钛酸锶钡压电陶瓷超细粉体的水热法合成

采用水热工艺制备不同组成的BaxSr1-xTiO3(BST)，利用FT-IR，XRD，TEM等技术分析了水热反应转变机理及相结构转变情况，同时对影响合成的工艺参数以及不同组成材料的居里温度变化进行了研究。结果表明：获得的BST粉体颗粒粒度较细，粒径为20～40nm。其最佳的工艺参数为n(Ba)／n(Ti)=3，n(Sr)／n(Ti)=1／4或者n(Ba)／n(Ti)=1／3，n(Sr)／n(Ti)=4／5，cKOH=1．5～2mol／L。制得不同组成粉体的居里温度呈规律性变化。     

Synthesis of barium strontium titanate nanopowders by microwave hydrothermal method

Barium strontium titanate (BST) powders of high purity, good crystallinity and well dispersed with a diameter of 50–90?nm are prepared by microwave hydrothermal method using tetrabutyl titanate, barium nitrate and strontium nitrate as the main raw materials. The phase composition, element composition and microstructure of the powders are characterised by X-ray diffraction, Fourier transform infrared spectroscopy, energy dispersive spectroscopy and transmission electron microscopy. The results show that Ba_0.6Sr_0.4TiO₃ powders could be synthesised under the conditions that the reaction temperature is 70°C, the reaction time is 10?min, and the value of pH is 14, which indicates that the reaction temperature, time and the value of pH have a great effect on the crystallinity of nanopowders, and the dispersant (OP-10) plays a role in the dispersion of the nanopowders.     

Effects of phase constitution and microstructure on energy storage properties of barium strontium titanate ceramics

Barium strontium titanate (Ba_0.3Sr_0.7TiO₃, BST) ceramics have been prepared by conventional sintering (CS) and spark plasma sintering (SPS). The effects of phase constitution and microstructure on dielectric properties, electrical breakdown process and energy storage properties of the BST ceramics were investigated. The X-ray diffraction analysis and dielectric properties measurements showed that the cubic and tetragonal phase coexisted in the SPS sample while the CS sample contained only tetragonal phase. Much smaller grain size, lower porosity, fewer defects and dislocation were observed in SPS samples, which greatly improved the electrical breakdown strength of the Ba_0.3Sr_0.7TiO₃ ceramics. The enhanced breakdown strength of the SPS samples resulted in an improved maximum electrical energy storage density of 1.13 J/cm³ which was twice as large as that of the CS sample (0.57 J/cm³). Meanwhile, the energy storage efficiency was improved from 69.3% to 86.8% by using spark plasma sintering.     

Effects of cerium doping on dielectric properties and defect mechanism of barium strontium titanate glass-ceramics

The effect of cerium content on phase evolution, dielectric properties and defect mechanism has been investigated in (Ba,Sr)TiO₃ glass-ceramics. Cerium mainly acts as an isovalent dopant in the B-site of ABO₃ perovskite structure at low content (1 mol%) and then cerium substitution gradually occurs in the A-site with increasing cerium content. A compensation mechanism related to variation in oxygen vacancy concentration has been identified. When cerium content increased to 2 mol%, the maximum values of dielectric constant and energy storage density were simultaneously achieved. The impedance spectra revealed the highest conductivity. It is due to the increase in the concentration of charge carriers accompanied by the decrease in the activation energy of oxygen vacancy migration. With a further addition of cerium to 3 mol%, the opposite trend was observed. The result is related to the presence of more cation vacancies, which, in turn, limits the diffusion rate of oxygen vacancy.     

Fabrication of highly dispersed crystallized nanoparticles of barium strontium titanate in the presence of N,N-dimethylacetamide

Highly dispersed nanoparticles of barium strontium titanate (BST) were successfully synthesized by hydrolysis method using N,N-dimethylacetamide as a solvent at 120 °C and 140 °C. X-ray diffraction analysis (XRD) showed that the as-prepared particles presented a perovskite polycrystalline structure. The result of transmission electron microscopy (TEM) images revealed the particle size in the range of 5-30 nm. The composition without any annealing treatment characterized with the parallel plate capacitor method displayed good dielectric properties.     

