A tetragonal phase nano-barium titanate powder, a preparation method and application thereof

Abstract

The application provides a tetragonal phase nano-barium titanate powder, a preparation method and application thereof, and belongs to the technical field of inorganic non-metallic nanometer materials. A titanium source, a barium source, a composite molten salt, an inorganic base and water are mixed and dried to obtain a mixture, and then the mixture is calcined to obtain the tetragonal phase nano-barium titanate powder; the titanium source is one or more of amorphous titanium precursor, anatase titanium dioxide and rutile titanium dioxide; the composite molten salt comprises a soluble barium salt and an auxiliary molten salt; and the soluble barium salt is barium chloride and / or barium fluoride. The results of the examples show that the structure of the tetragonal phase nano-barium titanate powder prepared by the application is a tetragonal phase crystal structure, the tetragonal phase content is greater than or equal to 80%, the c / a axial ratio is greater than or equal to 1.008, the average particle size is 50-300 nm, the residual chlorine content is less than 0.1 wt%, the Ba / Ti molar ratio is 0.99-1.05, the particle size distribution is uniform, the crystallinity is high, and the dispersibility is good.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic nanomaterials technology, and in particular to a tetragonal phase barium titanate nanopowder, its preparation method, and its application. Background Technology

[0002] Barium titanate (BaTiO3) is a typical perovskite-type ferroelectric material with excellent ferroelectric, piezoelectric, dielectric, and insulating properties. It is widely used in the electronic ceramics industry, including multilayer ceramic capacitors (MLCCs), ferroelectric non-volatile memories, and piezoelectric sensors. Tetragonal barium titanate, due to its spontaneous polarization characteristics, exhibits superior dielectric and ferroelectric properties compared to the cubic phase, making it a core material for manufacturing high-performance MLCCs.

[0003] With the miniaturization, integration, and high performance of electronic components, the demand for tetragonal barium titanate nanoparticles is becoming increasingly urgent. Currently, the main methods for preparing barium titanate powder include solid-state methods, co-precipitation methods, sol-gel methods, hydrothermal methods, and molten salt methods. Solid-state methods typically require temperatures above 1000℃ to achieve the tetragonal phase transformation, resulting in coarse grains. While traditional hydrothermal or sol-gel methods can obtain nanoparticles, they often require a closed, high-pressure environment, and it is difficult to control the purity of the tetragonal phase. Molten salt methods, due to their ability to promote mass transfer and lower reaction temperatures in a liquid medium, show unique advantages in the synthesis of nanomaterials.

[0004] However, existing molten salt methods for preparing barium titanate still have shortcomings. For example, Zhang et al. (Powder Technology, 2012, 217:629-633) disclosed the synthesis of BaTiO3 nanoparticles at low temperatures of 600–900 °C using Ba(OH)₂·8H₂O as the barium source. However, this technique suffers from phase structure defects, with most products being cubic phases, lacking the tetragonal phase distortion required for ferroelectricity. Furthermore, traditional molten salt methods for preparing barium titanate also suffer from insufficient particle size control, failing to effectively address the kinetic control of grain growth at high temperatures, making it difficult to stably lock the particle size within the 50–300 nm range. This results in existing techniques either producing cubic phases with poor dielectric properties or necessitating forced phase transformation by increasing the temperature (>950 °C), leading to abnormal grain growth. Summary of the Invention

[0005] The purpose of this invention is to provide a tetragonal phase barium titanate nanopowder, its preparation method, and its application. The preparation method provided by this invention can significantly reduce the synthesis temperature of tetragonal phase barium titanate, and has strong adaptability to a wide temperature window. At the same time, it can effectively inhibit abnormal grain growth, achieve controllable nanoscale particle size, and the prepared tetragonal phase barium titanate nanopowder has high tetragonality and high purity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing tetragonal phase barium titanate nanopowder, comprising: mixing a titanium source, a barium source, a composite molten salt, an inorganic alkali and water and drying the mixture to obtain a mixture, and then calcining the mixture to obtain tetragonal phase barium titanate nanopowder; The titanium source is one or more of amorphous titanium precursor, peroxide titanium precursor gel, anatase titanium dioxide, and rutile titanium dioxide; the amorphous titanium precursor is obtained by hydrolysis of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the peroxide titanium precursor gel is obtained by precipitation-oxidation of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid. The composite molten salt comprises a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride and / or barium fluoride; The inorganic base is sodium hydroxide and / or potassium hydroxide.

[0007] Preferably, the barium source includes one or more of the anhydrous and hydrated forms of barium carbonate, barium nitrate, barium hydroxide, barium oxalate, and barium peroxide.

[0008] Preferably, the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:(1~1.3).

[0009] Preferably, the auxiliary molten salt includes one or more of sodium chloride, potassium chloride, lithium chloride, and calcium chloride.

[0010] Preferably, the mass ratio of the soluble barium salt to the auxiliary molten salt is 1:(0.5~10).

[0011] Preferably, the ratio of the total mass of the titanium source and the barium source to the mass of the composite molten salt is 1:(0.1~10).

