. The solution is then cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0040] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0041] Figure 1 The structure characterization graph of the titanium dioxide titanium source used in this example. From Figure 1 a The XRD graph shows that the titanium dioxide titanium source is an anatase crystal structure, Figure 1 b The SEM graph shows that the titanium dioxide particles are composed of small particles with a size of 20-50 nm, and the particles are uniformly dispersed, from Figure 1 c It can be seen that the structure is rich in bound single-electron oxygen vacancies, which are beneficial to improve the reactivity.

[0042] Figure 2 The SEM graph, particle size distribution graph, and element distribution graph of the calcium-doped barium titanate powder prepared in this example. Figure 2 a and Figure 2 b are the SEM graph and particle size distribution graph of the prepared powder, respectively. It can be seen that the average particle size of the calcium-doped barium titanate powder prepared under the preparation process conditions is about 97 nm, the particle size is uniform, the distribution is narrow, and the dispersibility is good. Figure 2 c is the element distribution graph of the calcium-doped barium titanate powder. From the graph, it can be seen that the calcium element is uniformly distributed in the barium titanate.

[0043] Example 2

[0044] A method for preparing a calcium-doped barium titanate powder is provided in this example, and the steps are as follows:

[0045] (1) A certain amount of titanate nanotubes is placed in a muffle furnace and heat treated at 300°C for 2h to obtain anatase titanium dioxide.

[0046] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution. The solution is heated to 85°C and stirred until completely dissolved. After natural cooling to 45°C, Ca(CH3COO)2 is added. The molar ratio of the barium source to the calcium source is controlled to be 95:5.

[0047] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt. The molar ratio of (Ba source + Ca source) to Ti source is controlled to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0048] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle. After hydrothermal reaction at 200°C for 48h, the solution is cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0049] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0050] Example 3

[0051] The preparation method of a calcium-doped barium titanate powder in this example is as follows:

[0052] (1) A certain amount of titanate nanotubes is placed in a muffle furnace and heat treated at 400°C for 2h to obtain anatase titanium dioxide.

[0053] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution. The solution is heated to 85°C and stirred until completely dissolved. After natural cooling to 45°C, Ca(CH3COO)2 is added. The molar ratio of the barium source to the calcium source is controlled to be 95:5.

[0054] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt. The molar ratio of (Ba source + Ca source) to Ti source is controlled to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0055] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle. After hydrothermal reaction at 200°C for 48h, the solution is cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0056] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying, and grinding to obtain the calcium-doped barium titanate powder.

[0057] Example 4

[0058] The preparation method of the calcium-doped barium titanate powder of the present example comprises the following steps:

[0059] (1) A certain amount of titanic nanotubes is placed in a muffle furnace and heat treated at 700°C for 2h to obtain anatase titanium dioxide.

[0060] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution. After being heated to 85°C and completely dissolved, the solution is naturally cooled to 45°C, and Ca(CH3COO)2 is added. The molar ratio of the barium source and the calcium source is controlled to be 95:5.

[0061] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt. The molar ratio of (Ba source + Ca source) to Ti source is controlled to be 1.06:1. High-speed shearing is performed at 1000rpm for 3min to obtain a calcium-doped barium titanate precursor solution.

[0062] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle. After hydrothermal reaction at 200°C for 48h, the solution is cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0063] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying, and grinding to obtain the calcium-doped barium titanate powder.

[0064] Example 5

[0065] The preparation method of the calcium-doped barium titanate powder of the present example comprises the following steps:

[0066] (1) A certain amount of titanic nanotubes is placed in a muffle furnace and heat treated at 600°C for 2h to obtain anatase titanium dioxide.

[0067] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution. After being heated to 85°C and completely dissolved, the solution is naturally cooled to 45°C, and Ca(CH3COO)2 is added. The molar ratio of the barium source and the calcium source is controlled to be 99:1.

