The crystal structures and dielectric properties of Bi2O3 doped SrBi2Ta2O9 ceramics

Ferroelectric materials with Bi-layered structure such as SrBi₂Ta₂O₉ composition with excess x wt.% Bi₂O₃ (x = 0, 2, and 4) are investigated as the main composition, the effect of excess Bi₂O₃ content and sintering temperatures on the crystal structure and dielectric characteristics of SrBi₂Ta₂O₉ ceramics are developed. Even 1280 °C is used as the sintering temperature of stoichiometry SrBi₂Ta₂O₉ composition, the X-ray diffraction patterns will show that the SrBi₂Ta₂O₉ phase is coexisted with the raw material of Ta₂O₅ and the secondary phases of SrBi₂O₄ and BiTaO₄. For SrBi₂Ta₂O₉ composition with excess 2 wt.%- or 4 wt.%-Bi₂O₃-doped and sintered at 1040 °C, the Ta₂O₅, SrBi₂O₄, and BiTaO₄ phases are eliminated and only the SrBi₂Ta₂O₉ phase is observed in the X-ray diffraction patterns. It is found that sintering temperatures and excess Bi₂O₃ content have large influence on the grain growth, the bulk densities, the maximum dielectric constants, and the Curie temperatures of SrBi₂Ta₂O₉-based ceramics.     

Preparation and electrical properties of SrBi2Ta2O9 ceramic

SrBi₂Ta₂O₉ (SBT) ceramic materials were prepared by the conventional mixed-oxide method. Ceramics sintered at different temperatures had distinctly different microstructures. Anisometric plate-like crystalline grains were observed which revealed the layered structure of the material. The variations of the saturation polarization (P_s), remanent polarization (P_r) and coercive field (E_c) with applied field and temperature were studied by hysteresis (P-E) loop measurements. Samples were also DC poled at various temperatures and electric fields, and their permittivity, piezoelectric (d₃₃) and pyroelectric coefficient (p) were measured.     

Crystal structure and dielectric properties of La3+ substituted Ba5LaTi3Ta7O30 ceramics

The effects of La³⁺ partial substitution for Ba²⁺ on crystal structure and dielectric properties were investigated for modification of Ba₅LaTi₃Ta₇O₃₀ ceramics. When the substitution x > 0.6, the sintering temperature obviously decreased. Superstructure peaks were observed for more La³⁺ substitution (x ≥ 2.4). The stability of the tetragonal tungsten bronze phase was discussed with electronegativity difference and tolerance factor. Lattice parameters decreased at first, and then slightly increased; while axial ratio decreased with increasing La content. Dielectric constant slightly increased when x < 1.2, then gradually declined with the increase of La substitutions for Ba. Dielectric loss was very low except x = 2.4. Temperature coefficient of dielectric constant (at 1 MHz) was remarkably improved. The variation of dielectric properties was discussed from the change of crystal structure as well as the effects of vacancies at A-sites and superstructure.     

SrBi2Ta2O9铁电薄膜的三阶非线性光学性能的研究

采用射频磁控溅射法在石英玻璃衬底上制备出均匀透明的SrBi2Ta2O9(SBT)薄膜,根据透射谱计算表明薄膜样品厚度为349nm,线性折射率为3.05.以锁模Nd:YAG激光器作为光源,利用Z-scan技术测定了薄膜的非线性光学性能.结果表明薄膜的非线性折射率n2＝2.56×10-8esu,非线性光吸收系数β＝3.93×10-4 esu,其三阶非线性极化率的实部和虚部分别为:Reχ(3)＝8.29×10-9 esu和Imχ(3)＝1.08×10-9 esu.     

Dielectric properties of La2O3-doped Ba0.8Sr0.2TiO3 ceramics

La₂O₃-doped Ba_0.8Sr_0.2TiO₃ dielectric ceramics were prepared by conventional solid state ceramic route. Scanning electron microscope was employed to observe the surface morphologies. The capacitance C and dielectric loss factor D of the samples were measured with automatic LCR Meter 4225 at 10 kHz respectively. The results show that: ε _r of the samples decreases and tgδ first decreases then increases with increasing amount of La₂O₃ doping. ε _r reaches better value, tgδ obtains the minimum value at 0.5 mol% La₂O₃. ε _r increases and tgδ decreases when sintering temperature increases. The samples doped with 0.5 mol% La₂O₃ sintered at 1,350 °C for 10 h exhibited attractive properties, including high relative dielectric constant (>4,000), low dielectric loss (16.8 × 10^?4), low temperature coefficient of relative dielectric constant(<±21 %) in the temperature range of +25 to +85 °C.     