Effect of strontium doping on structural and dielectric behaviour of barium titanate nanoceramics

ABSTRACT

Barium strontium titanate (Ba_(1?x)Sr_xTiO₃ where, x?=?0.0, 0.2, 0.3, 0.4 and 0.5) nanoparticles have been successfully synthesised by sol–gel method and characterised thoroughly. With the increase in Sr concentration (x?>?0.3), the symmetry of the crystal structure changed from tetragonal to cubic phase. The dielectric behaviour of the ceramic nanoparticles was evaluated using impedance analyser with an operating frequency of 1?Hz to 1?MHz. A very high dielectric constant 4915 was obtained for Ba_0.7Sr_0.3TiO₃ at 1?Hz frequency with low dielectric loss of 1.91, which showed very good value than the one previously reported. The density of the material was found to be >98% of theoretical density. Dielectric constants were measured by varying the temperature from 35 to 150°C and the Curie temperatures were also evaluated. The small amount of Sr doping was beneficial for obtaining high dielectric constant material which can be used in various electronic applications.     

Composition and annealing effects on the linear electro-optic response of solution-deposited barium strontium titanate

Chemical solution deposition was used to deposit epitaxial Ba_xSr_(1−x)TiO₃ thin films on SrTiO₃ template layers on Si(001) for x = 1.0, 0.7, 0.5, 0.3, and 0.0. Effective Pockels coefficients were determined as a function of film composition both for as-deposited films (crystallized at 600°C) and for the films after annealing at 750°C for 10 hours. Pockels response decreased monotonically with decreasing Ba content and coefficients were higher for annealed films, reaching 89 ± 3 pm/V for annealed BaTiO₃. These results are contextualized with the aid of X-ray diffraction and high-resolution transmission microscopy, which illuminated the crystallinity and defect nature of the films.     

Direct and indirect measurement of large electrocaloric effect in barium strontium titanate ceramics

Barium strontium titanate (Ba_1-xSr_xTiO₃-BST) ceramics, where x = 0.05, 0.15, 0.25, and 0.35, was prepared via a solid-state reaction method. The lattice structures and morphologies of the ceramic samples were analyzed using X-ray diffraction and scanning electron microscopy technologies. The dielectric and ferroelectric properties of the BST ceramics were characterized using a precision impedance analyzer and a ferroelectric polarization-electric field (P-E) hysteresis loop tester, respectively. The electrocaloric effect was indirectly calculated using the Maxwell relations and P-E loops as a function of temperature and electrical field, and also directly measured using a computer-controlled thermocouple and high-voltage power supply. An adiabatic temperature change of 1.82 K was procured, indicating a promising potential in the applications as cooling devices.     

钛酸锶粉体合成新方法研究

以四氯化钛和氯化锶为原料，碳酸铵和氨水作沉淀剂化学共沉淀法合成钛酸锶粉体，研究了工艺条件对产品纯度和锶钛比的影响，最佳反应条件为：氯化锶与四氯化钛摩尔比为1．02，碳酸铵与氯化锶摩尔比为1．40，反应温度为室温，反应时间4h,pH=10，煅烧温度900℃，煅烧时间4h，所得产品经化学，红外光谱，电镜，X－射线衍射和原子发射光谱分析，分析结果显示：产品纯度高，粒径小，锶钛化合适。     

Preparation and characterisation of BaTiO3 nanopowder by microwave assisted microemulsion method

Through the microwave assisted reverse microemulsion method, BaTiO₃ nanopowders are prepared in 10 min by selecting water/OP-10/hexanol/cyclohexane reverse microemulsion system, Ba(NO₃)₂ and tetrabutyl titanate as reactants. The effect of reaction temperature, reaction time, concentration of reactants and molar ratio of water and surfactant on the reaction was studied, and the prepared powders were characterised by X-ray diffraction, TEM and X-ray fluorescence analysis. The results show that cubic phase BaTiO₃ powders of particle size about 50–80 nm with uniform distribution and good dispersion were prepared under atmospheric pressure in 10 min at 65°C. The method has characteristics of lower reaction temperature, shorter reaction time, smaller particle size, narrow particle size distribution and good particle dispersion.     