[0068] (3) Add the titanium source prepared in step (1) to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2solution, and control the molar ratio of (Ba source + Ca source) to Ti source to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0069] (4) Transfer the calcium-doped barium titanate precursor solution to a high-pressure reaction kettle, and after hydrothermal reaction at 220°C for 24 h, cool to room temperature to obtain a calcium-doped barium titanate suspension.

[0070] (5) Perform suction filtration, deionized water washing, drying, and grinding on the calcium-doped barium titanate suspension to obtain a calcium-doped barium titanate powder.

[0071] Example 6

[0072] A method for preparing a calcium-doped barium titanate powder according to the present embodiment is as follows:

[0073] (1) Weigh a certain amount of titanate nanotubes and place them in a muffle furnace for heat treatment at 600°C for 2 h to obtain anatase titanium dioxide.

[0074] (2) Weigh high-purity Ba(OH)2·8H2O, add deionized water to prepare a 2.5M Ba(OH)2·8H2O solution, and after stirring and heating to 85°C until complete dissolution, naturally cool to 45°C, and then add Ca(CH3COO)2, and control the molar ratio of the barium source and the calcium source to be 98:2.

[0075] (3) Add the titanium source prepared in step (1) to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2solution, and control the molar ratio of (Ba source + Ca source) to Ti source to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0076] (4) Transfer the calcium-doped barium titanate precursor solution to a high-pressure reaction kettle, and after hydrothermal reaction at 220°C for 24 h, cool to room temperature to obtain a calcium-doped barium titanate suspension.

[0077] (5) Perform suction filtration, deionized water washing, drying, and grinding on the calcium-doped barium titanate suspension to obtain a calcium-doped barium titanate powder.

[0078] Example 7

[0079] A method for preparing a calcium-doped barium titanate powder according to the present embodiment is as follows:

[0080] (1) Weigh a certain amount of titanate nanotubes and place them in a muffle furnace for heat treatment at 600°C for 2 h to obtain anatase titanium dioxide.

[0081] (2) Weigh high-purity Ba(OH)2·8H2O, add deionized water to prepare 2.5M Ba(OH)2·8H2O, stir and heat to 85°C until completely dissolved, then naturally cool to 45°C, and then add Ca(CH3COO)2, controlling the molar ratio of barium source and calcium source to be 97:3.

[0082] (3) Add the titanium source prepared in step (1) to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2 solution, and control the molar ratio of (Ba source + Ca source) to Ti source to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0083] (4) Transfer the calcium-doped barium titanate precursor solution to a high-pressure reaction kettle, hydrothermally react at 220°C for 24h, and then cool to room temperature to obtain a calcium-doped barium titanate suspension.

[0084] (5) Perform suction filtration, deionized water washing, drying, and grinding on the calcium-doped barium titanate suspension to obtain a calcium-doped barium titanate powder.

[0085] Example 8

[0086] A method for preparing a calcium-doped barium titanate powder according to the present embodiment is as follows:

[0087] (1) Weigh a certain amount of titanate nanotubes and place them in a muffle furnace for heat treatment at 600°C for 2h to obtain anatase titanium dioxide.

[0088] (2) Weigh high-purity Ba(OH)2·8H2O, add deionized water to prepare 2.5M Ba(OH)2·8H2O, stir and heat to 85°C until completely dissolved, then naturally cool to 45°C, and then add Ca(CH3COO)2, controlling the molar ratio of barium source and calcium source to be 96:4.

[0089] (3) Add the titanium source prepared in step (1) to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2 solution, and control the molar ratio of (Ba source + Ca source) to Ti source to be 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0090] (4) Transfer the calcium-doped barium titanate precursor solution to a high-pressure reaction kettle, hydrothermally react at 220°C for 24h, and then cool to room temperature to obtain a calcium-doped barium titanate suspension.

[0091] (5) Perform suction filtration, deionized water washing, drying, and grinding on the calcium-doped barium titanate suspension to obtain a calcium-doped barium titanate powder.

[0092] Example 9

[0093] A preparation method of the calcium-doped barium titanate powder of the embodiment is as follows:

[0094] (1) A certain amount of titanic nanotubes was placed in a muffle furnace and heat-treated at 600 DEG C for 2h to obtain anatase titanium dioxide.