[0012] Preferably, the molar ratio of the inorganic base to the barium source is (0.05~2):1.

[0013] Preferably, the calcination temperature is 650~1000℃, the calcination time is 1~6h, and the heating rate to the calcination temperature is 4~6℃ / min.

[0014] This invention provides tetragonal phase barium titanate nanopowder prepared by the preparation method described in the above technical solution.

[0015] This invention provides the application of the tetragonal phase barium titanate nanopowder described above in the field of electronic ceramics industry.

[0016] This invention provides a method for preparing tetragonal phase barium titanate nanoparticles, comprising: mixing a titanium source, a barium source, a composite molten salt, an inorganic alkali, and water, drying the mixture to obtain a mixture, and then calcining the mixture to obtain tetragonal phase barium titanate nanoparticles; wherein the titanium source is one or more of amorphous titanium precursor, peroxytitanium precursor gel, anatase titanium dioxide, and rutile titanium dioxide; the amorphous titanium precursor is obtained by hydrolysis of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the peroxytitanium precursor gel is obtained by precipitation-oxidation of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the composite molten salt comprises a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride and / or barium fluoride; and the inorganic alkali is sodium hydroxide and / or potassium hydroxide. This invention allows for the control of the microstructure of barium titanate by processing different titanium sources accordingly, thereby flexibly controlling the particle size of the final barium titanate product. For example, using an amorphous titanium precursor obtained by hydrolysis, the particle size of the prepared tetragonal phase barium titanate nanoparticles can be controlled within the range of <100 nm; using an amorphous titanium precursor obtained by precipitation-oxidation, the particle size of the prepared tetragonal phase barium titanate nanoparticles can be controlled within the range of 100~200 nm. This invention introduces sodium hydroxide or potassium hydroxide as an added inorganic base. Unlike Ba(OH)2, NaOH and KOH not only do not decompose or become ineffective within the calcination temperature range, but can also form a eutectic system with the molten salt, constructing a continuous, stable, and adjustable high-temperature alkaline molten salt environment. In this environment, OH... - It can act on the surface of titanium precursors, promoting the breaking and recombination of Ti-O bonds and inducing c-axis preferred distortion of titanium-oxygen octahedrons ([TiO6]). This interfacial chemical reaction driven by an externally added alkali fundamentally lowers the thermodynamic energy barrier for tetragonal phase formation, allowing the reaction to proceed efficiently at around 750℃ without relying on high-temperature thermal excitation. This invention uses barium chloride and / or barium fluoride as key components of the composite molten salt. In the molten state, the soluble barium salt dissociates to generate a large number of barium ions (Ba... 2+This invention enables the formation of a barium-rich ion adsorption layer on the surface of barium titanate grains. This adsorption layer alters the interfacial energy and mass transfer kinetics of the grain surface, effectively inhibiting grain boundary migration and mass transport, thereby hindering grain coalescence and growth during calcination. Therefore, even when calcined over a wide temperature range of 650–1000 °C, the resulting tetragonal barium titanate powder maintains a nanoscale particle size. The auxiliary molten salt used in this invention has a low eutectic point, which is beneficial for forming a stable molten salt liquid phase. This invention achieves tetragonal phase transformation through calcination to obtain tetragonal barium titanate, while the low calcination temperature significantly reduces energy consumption, demonstrating the energy-saving and consumption-reducing advantages of this invention. The results of the examples show that the tetragonal phase barium titanate nanopowder prepared by the preparation method provided by the present invention has a tetragonal phase crystal structure, a tetragonal phase content ≥80%, a c / a axis ratio ≥1.008, an average particle size of 50~300nm, a residual chlorine content of less than 0.1wt%, a Ba / Ti molar ratio of 0.99~1.05, uniform particle size distribution, high crystallinity, and good dispersibility. Attached Figure Description

[0017] Figure 1 This is a particle size distribution diagram of the amorphous titanium precursor in Example 1; Figure 2 SEM image of the tetragonal phase barium titanate nanoparticles prepared in Example 1; Figure 3 XRD pattern of tetragonal phase barium titanate nanoparticles prepared in Example 1; Figure 4 SEM image of the tetragonal phase barium titanate nanoparticles prepared in Example 2; Figure 5 XRD pattern of tetragonal phase barium titanate nanoparticles prepared in Example 2; Figure 6 SEM image of the tetragonal phase barium titanate nanoparticles prepared in Example 3; Figure 7 SEM image of the barium titanate nanoparticles prepared in Comparative Example 1; Figure 8 XRD pattern of barium titanate nanoparticles prepared in Comparative Example 1; Figure 9 SEM image of the barium titanate nanoparticles prepared in Comparative Example 3; Figure 10 The image shows the SEM image of the barium titanate nanoparticles prepared in Comparative Example 4. Detailed Implementation

[0018] This invention provides a method for preparing tetragonal phase barium titanate nanopowder, comprising: mixing a titanium source, a barium source, a composite molten salt, an inorganic alkali and water and drying the mixture to obtain a mixture, and then calcining the mixture to obtain tetragonal phase barium titanate nanopowder; The composite molten salt comprises a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride and / or barium fluoride; the inorganic base is sodium hydroxide and / or potassium hydroxide.