Evolved gas analysis during sintering of barium titanate

The gases evolved during the sintering of BaTiO₃ have been examined with a combined dilatometer and mass spectrometer (CDMS) apparatus. The CDMS acquires multiple mass/charge ratios in real time while simultaneously recording dilatometry data. To identify the chemical composition of the numerous recorded mass/charge ratios, cracking patterns, isotopic abundances and decomposition reactions from model compounds (BaCO₃, BaSO₄) were used. Three primary regions of gas evolution were identified. During the heating ramp and into the hold period at 1350°C, CO₂ appears, and below approximately 500°C, this may arise from adsorbed or surface CO₂. Sulphur dioxide was also observed, and its evolution occurred directly after the majority of the CO₂ appeared and immediately preceded the onset of sintering. Above 1200°C, CO₂ is the primary species observed in the gas phase. The implications of the high temperature chemistry on sintering and on microstructural development are discussed.     

纳米钛酸锶粉体制备及其表面改性工艺研究

钛酸锶（SrTiO3）是制备陶瓷电容器和热敏电阻器等电子陶瓷的重要原料,在电子工业上的应用非常广泛。以四氯化钛和氯化锶、氢氧化钠为原料,采用直接沉淀法合成纳米钛酸锶粉体,重点研究了表面活性剂十二烷基苯磺酸钠（SDBS）在合成过程中对纳米钛酸锶粉体性能的影响,并应用XRD,TEM,SEM,BET等一系列手段对其微观结构进行表征。结果表明表面活性剂SDBS的添加浓度有一最佳值（0.15 mol/L）。通过SDBS改性后的纳米钛酸锶粉体,其晶型结构没有发生改变,颗粒的形状为球形,平均粒径约为25 nm,粒度分布较窄,团聚现象也大为改善。     

Optical properties of multi-stacked BaTiO3/SrTiO3 thin films synthesized via chemical method

In this work, the BaTiO₃ and SrTiO₃ thin films as well as BaTiO₃/SrTiO₃ lamellar composites are synthesized via sol-gel spin-coating method. The formation of corresponding phases from their sols is investigated by virtue of X-ray diffraction on their powders, which confirms the formation of tetragonal structure for BaTiO₃, but cubic structure for SrTiO₃. The field emission scanning electron microscopy images show that crack-free films with different morphologies are formed in each sample. Likewise, by changing periodicity of the samples, the morphology of the composite samples is changed. As the number of layers increases from 1 to 20, the band gap reduces from 4.38 eV to 4.10 eV for BaTiO₃ samples and from 4.13 eV to 3.80 eV for SrTiO₃ samples confirmed by UV–Vis spectra. The band gap of periodicity = 1 sample is higher than that of BaTiO₃, while band gaps of periodicity = 2 and 5 composites mount between those of BaTiO₃ and SrTiO₃. In addition, the refractive indices of multi-stacked composites are about 0.2 lesser than refractive indices of BaTiO₃ sample in high wavelengths. The periodicity dependence of optical frequency dielectric constant, dielectric loss, impedance, Urbach tail, extinction coefficient, and electric modulus of multi-stacked composites are also studied.     

Nanostructured barium titanate ceramics

Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO₃) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 °C of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing.Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.     

High pressure FAST of nanocrystalline barium titanate

This work studies the microstructural evolution of nanocrystalline (<1 µm) barium titanate (BaTiO₃), and presents high pressure in field-assisted sintering (FAST) as a robust methodology to obtain >100 nm BaTiO₃ compacts. Using FAST, two commercial ~50 nm powders were consolidated into compacts of varying densities and grain sizes. Microstructural inhomogeneities were investigated for each case, and an interpretation is developed using a modified Monte Carlo Potts (MCP) simulation. Two recurrent microstructural inhomogeneities are highlighted, heterogeneous grain growth and low-density regions, both ubiqutously present in all samples to varying degrees. In the worst cases, HGG presents an area coverage of 52%. Because HGG is sporadic but homogenous throughout a sample, the catalyst (e.g., the local segregation of species) must be, correspondingly, distributed in a homogenous manner. MCP demonstrates that in such a case, a large distance between nucleating abnormal grains is required—otherwise abnormal grains prematurely impinge on each other, and their size is not distinguishable from that of normal grains. Compacts sintered with a pressure of 300 MPa and temperatures of 900 °C, were 99.5% dense and had a grain size of 90±24 nm. These are unprecedented results for commercial BaTiO₃ powders or any starting powder of 50 nm particle size—other authors have used 16 nm lab-produced powder to obtain similar results.     