X-ray photoelectron spectroscopy and electrical properties studies of La2O3-doped strontium titanate ceramics prepared by sol-precipitation method

X-ray photoelectron spectroscopy has been used to investigate the existence of Ti³⁺ on the surface of La₂O₃-doped strontium titanate and to determine its surface characteristics. The surfaces, having Sr/Ti ratios significantly varying from the stoichiometric ratio, revealed the presence of carbon and suggested the presence of hydroxyl groups on the surface, whose concentration largely decreased in the bulk. Ti³⁺ species existed as a function of the sintering conditions and were detected on the surface of (La, Sr)TiO₃ sintered in air or in N₂ by natural cooling. These samples had a lower electrical resistivity, especially when sintered in a N₂ atmosphere. The surfaces of air oxidized SrTiO₃ and quenched from high temperature contained no detectable amount of Ti³⁺, resulting in higher resistivity. However, the N₂-sintered samples were dark blue in color and exhibited lower resistivity, semiconductivity, and lower valence oxidation state Ti existed when sintered above 1350°C.     

Effect of Co3+ on structure and electrical properties of Na0.5Bi2.5Nb2O9 ceramics

Journal of Materials Science: Materials in Electronics - Na0.5Bi2.5Nb2-xCoxO9 (NBNC-x, x?=?0.00, 0.02, 0.05, 0.07, 0.09) bismuth layered piezoelectric ceramics were synthesized by the...     

Effect of La/Sn co-substitution for Ba/Ta on crystal structure and dielectric properties of Ba5NdTi3Ta7O30 ceramics

The effects of La/Sn co-substitution for Ba/Ta were investigated for the modification of Ba₅NdTi₃Ta₇O₃₀ ceramics. The modified ceramics (Ba_5?x La _x )NdTi₃(Ta_7?x Sn _x )O₃₀ exhibited single tetragonal tungsten bronze phase for x<1.5, while a small amount of secondary phase BaTi₄O₉ was observed for x>1.5. The lattice constants decreased with increasing La/Sn content, while the axial ratio 10^1/2c/a decreased when x was below 1.5, then slightly increased. With increasing La and Sn content, the temperature coefficient of dielectric constant (at 1 MHz) was remarkably lowered from ?1560 ppm/ °C to ?286 ppm/ °C, while the dielectric constant gradually reduced, and the dielectric loss slightly increased. There were some clear relationships between the temperature coefficient and bond valence, tolerance factor: the temperature coefficient of dielectric constant linearly increased when the bond valence of the ions at B sites increased, while the same effect occurred when the tolerance factor decreased. In addition, the stability of the tetragonal tungsten bronze phase is discussed in relation to electronic difference and tolerance factor.     

Electrical characteristics of the MOD-derived SrBi2xTa2O9 and SrBi2.4(Ta,Nb)2O9 thin films

Ferroelectric and leakage current characteristics of the MOD-derived SrBi_2xTa₂O₉ (0.8 x 1.6) and SrBi_2.4(Ta_1-yNb_y)₂ O₉ (0 y 1) thin films were investigated. The SBT and SBTN films were fully crystallized to Bi-layered perovskite structure by annealing at 800°C for 1 hour in oxygen atmosphere. The ferroelectric characteristics of the SBT films were optimized at the Bi/Ta mole ratio x of 1.2. The leakage current density of the Bi-excess SBT films decreased remarkably by the post-metallization annealing at 800°C for 10 minutes in oxygen ambient. The ferroelectric characteristics of the SBTN films were optimized with the SBN content y of 0.25. The SrBi_2.4(Ta_0.75Nb_0.25)₂ O₉ film exhibited 2P_r and E_c of 19.04 C/cm² and 24.94 kV/cm at ±5 V, which were superior to 2P_r of 11.3 C/cm² and E_c of 39.6 kV/cm obtained for the SrBi_2.4Ta₂O₉ film after the post-metallization annealing. The MOD-derived SrBi_2.4(Ta_0.75Nb_0.25)₂O₉ film did not exhibit the polarization fatigue after 10¹¹ switching cycles at ±5 V.     