[0095] (2) High-purity Ba(OH)2·8H2O was weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution, which was heated to 85 DEG C and stirred until completely dissolved, and then naturally cooled to 45 DEG C, and then Ca(CH3COO)2 was added, and the molar ratio of the barium source and the calcium source was controlled to be 90:10.

[0096] (3) The titanium source prepared in step (1) was added to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2 solution, and the molar ratio of the (Ba source+Ca source) / Ti source was controlled to be 1.06:1, and high-speed shearing was performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0097] (4) The calcium-doped barium titanate precursor solution was transferred to a high-pressure reaction kettle, and after hydrothermal reaction at 220 DEG C for 24h, it was cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0098] (5) The calcium-doped barium titanate suspension was subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0099] Example 10

[0100] A preparation method of the calcium-doped barium titanate powder of the embodiment is as follows:

[0101] (1) A certain amount of titanic nanotubes was placed in a muffle furnace and heat-treated at 600 DEG C for 2h to obtain anatase titanium dioxide.

[0102] (2) High-purity Ba(OH)2·8H2O was weighed and added to deionized water to prepare a 2.5M Ba(OH)2·8H2O solution, which was heated to 85 DEG C and stirred until completely dissolved, and then naturally cooled to 45 DEG C, and then Ca(CH3COO)2 was added, and the molar ratio of the barium source and the calcium source was controlled to be 90:10.

[0103] (3) The titanium source prepared in step (1) was added to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2 solution, and the molar ratio of the (Ba source+Ca source) / Ti source was controlled to be 1.06:1, and high-speed shearing was performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0104] (4) The calcium-doped barium titanate precursor solution was transferred to a high-pressure reaction kettle, and after hydrothermal reaction at 220 DEG C for 24h, it was cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0105] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying and grinding to obtain the calcium-doped barium titanate powder.

[0106] Example 11

[0107] The preparation method of the calcium-doped barium titanate powder of the present example comprises the following steps:

[0108] (1) A certain amount of titanic nanotubes is placed in a muffle furnace and heat treated at 300°C for 8h to obtain anatase titanium dioxide.

[0109] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 3M Ba(OH)2·8H2O solution. After being heated to 90°C and completely dissolved, the solution is naturally cooled to 50°C. Then, Ca(NO3)2 is added, and the molar ratio of the barium source to the calcium source is controlled to be 95:5.

[0110] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt, and the molar ratio of the (Ba source + Ca source) to the Ti source is controlled to be 1.2:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0111] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle, and hydrothermal reaction is performed at 200°C for 48h. After being cooled to room temperature, a calcium-doped barium titanate suspension is obtained.

[0112] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying and grinding to obtain the calcium-doped barium titanate powder.

[0113] Example 12

[0114] The preparation method of the calcium-doped barium titanate powder of the present example comprises the following steps:

[0115] (1) A certain amount of titanic nanotubes is placed in a muffle furnace and heat treated at 600°C for 2h to obtain anatase titanium dioxide.

[0116] (2) High-purity Ba(OH)2·8H2O is weighed and added to deionized water to prepare a 2M Ba(OH)2·8H2O solution. After being heated to 70°C and completely dissolved, the solution is naturally cooled to 40°C. Then, CaCl2 is added, and the molar ratio of the barium source to the calcium source is controlled to be 95:5.

[0117] (3) The titanium source prepared in step (1) is added to the prepared Ba(OH)2·8H2O solution containing calcium salt, and the molar ratio of the (Ba source + Ca source) to the Ti source is controlled to be 1.2:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0118] (4) The calcium-doped barium titanate precursor solution was transferred to a high-pressure reaction kettle, and after hydrothermal reaction at 220°C for 8h, it was cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0119] (5) The calcium-doped barium titanate suspension was subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0120] Example 13

[0121] The preparation method of a calcium-doped barium titanate powder in this example is as follows:

[0122] (1) A certain amount of titania nanotubes was placed in a muffle furnace and heat-treated at 600°C for 2h to obtain anatase titanium dioxide.