3D-printed barium strontium titanate-based piezoelectric scaffolds for bone tissue engineering

In order to promote bone healing, new generations of biomaterials are under development. These biomaterials should demonstrate proper biological and mechanical properties preferably similar to the natural bone tissue. In this research, 3D-printed barium strontium titanate (BST)/β-tricalcium phosphate (β-TCP) composite scaffolds have been synthesized as an alternative strategy for bone regeneration to not only induce appropriate bioactive characteristics but also piezoelectric behavior. The physical, chemical and biological performance of the scaffolds have been examined in terms of mechanical, dielectric properties, apatite-forming ability, Alizarin Red Staining (ARS), Alkaline Phosphatase activity (ALP), and cytotoxicity. The samples composed of 60% BST and 40% β-TCP showed the highest compressive strength, bending module, elastic modulus and the Young's modulus. The dielectric constant increased with further addition of the BST phase in the constructs. Scanning Electron Microscope (SEM) and energy dispersive X-ray (EDX) analyses showed that 60% BST/40% β-TCP sample had the highest amount of bone-like apatite formation after 28 days in simulated body fluid (SBF). Moreover, the results of ARS proved that 60% BST/40% β-TCP composite could present higher quantities of mineral deposition. The ALP activity of osteosarcoma cells on 60% BST/40% β-TCP sample showed higher activities compare with the other composites. None of the samples demonstrated any sign of toxicity using MTT test. It can be suggested that BST/β-TCP composite scaffolds can be potentially used as the next generation of bone tissue engineering scaffold materials.     

锆钛酸锶的烧结及其介电性能表征

以四氯化钛、氧氯化锆、硝酸锶和氢氧化钠为原料,采用共沉淀法在25℃反应90℃陈化2h制备了锆钛酸锶(SrTixZr1-xO3)粉体,用X射线衍射(XRD)表征了锆钛酸锶粉体的物相.用透射电子显微镜表征了锆钛酸锶粉体的粒径.并采用干压成型法压制素坯进行烧结;确定了烧结制度为:升温速率3℃/min,1 400℃保温4h.对烧结后的陶瓷坯体进行介电性能表征,在1 kHz下SrTio.7 Zr0 3 O3陶瓷坯体的相对介电常数为135.6,介电损耗tanδ为24.4×10-3;SrTi0 5 Zro.5 O3陶瓷坯体的相对介电常数为122.3,介电损耗tanδ为137.38×10-3.     

钛酸锶生产工艺的现状与发展

论述了电子陶瓷材料钛酸锶生产工艺的现状与发展,讨论了各种方法的优缺点。     

Modification of barium titanate sintering via rare earth oxides addition: Dilatometric and microstructural study

In this paper, the effect of rare-earth dopants (RE: Ce, Eu, Tb, Dy, and Er) in barium titanate (BT) on the shaping, sintering and microstructure was studied aimed mainly at selecting appropriate dopant for densification delaying while preserving optimal BT characteristics. The addition of dopant oxides into suspension resulted in the reduction of the deposition kinetics. The relative density of doped green bodies was lower than pure BT and decreased with dopant concentration. Only Ce enhanced green density up to 2%. The sintering process was studied using high-temperature dilatometry. The hindering densification caused by dopants was observed, but only 5 wt % of Tb and Er in BT shifted the onset of sintering to higher temperatures that has the potential applicability of these materials in layered ceramic harvesters. The significant positive impact of doping on the microstructure was attained almost in all cases manifesting themselves in higher sintered densities and markedly lower mean grain size compared to pure BT. The XRD and Raman spectroscopy analyses confirmed incorporation of the dopants into the perovskite structure and no significant existence of RE-enriched secondary phases in the microstructure.     

The effect of pH control on synthesis of Sr doped barium titanate nanopowder by oxalate precipitation method

Sr substituted BaTiO₃ (BST) nanopowders were prepared using oxalate co-precipitation methods. During synthesis, oxygen was applied to the oxalate solution in order to control the oxidation states of Ti. Control of pH in the solution results in different crystalline phases of the powders after calcination; pure perovskite BST was obtained in the powder prepared at pH 3 solution, while perovskite BaTiO₃ (BTO) and impurities were observed in powders prepared at pH 1 solution. Phase transformation from amorphous to crystalline BST during heat treatment was discussed by different analysis technique. Also, morphology and elemental distribution of the pure BST was investigated.