[0019] In this invention, the titanium source is one or more of amorphous titanium precursor, peroxy titanium precursor gel, anatase titanium dioxide, and rutile titanium dioxide; the amorphous titanium precursor is obtained by hydrolysis of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the peroxy titanium precursor gel is obtained by precipitation-oxidation of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid.

[0020] In this invention, the preferred method for preparing the amorphous titanium precursor is as follows: adding the raw material to deionized water, then hydrolyzing, and filtering to obtain the amorphous titanium precursor; the raw material is one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the hydrolysis temperature is preferably 80-110℃, more preferably 90-100℃; the hydrolysis time is preferably 3-10h, more preferably 5-6h; the hydrolysis is preferably carried out under stirring conditions. This invention does not impose any special limitations on the amount of raw material and deionized water used, which can be determined based on the technical knowledge of those skilled in the art. This invention does not impose any special limitations on the specific operation of adding the raw material to the deionized water, and methods such as dropwise addition are acceptable. This invention does not impose any special limitations on the stirring rate, as long as it ensures thorough mixing without splashing. In this invention, the particle size of the amorphous titanium precursor obtained by the hydrolysis method is preferably 1-20nm.

[0021] In this invention, the preferred method for preparing the titanium peroxide precursor gel is as follows: The raw material is added to deionized water, the pH is adjusted to 8-9, precipitation is carried out, followed by filtration and washing to obtain the precipitate. The precipitate is then mixed with hydrogen peroxide for oxidation treatment to obtain an amorphous titanium precursor. The raw material is one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid. The pH adjuster is preferably ammonia or sodium hydroxide. The concentration of ammonia is preferably 25-28 wt%. The precipitation temperature is preferably room temperature. The precipitation time is preferably 20-60 min, more preferably 30-40 min. The mass concentration of hydrogen peroxide is preferably 25-35%, more preferably 30%. The oxidation treatment time is preferably 0.5-2 h, more preferably 1-1.5 h. The oxidation treatment is preferably carried out under stirring conditions. This invention does not have a specific limitation on the amount of raw material and deionized water used; it can be determined based on the technical knowledge of those skilled in the art. This invention does not have a specific limitation on the specific operation of adding the raw material to deionized water; dripping or other methods are acceptable. This invention does not impose a specific limit on the stirring rate, as long as it ensures thorough mixing without splashing. This invention also does not impose specific limitations on the specific operations of filtration and washing, as long as impurities in the precipitate are removed. In this invention, the amorphous titanium precursor is preferably a titanium peroxide precursor gel.

[0022] In this invention, when the titanium source is anatase titanium dioxide and / or rutile titanium dioxide, it is preferable to use the titanium source directly or to grind and disperse it. This invention does not impose any particular limitations on the specific grinding and dispersion operations, as long as they achieve uniform dispersion.

[0023] This invention allows for the control of the microstructure of different titanium sources through appropriate processing, thereby flexibly regulating the particle size of the final barium titanate product. For example, using an amorphous titanium precursor obtained by hydrolysis, the particle size of the prepared tetragonal phase barium titanate nanoparticles can be controlled within the range of <100 nm; using an amorphous titanium precursor obtained by precipitation-oxidation, the particle size of the prepared tetragonal phase barium titanate nanoparticles can be controlled within the range of 100~200 nm.

[0024] In this invention, the barium source preferably includes one or more of the anhydrous and hydrated forms of barium carbonate, barium nitrate, barium hydroxide, barium oxalate, and barium peroxide.

[0025] In this invention, the molar ratio of TiO2 in the titanium source to BaO in the barium source is preferably 1:(1~1.3), more preferably 1:(1.1~1.2). The addition of an appropriate excess of barium in this invention helps to compensate for barium volatilization losses at high temperatures.

[0026] In this invention, the composite molten salt comprises a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride and / or barium fluoride; the auxiliary molten salt preferably comprises one or more of sodium chloride, potassium chloride, lithium chloride, and calcium chloride, more preferably a eutectic mixture of sodium chloride and potassium chloride; the molar ratio of sodium chloride to potassium chloride in the eutectic mixture is preferably 1:1; the mass ratio of the soluble barium salt to the auxiliary molten salt is preferably 1:(0.5~10); the mass ratio of the total mass of the titanium source and the barium source to the mass of the composite molten salt is preferably 1:(0.1~10). In embodiments of the present invention, the mass ratio of the soluble barium salt to the auxiliary molten salt can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10; the ratio of the total mass of the titanium source and the barium source to the mass of the composite molten salt can be 1:0.1, 1:0.2, 1:0.3, 1:0.5, 1:0.6, 1:0.8, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10. The present invention uses barium chloride and / or barium fluoride as key components of the composite molten salt. In the molten state, the soluble barium salt dissociates to generate a large amount of barium ions (Ba... 2+ This invention enables the formation of a barium ion-rich adsorption layer on the surface of barium titanate grains. This adsorption layer alters the interfacial energy and mass transfer kinetics of the grain surface, effectively inhibiting grain boundary migration and mass transport, thereby hindering grain coalescence and growth during calcination. Therefore, even when calcined over a wide temperature range of 650–1000 °C, the resulting tetragonal barium titanate powder maintains a nanoscale particle size. The auxiliary molten salt used in this invention has a low eutectic point, which is beneficial for forming a stable molten salt liquid phase.