[0123] (2) High-purity Ba(OH)2·8H2O was weighed, deionized water was added to prepare a 2M Ba(OH)2·8H2O solution, and after stirring and heating to 70°C until complete dissolution, the solution was naturally cooled to 40°C, and CaCl2 was added, with the molar ratio of barium source to calcium source controlled at 95:5.

[0124] (3) The titanium source prepared in step (1) was added to the prepared Ba(OH)2·8H2O solution containing calcium salt, and the molar ratio of (Ba source + Ca source) to Ti source was controlled at 1.06:1. High-speed shearing was performed at 1000rpm for 3min to obtain a calcium-doped barium titanate precursor solution.

[0125] (4) The calcium-doped barium titanate precursor solution was transferred to a high-pressure reaction kettle, and after hydrothermal reaction at 160°C for 48h, it was cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0126] (5) The calcium-doped barium titanate suspension was subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0127] Comparative Example 1

[0128] The preparation method of a calcium-doped barium titanate powder in this example is as follows:

[0129] (1) The titania nanotubes were not subjected to temperature treatment.

[0130] (2) High-purity Ba(OH)2·8H2O was weighed, deionized water was added to prepare a 2.5M Ba(OH)2·8H2O solution, and after stirring and heating to 85°C until complete dissolution, the solution was naturally cooled to 45°C, and Ca(CH3COO)2 was added, with the molar ratio of barium source to calcium source controlled at 95:5.

[0131] (3) Add the titanium source prepared in step (1) to the prepared Ba(OH)2·8H2O and Ca(CH3COO)2 solution, and control the molar ratio of (Ba source + Ca source) to Ti source at 1.06:1. High-speed shearing is performed at 1000 rpm for 3 min to obtain a calcium-doped barium titanate precursor solution.

[0132] (4) The calcium-doped barium titanate precursor solution is transferred to a high-pressure reaction kettle, and after hydrothermal reaction at 200°C for 48 h, it is cooled to room temperature to obtain a calcium-doped barium titanate suspension.

[0133] (5) The calcium-doped barium titanate suspension is subjected to suction filtration, deionized water washing, drying, and grinding to obtain a calcium-doped barium titanate powder.

[0134] Figure 3 The calcium-doped barium titanate powder prepared for the present comparative example can be seen from the figure. The calcium-doped barium titanate prepared using NTA as the titanium source has incomplete particle growth, and the particle size agglomeration is relatively serious.

[0135] Test Example

[0136] The prepared barium titanate powder is subjected to performance testing. Scanning electron microscopy (SEM) is used to observe the grain size; XRD testing is used to obtain the powder tetragonality c / a. A nanoparticle size and zeta potential analyzer is used to characterize the synthesized powder, and the inhomogeneity coefficient MD=(D 90 -D 10 ) / D 50 is obtained. The smaller the MD, the more uniform the sample. The effects of heat treatment of the titanate nanotubes and the calcium content on the performance of the calcium-doped barium titanate powder are investigated.

[0137] (1) The effects of different heat treatments of the titanate nanotubes on the performance of the calcium-doped barium titanate powder, and the results are shown in Figure 4 、 Figure 5 and Table 1.

[0138] Figure 4 The scanning electron micrograph of the calcium-doped barium titanate powder prepared in Examples 2-4 can be seen from the figure. When the heat treatment temperature is 300°C, 400°C, and 700°C, the average particle size of the prepared calcium-doped barium titanate powder is 95 nm, 100 nm, and 88 nm, respectively. The particle size is uniform, the distribution is narrow, and the dispersibility is good.

[0139] Figure 5 The XRD pattern of the calcium-doped barium titanate powder prepared in Example 1-4 can be seen from the figure. The characteristic peaks of the pure-phase barium titanate are obtained, and no impurity peaks appear, which indicates that calcium has entered the barium titanate lattice to form a solid solution.