Nonlinear electrical characteristics and dielectric properties of (Ca, Ta)-doped TiO2 ceramics

TiO₂ ceramics doped with 1.0 mol% Ca and different concentrations of Ta were obtained by sintering processing at 1450°C. The microstructures, nonlinear electrical behavior and dielectric properties of the ceramics were investigated. The samples have nonlinear coefficients of = 2.0–5.0 and ultrahigh relative dielectric constants which is up to 10⁵. Especially, the effects of Ta dopant on the nonlinear electrical characteristics and dielectric properties of the (Ca, Ta)-doped TiO₂ ceramics were studied in detail. When the concentration of Ta is 2.0 mol%, the sample exhibits the highest nonlinear coefficient and a comparatively lower dielectric constant. By analogy to a grain-boundary atomic defect model, the effects of Ta and the nonlinear electrical behavior of the TiO₂ system were explained.     

金属有机物分解法制备SrBi2Ta2O9铁电薄膜的开关特性

用金属有机物分解（MOD）以及sol-gel方法制备了SiBi2Ta2O9（STB）铁电薄膜。经测量在750℃晶化的SBT薄膜具有很好的铁电性能。通过对SBT样品极化反转过程进行测试,得出了外加电压（0．5－5V）与SBT薄膜的开关时间（100－600ms）及极化反转电荷的关系。并研究了不同气氛不退火对SBT铁电薄膜形状特性的影响。     

Cr2O3对(Co,Ta)掺杂的SnO2压敏电阻电学特性的影响

研究了Cr对(Co,Ta)掺杂的SnO2压敏材料电学性质的影响.当Cr2O3的含量从0增加到0.15mol%时,(Co,Ta)掺杂SnO2压敏电阻的击穿电压从206V/mm增加到493V/mm;1kHz时的相对介电常数从1968猛降至498;晶界势垒高度分析表明,SnO2晶粒尺寸的迅速减小是样品击穿电压增高、相对介电常数急剧降低和电阻率迅速增大的主要原因.对Cr含量增加引起SnO2晶粒减小的原因进行了解释.掺杂0.15mol% Cr2O3的SnO2压敏电阻非线性系数为24,击穿电压达498V/mm,在高压保护领域有很好的应用前景.     

熔盐法合成SrBi2Ta2O9粉体

采用熔盐法合成了纯的 系层状结构的ＳｒＢｉ_２Ｔａ_２Ｏ_９粉体．采用ＸＲＤ和ＳＥＭ等手段对粉体的结构和形态进行了分析,并与固相法进行了比较,结果表明熔盐法所得粉体形状呈片状,无团聚现象．对影响粉体颗粒尺寸和形状的因素进行了考查,并对熔盐法合成ＳｒＢｉ_２Ｔａ_２Ｏ_９粉体的机理进行了讨论．     

Co-precipitation technique for the preparation of nanocrystalline ferroelectric SrBi2Ta2O9

A simple co-precipitation technique had been successfully applied for the preparation of pure ultrafine single phase SrBi₂Ta₂O₉. Ammonium hydroxide was used to precipitate Sr²⁺, Bi³⁺ and Ta⁵⁺ cations simultaneously. No pyrochlore phase was found while heating powder at 800 °C and pure SrBi₂Ta₂O₉ phase was found to be formed by X-ray diffraction. Particle size and morphology was studied by scanning electron spectroscopy. Ferroelectric hysteresis loop parameters of these samples were also studied.     

Ta2O5薄膜的结构和电学性能研究

采用紫外光诱导热丝CVD沉积技术制备Ta2O5薄膜和Al/Ta2O2/SiMOS电容。利用XRD，AFM测试分析方法研究了紫外光源功率对Ta2O5薄膜结构的影响；通过C-V和，I-V测试对Ta2O5薄膜的介电常数，击穿场强和漏电流等电学性能进行了研究，结果表明：紫外光源的功率越大，Ta2O5薄膜的结晶性越好，介电常数越大，最大值为29，但紫外光功率对击穿场强和漏电流没有明显改善。     

织构化SrBi2Nb2O9陶瓷的制备工艺研究

以熔盐法合成各向异性的片状单相SrBi2Nb2O9 (SBN) 陶瓷粉体作为模板,采用模板晶粒生长(TGG)技术成功得制备出织构化SrBi2Nb2O9 (SBN) 陶瓷.通过SEM和XRD分析了烧结制度及模板尺寸对SBN陶瓷晶粒取向率的影响.结果表明,晶粒取向率随着烧结温度、烧结时间、升温速率、模板尺寸的升高而升高.合理控制制备工艺可获得晶粒取向率为0.89的高度织构化SBN陶瓷.织构化SBN陶瓷的相对体积密度随着模板平均粒径的增加而降低.在高温阶段,片状SBN模板晶粒消耗周围的基体粉体沿着流延方向生长,从而最终得到晶粒高度定向的陶瓷.