[0027] In this invention, the inorganic base is sodium hydroxide and / or potassium hydroxide. Unlike Ba(OH)₂, sodium hydroxide or potassium hydroxide is introduced as an added inorganic base. NaOH and KOH not only do not decompose or become ineffective within the calcination temperature range, but also form a eutectic system with the molten salt, constructing a continuous, stable, and adjustable high-temperature alkaline molten salt environment. In this environment, OH… - It can act on the surface of titanium precursors, promoting the breaking and recombination of Ti-O bonds and inducing c-axis preferred distortion of titanium oxygen octahedrons ([TiO6]). This interfacial chemical reaction driven by an externally added alkali fundamentally lowers the thermodynamic energy barrier for the formation of the tetragonal phase, allowing the reaction to proceed efficiently at around 750℃ without relying on high-temperature thermal excitation.

[0028] In this invention, the preferred molar ratio of the inorganic base to the barium source is (0.05~2):1. In embodiments of this invention, the molar ratio of the inorganic base to the barium source can be 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.15:1, 0.18:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, or 2:1. This invention, by controlling the molar ratio of the inorganic base to the barium source, ensures a moderate alkaline environment, which can induce distortion while avoiding abnormal particle growth due to excessive alkali.

[0029] In this invention, the water is preferably deionized water. There is no particular limitation on the amount of water used; as long as it is sufficient to ensure uniform mixing of all components, it is acceptable.

[0030] In this invention, the preferred method for mixing the titanium source, barium source, composite molten salt, inorganic alkali, and water is to first mix the titanium source, barium source, composite molten salt, and inorganic alkali, and then add water and stir until homogeneous. This invention does not impose specific limitations on the stirring rate and stirring time; these can be determined based on the technical knowledge of those skilled in the art, as long as the components are mixed homogeneously.

[0031] This invention does not impose specific limitations on the drying parameters and operations; any method that ensures complete drying is sufficient, based on the technical knowledge of those skilled in the art. In embodiments of this invention, the drying method may be oven drying.

[0032] In this invention, the calcination temperature is preferably 650~1000℃; the calcination time is preferably 1~6h; and the heating rate to the calcination temperature is preferably 4~6℃ / min, more preferably 5℃ / min. In embodiments of this invention, the calcination temperature can be 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or 1000℃; and the calcination time can be 1h, 2h, 3h, 4h, 5h, or 6h. This invention achieves tetragonal phase transformation through calcination to obtain tetragonal barium titanate, while the relatively low calcination temperature significantly reduces energy consumption, demonstrating the energy-saving and consumption-reducing advantages of this invention.

[0033] After calcination, the present invention preferably further includes post-processing of the calcined product; the post-processing is preferably performed sequentially by cooling, washing, filtering and drying.

[0034] The present invention does not impose any special limitations on the specific operation of the cooling process; cooling can be performed along with the furnace.

[0035] In this invention, the detergent used for washing is preferably deionized water or a dilute acid solution; the temperature of the deionized water is preferably 80-100°C; the dilute acid solution is preferably a dilute nitric acid solution, dilute hydrochloric acid solution, or dilute sulfuric acid solution; the mass concentration of the dilute acid solution is preferably 0.01-1%. This invention does not have a specific limitation on the number of washes, which can be determined based on the technical knowledge of those skilled in the art, until no white precipitate is detected in the washing solution using silver nitrate solution. In embodiments of this invention, the number of washes can be 3-5 times. This invention can effectively remove residual molten salt through washing.

[0036] The present invention does not impose any special limitations on the specific operation of the filtration. Any conventional filtration method that can achieve solid-liquid separation is acceptable.

[0037] In this invention, the drying temperature is preferably 60~120℃; the drying time is preferably 6~24h. In embodiments of this invention, the drying temperature can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, or 120℃; the drying time can be 6h, 9h, 12h, 15h, 18h, 21h, or 24h. This invention removes residual moisture through drying.

[0038] The preparation method provided by this invention has the following advantages: (1) Significantly reduce the synthesis temperature of tetragonal barium titanate. This invention constructs a high-temperature stable alkaline molten salt field by adding an inorganic base (NaOH / KOH), which effectively reduces the formation energy barrier of tetragonal barium titanate, reducing the tetragonal phase transition temperature from 950℃ and higher required by conventional non-alkaline systems to 650~900℃, significantly reducing energy consumption and production costs.

[0039] (2) Wide temperature window with strong adaptability. The preparation method provided by the present invention can obtain tetragonal barium titanate products in a wide temperature range of 650~1000℃. The process window is wide and the operation is highly flexible, which is conducive to the control and stability of process parameters in industrial production.