[0140] Table 1 Effects of different heat treatments of the titanium source on the performance of the calcium-doped barium titanate powder

[0141]

[0142] As can be seen from Table 1, the calcium-doped barium titanate prepared from titanium dioxide obtained by calcining NTA at 600℃ for 2 hours has a high tetragonal phase content and a low non-uniformity coefficient. Therefore, 600℃ is the optimal calcination temperature.

[0143] (2) The effect of different barium source / calcium source molar ratios on the properties of calcium-doped barium titanate powder is shown in the figure. Figure 6 As shown in Table 2.

[0144] Figure 6 The images show scanning electron microscope (SEM) images of the calcium-doped barium titanate powders prepared in Examples 5-9 and their corresponding particle size distributions. As can be seen from the images, the synthesized powder particles are small in size and have a relatively uniform particle size distribution.

[0145] Table 2. Effect of barium source / calcium source molar ratio on the properties of calcium-doped barium titanate powder

[0146] Example Molar ratio of barium source / calcium source c / a MD Example 1 95：5 1.0074 0.723 Example 5 99：1 1.0073 0.931 Example 6 98：2 1.0072 1.156 Example 7 97：3 1.0069 0.732 Example 8 96：4 1.0070 0.979 Example 9 90：10 1.0072 0.986

[0147] As can be seen from Table 2, when the molar ratio of barium source to calcium source is 95:5, it exhibits a higher tetragonal phase content and a lower inhomogeneity coefficient.

[0148] In summary, this invention proposes a method for preparing calcium-doped barium titanate powder without the need for mineralizers. When using titanium dioxide obtained from the high-temperature calcination of titanate nanotubes as the titanium source for the hydrothermal preparation of calcium-doped barium titanate, the small particle size, high dispersibility, and high oxygen vacancy content of this titanium dioxide successfully produce calcium-doped barium titanate powder with small, uniform particle size, narrow distribution, good dispersibility, and a high tetragonal phase content. This invention avoids the use of high-concentration inorganic alkali mineralizers, thus avoiding extensive water washing processes and the residue of alkaline ions in the calcium-doped barium titanate powder, meeting the high purity requirements of powder materials for electronic components.

[0149] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a calcium-doped barium titanate powder, characterized by, The steps are as follows: (1) adding a calcium source into a barium salt solution with a concentration of 2-3 mol / L to obtain a barium salt solution containing calcium; wherein the barium salt is Ba(OH)2·8H2O; (2) taking the heat-treated titanate nanotube as a titanium source, and adding the titanium source into the barium salt solution containing calcium prepared in step (1) according to a molar ratio of (calcium source + barium source) / titanium source to obtain a calcium-doped barium titanate precursor solution; wherein the heat treatment is performed at a temperature of 300-700 ℃ for 0.5-8 h; (3) obtaining a calcium-doped barium titanate suspension by subjecting the calcium-doped barium titanate precursor solution obtained in step (2) to a hydrothermal reaction; wherein the hydrothermal reaction is performed at a temperature of 160-200 ℃ for 8-48 h; (4) obtaining a calcium-doped barium titanate powder by subjecting the calcium-doped barium titanate suspension obtained in step (3) to suction filtration, deionized water washing, drying, and grinding.

2. The method for preparing calcium-doped barium titanate powder according to claim 1, characterized in that, In step (1), the solvent in the barium salt solution is deionized water.

3. The method for preparing calcium-doped barium titanate powder according to claim 2, characterized in that, In step (1), the calcium source is one or a mixture of two or more of CaCl2, Ca(NO3)2, Ca(CH3COO)2, and Ca(H2PO4)2; and the molar ratio of the calcium source to the barium source is (1-10):(90-99).

4. The method of claim 3, wherein the calcium-doped barium titanate powder is prepared by the steps of: preparing a barium titanate powder; and mixing the barium titanate powder with a calcium compound. In step (2), the molar ratio of (barium source + calcium source) / titanium source is (1.0-1.2):

1.

5. The calcium-doped barium titanate powder prepared by the preparation method of any one of claims 1-4.

6. The use of the calcium-doped barium titanate powder of claim 5 in a multilayer ceramic capacitor.

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