[0040] (3) Effectively suppresses abnormal grain growth and achieves controllable nanoscale particle size. This invention uses barium chloride and / or barium fluoride as soluble barium salt flux components, and utilizes the adsorption effect of barium ions in the molten salt on the surface of barium titanate grains to effectively suppress grain boundary migration and mass transport, avoid abnormal grain growth and sintering during calcination, and ensure that the average particle size of the product is stably controlled within the range of 50~300nm.

[0041] (4) Flexible particle size control. By changing the preparation method and type of titanium precursor, the particle size of the final barium titanate powder can be flexibly controlled. For example, using an amorphous titanium precursor obtained by hydrolysis as a titanium source can yield tetragonal phase barium titanate nanoparticles with a particle size of less than 100 nm; using an amorphous titanium precursor obtained by precipitation-hydrogen peroxide method as a titanium source can yield tetragonal phase barium titanate nanoparticles with a particle size of 100~200 nm, meeting the differentiated particle size requirements of different application scenarios.

[0042] (5) The product has high tetragonality and high purity. The tetragonal phase barium titanate nanopowder prepared by the preparation method provided by the present invention has a pure tetragonal phase crystal structure, a c / a axis ratio ≥1.008, good crystallinity, and excellent dispersibility, which is beneficial to subsequent ceramic sintering and device preparation.

[0043] (6) The process is simple, the cost is low, and it is easy to industrialize. The present invention adopts the molten salt method combined with the aqueous phase mixing-drying process. The raw materials are widely available, the equipment requirements are low, the operation is simple, and there is no need for special equipment such as high-pressure reactors, making it easy to achieve large-scale production.

[0044] The preparation method provided by this invention can synthesize tetragonal barium titanate at relatively low temperatures (650~900℃), and tetragonal products can be obtained within a wide temperature window of 650~1000℃. Furthermore, the tetragonal phase content is >80%, and the powder exhibits high tetragonality, solving the problem of obtaining tetragonal phase in existing technologies. Through the rational design of the molten salt composition, this invention achieves stable control of the particle size of tetragonal barium titanate nanoparticles within the range of 50~300nm, with uniform particle size distribution, realizing controllable particle size preparation and solving the problem of abnormal growth of tetragonal phase grains in existing technologies. The preparation method provided by this invention is simple, low-cost, and easy for industrial production.

[0045] This invention provides tetragonal phase barium titanate nanopowder prepared by the preparation method described in the above technical solution.

[0046] In this invention, the tetragonal phase barium titanate nanoparticles preferably have a tetragonal crystal structure; the tetragonal phase content in the tetragonal phase barium titanate nanoparticles is preferably ≥80%; the c / a axis ratio of the tetragonal phase barium titanate nanoparticles is preferably ≥1.008; the average particle size of the tetragonal phase barium titanate nanoparticles is preferably 50~300 nm; the residual chlorine content of the tetragonal phase barium titanate nanoparticles is preferably less than 0.1 wt%; and the Ba to Ti molar ratio of the tetragonal phase barium titanate nanoparticles is preferably 0.99~1.05. The tetragonal phase barium titanate nanoparticles prepared by this invention have uniform particle size distribution, high crystallinity, and good dispersibility.

[0047] In this invention, the particle size of the tetragonal phase barium titanate nanoparticles is preferably ≤200 nm. In this invention, when the amorphous titanium precursor is obtained by hydrolysis, the particle size of the tetragonal phase barium titanate nanoparticles is preferably <100 nm; when the amorphous titanium precursor is obtained by precipitation-oxidation, the particle size of the tetragonal phase barium titanate nanoparticles is preferably 100~200 nm.

[0048] This invention also provides the application of the tetragonal phase nano-barium titanate powder described above in the field of electronic ceramics industry.

[0049] In this invention, the electronic ceramics industry field includes multilayer ceramic capacitors (MLCCs), ferroelectric non-volatile memories, and piezoelectric sensors.

[0050] The present invention does not impose any special limitation on the specific application method, and any application method known to those skilled in the art can be used.

[0051] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is dried in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 750 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium hydroxide octahydrate (Ba(OH)2·8H2O); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0053] The particle size distribution diagram of the amorphous titanium precursor in Example 1 is shown below. Figure 1 As shown. By Figure 1 It can be seen that the particle size of the amorphous titanium precursor prepared by hydrolysis using titanium tetrachloride as raw material in Example 1 is 1~20nm.

[0054] SEM image of the tetragonal phase barium titanate nanoparticles prepared in Example 1 is shown below. Figure 2 As shown; the XRD pattern of the tetragonal phase barium titanate nanopowder prepared in Example 1 is shown below. Figure 3 As shown. By Figure 2 and Figure 3 It can be seen that the XRD pattern shows that the main component of the tetragonal phase barium titanate nanopowder is tetragonal phase barium titanate. By calculating the area of ​​the (002) and (200) peaks, it is determined that the proportion of tetragonal phase barium titanate is >80%, and c / a >1.008. The SEM pattern shows that the particle shape of the tetragonal phase barium titanate nanopowder is nearly spherical or square, with no less than 200 particles and an average particle size of about 50~70nm.

[0055] Example 2 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is dried in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 750 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is titanium peroxide precursor gel; the preparation method of the titanium peroxide precursor gel is as follows: 10 mL of titanium tetrachloride is added dropwise to 20 mL of deionized water, and ammonia water with a concentration of 27 wt% is added under stirring conditions. After adjusting the pH value of the system to 9, the system is precipitated at room temperature for 30 min. Then, the precipitate is obtained by filtration and washing with deionized water three times. The precipitate is then mixed with 30 mL of hydrogen peroxide with a mass concentration of 30% and oxidized for 1 h to obtain titanium peroxide precursor gel. The barium source is barium hydroxide octahydrate (Ba(OH)2·8H2O); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.2:1.

[0056] SEM image of the tetragonal phase barium titanate nanopowder prepared in Example 2 is shown below. Figure 4 As shown; the XRD pattern of the tetragonal phase barium titanate nanopowder prepared in Example 2 is shown below. Figure 5 As shown. By Figure 4 and Figure 5 As can be seen from the XRD pattern, the main component of the tetragonal barium titanate nanoparticles is tetragonal barium titanate. Calculations show that the proportion of tetragonal barium titanate is 82%, and c / a>1.009. The SEM pattern shows that the shape of the tetragonal barium titanate nanoparticles is nearly spherical or square. According to statistics, the average particle size of the tetragonal barium titanate nanoparticles is about 110 nm.

[0057] Example 3 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source, a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 700 °C at a heating rate of 5 °C / min and calcined for 4 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is 8.0g of commercially available nano-anatase titanium dioxide (crystalline TiO2), which is ground and dispersed in an agate mortar. The barium source is barium nitrate (26.1 g, 0.1 mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2 g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8 g) and potassium chloride (7.5 g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.3:1.

[0058] SEM image of the tetragonal phase barium titanate nanoparticles prepared in Example 3 is shown below. Figure 6 As shown. By Figure 6 It can be seen that the tetragonal phase barium titanate nanoparticles are nearly spherical or square in shape; according to statistics, the average particle size of the tetragonal phase barium titanate nanoparticles is in the range of 150~200nm.

[0059] The main component of the tetragonal barium titanate nanopowder prepared in Example 3 is tetragonal barium titanate, with a proportion of >85% and c / a >1.01.

[0060] Example 4 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g as TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 700 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium oxalate (25.4 g, 0.1 mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium fluoride (10.0 g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8 g) and potassium chloride (7.5 g); the inorganic base is potassium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.2:1.

[0061] The tetragonal barium titanate nanoparticles prepared in Example 4 are mainly composed of tetragonal barium titanate, with a proportion of 85% and a c / a ratio > 1.009. The particle size of the tetragonal barium titanate nanoparticles is relatively uniform, with an average particle size of about 80-120 nm. This indicates that barium fluoride can also effectively inhibit grain growth and obtain small-particle-size tetragonal barium titanate nanoparticles.

[0062] Example 5 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g as TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 780 °C at a heating rate of 5 °C / min and calcined for 4 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0063] The tetragonal barium titanate nanoparticles prepared in Example 5 are mainly composed of tetragonal barium titanate, with a proportion >80% and a c / a ratio >1.008. Furthermore, the tetragonal barium titanate nanoparticles have a uniform particle size, with an average particle size of approximately 90-100 nm. This demonstrates that small-particle-size tetragonal barium titanate nanoparticles can also be obtained by using barium carbonate in combination with an added alkali.

[0064] Example 6 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source, a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 780 °C at a heating rate of 5 °C / min and calcined for 4 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is 8.0g of commercially available nano-rutile titanium dioxide (crystalline TiO2), which is ground and dispersed in an agate mortar; The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is potassium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.2:1.

[0065] The main component of the tetragonal barium titanate nanopowder prepared in Example 6 is tetragonal barium titanate, with a proportion of 80% and c / a > 1.008. At the same time, the tetragonal barium titanate nanopowder has a uniform particle size with an average particle size of about 120 nm.

[0066] Example 7 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g as TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 700 °C at a heating rate of 5 °C / min and calcined for 2 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium peroxide (16.9 g, 0.1 mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (8.0 g) and barium fluoride (4.0 g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8 g) and potassium chloride (7.5 g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0067] The tetragonal barium titanate nanoparticles prepared in Example 7 are mainly composed of tetragonal barium titanate, with a proportion of 80% and a c / a ratio > 1.008. Furthermore, the tetragonal barium titanate nanoparticles exhibit uniform particle size, with an average particle size of approximately 80 nm. Compared to using barium chloride alone, the composite barium salt system can achieve fine particle sizes with a short holding time.

[0068] Example 8 A method for preparing tetragonal phase barium titanate nanopowder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is dried in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 950 °C at a heating rate of 5 °C / min and calcined for 2 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain tetragonal phase barium titanate nanopowder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium hydroxide octahydrate (Ba(OH)2·8H2O); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0069] The tetragonal barium titanate nanoparticles prepared in Example 8 are highly crystalline tetragonal barium titanate with an average particle size of approximately 180 nm, still within the 50-300 nm range. This indicates that the soluble barium salt flux used in this invention remains effective in inhibiting grain growth at high temperatures.

[0070] Comparative Example 1 A method for preparing nano-barium titanate powder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, and a composite molten salt are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is dried in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 750 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g).

[0071] SEM image of the barium titanate nanoparticles prepared in Comparative Example 1 is shown below. Figure 7 As shown; the XRD pattern of the barium titanate nanoparticles prepared in Comparative Example 1 is shown below. Figure 8 As shown. By Figure 7 and Figure 8 SEM observation shows that the tetragonal barium titanate nanoparticles have a uniform particle size distribution, with dimensions within 100 nm; however, XRD analysis reveals that the main component of the barium titanate nanoparticles is cubic barium titanate, accompanied by unreacted BaCO3 impurity peaks. This indicates that omitting the addition of inorganic base results in a lack of external OH-. - In an alkaline environment, the system cannot break through the thermodynamic energy barrier for tetragonal phase formation at 750℃, proving that an external alkaline environment is the key factor for achieving low-temperature tetragonal phase transformation.

[0072] Comparative Example 2 A method for preparing nano-barium titanate powder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, an auxiliary molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the mixture is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 750 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the auxiliary molten salt is a eutectic mixture of sodium chloride (11.8g) and potassium chloride (13.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0073] The main component of the barium titanate nanoparticles prepared in Comparative Example 2 was tetragonal barium titanate, with a tetragonal phase content >80%; however, the grains of the barium titanate nanoparticles underwent severe abnormal growth, with an average particle size exceeding 600 nm. This indicates that when the addition of soluble barium salt is omitted: although the added alkaline environment promotes the tetragonal phase transformation, the lack of Ba provided by the soluble barium salt results in insufficient Ba production. 2+ The adsorption layer cannot suppress grain boundary migration, leading to uncontrolled grain growth. This demonstrates that soluble barium salts are the core mechanism for achieving nanoscale particle size control.

[0074] Comparative Example 3 A method for preparing nano-barium titanate powder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, and an auxiliary molten salt are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the slurry is dried in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 900 °C at a heating rate of 5 °C / min and calcined for 3 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the auxiliary molten salt is a eutectic mixture of sodium chloride (11.8g) and potassium chloride (13.5g).

[0075] SEM image of the barium titanate nanoparticles prepared in Comparative Example 3 is shown below. Figure 9 As shown, although the barium titanate nanoparticles prepared in Comparative Example 3 had transformed into the tetragonal phase, their particle size was uneven, and some particles had a diameter exceeding 500 nm. This demonstrates that by omitting the addition of inorganic alkali, traditional non-alkaline systems, even at a higher calcination temperature of 900°C for the same duration, cannot obtain high-purity and fine-particle-size tetragonal barium titanate nanoparticles at 750°C as in this invention, highlighting the advantages of this invention in terms of low temperature and high efficiency.

[0076] Comparative Example 4 A method for preparing nano-barium titanate powder is as follows: a titanium source (0.1 mol, 8.0 g as TiO2), a barium source, and an inorganic base are placed in an agate mortar, with only a small amount of ethanol added to aid grinding. Solid-phase mixing is carried out to obtain a mixture. The mixture is then transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 750°C at a heating rate of 5°C / min and calcined for 3 hours. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80°C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100°C for 12 hours to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7 g, 0.1 mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0077] SEM image of the barium titanate nanoparticles prepared in Comparative Example 4 is shown below. Figure 10As shown, unreacted raw materials are present in the nano-barium titanate powder, and the barium titanate conversion rate is less than 80%. Furthermore, the nano-barium titanate powder has an uneven particle size and a relatively large particle size. This indicates that the lack of a molten salt liquid phase medium means the reactants rely solely on solid-solid diffusion, resulting in incomplete reaction and a significant increase in particle size. This demonstrates that a molten salt environment is a fundamental condition for achieving a complete reaction at low temperatures.

[0078] Comparative Example 5 A method for preparing nano-barium titanate powder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the mixture is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 780 °C at a heating rate of 5 °C / min and calcined for 4 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium carbonate, and the molar ratio of the inorganic base to the barium source is 0.1:1.

[0079] The main component of the barium titanate nanoparticles prepared in Comparative Example 5 was cubic barium titanate, with a c / a axial ratio close to 1.000 and a particle size greater than 300 nm. Note: Only alkali metal ions were present, without OH-. - In a strongly alkaline environment, the distortion of the titanium-oxygen octahedron cannot be effectively induced, making it difficult to obtain the tetragonal phase. This further illustrates that the "inorganic base" in this invention specifically refers to the base that can provide OH-. - Hydroxides.

[0080] Comparative Example 6 A method for preparing nano-barium titanate powder is as follows: First, a titanium source (0.1 mol, 8.0 g of TiO2), a barium source, a composite molten salt, and an inorganic alkali are mixed. Then, 50 mL of deionized water is added and stirred for 30 min to form a uniform slurry. Next, the mixture is placed in an oven at 110 °C for 12 h to obtain a mixture. Then, the mixture is transferred to a corrosion-resistant crucible and placed in a muffle furnace. The temperature is increased to 780 °C at a heating rate of 5 °C / min and calcined for 4 h. After calcination, the mixture is cooled to room temperature and then washed 5 times with deionized water at 80 °C until no white precipitate is detected by silver nitrate solution. After filtration, the mixture is dried in an oven at 100 °C for 12 h to obtain nano-barium titanate powder. The titanium source is an amorphous titanium precursor; the preparation method of the amorphous titanium precursor is as follows: 10 mL of titanium tetrachloride is added dropwise to 100 mL of deionized water, and then hydrolyzed for 5 h under stirring and temperature of 90 °C. After filtration, the amorphous titanium precursor is obtained. The barium source is barium carbonate (19.7g, 0.1mol); the molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:1.1; the composite molten salt is a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride dihydrate (12.2g); the auxiliary molten salt is a eutectic mixture of sodium chloride (5.8g) and potassium chloride (7.5g); the inorganic base is sodium hydroxide, and the molar ratio of the inorganic base to the barium source is 5:1.

[0081] The main component of the nano-barium titanate powder prepared in Comparative Example 6 was tetragonal barium titanate, but the average particle size exceeded 500 nm and the morphology was irregular. This indicates that excessive inorganic alkali will lead to excessively high alkalinity in the molten salt system and excessively rapid ion diffusion, which in turn leads to abnormal grain growth. This shows that controlling the amount of inorganic alkali is crucial.

[0082] Table 1 shows a comparison between the tetragonal barium titanate nanopowders prepared in Examples 1, 3, and 5 and the barium titanate nanopowders prepared in Comparative Examples 1-3 and Comparative Examples 5-6. Table 1. Comparison results of tetragonal barium titanate nanopowder prepared in Examples 1, 3, and 5 with barium titanate nanopowder prepared in Comparative Examples 1-3 and Comparative Examples 5-6.

[0083] As can be seen from Table 1, the present invention effectively induces titanium oxide octahedral distortion by adding an inorganic base to provide an alkaline environment, thereby obtaining a tetragonal phase. The addition of soluble Ba salt controls the grain size and phase transformation temperature, thus achieving the low-temperature preparation of tetragonal phase nano-barium titanate.

[0084] In summary, the method for preparing tetragonal phase nano-barium titanate provided by this invention requires a low calcination temperature, has a stable process, is easy to operate, and is inexpensive. The resulting barium titanate powder has the characteristics of controllable particle size, high purity, and high tetragonal phase content, making it suitable for large-scale industrial production in fields such as multilayer ceramic capacitors, dielectric materials, and piezoelectric materials.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing tetragonal phase barium titanate nanoparticles, comprising: Titanium source, barium source, composite molten salt, inorganic alkali and water are mixed and dried to obtain a mixture. The mixture is then calcined to obtain tetragonal phase barium titanate nanopowder. The titanium source is one or more of amorphous titanium precursor, peroxide titanium precursor gel, anatase titanium dioxide, and rutile titanium dioxide; the amorphous titanium precursor is obtained by hydrolysis of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid; the peroxide titanium precursor gel is obtained by precipitation-oxidation of one or more of titanium tetrachloride, tetrabutyl titanate, titanium oxysulfate, and metatitanic acid. The composite molten salt comprises a soluble barium salt and an auxiliary molten salt; the soluble barium salt is barium chloride and / or barium fluoride; The inorganic base is sodium hydroxide and / or potassium hydroxide.

2. The preparation method according to claim 1, characterized in that, The barium source includes one or more of the anhydrous and hydrated forms of barium carbonate, barium nitrate, barium hydroxide, barium oxalate, and barium peroxide.

3. The preparation method according to claim 1, characterized in that, The molar ratio of TiO2 in the titanium source to BaO in the barium source is 1:(1~1.3).

4. The preparation method according to claim 1, characterized in that, The auxiliary molten salt includes one or more of sodium chloride, potassium chloride, lithium chloride, and calcium chloride.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the soluble barium salt to the auxiliary molten salt is 1:(0.5~10).

6. The preparation method according to claim 1, characterized in that, The ratio of the total mass of the titanium source and the barium source to the mass of the composite molten salt is 1:(0.1~10).

7. The preparation method according to claim 1, characterized in that, The molar ratio of the inorganic base to the barium source is (0.05~2):

1.

8. The preparation method according to claim 1, characterized in that, The calcination temperature is 650~1000℃, the calcination time is 1~6h, and the heating rate to the calcination temperature is 4~6℃ / min.

9. Tetragonal phase barium titanate nanopowder prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the tetragonal phase barium titanate nanopowder according to claim 9 in the field of electronic ceramics industry.

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