Sandwiched BaNd2Ti4O12/Bi4Ti3O12/BaNd2Ti4O12 ceramics prepared by spark plasma sintering

Spark plasma sintering (SPS) combined with heat treatment was investigated to prepare laminated ceramics from compositions having quite different sintering temperatures. Although the optimal sintering temperature of BaNd₂Ti₄O₁₂ (BNT) ceramics was much higher than that of Bi₄Ti₃O₁₂ (BIT) ceramics, sandwiched BaNd₂Ti₄O₁₂/Bi₄Ti₃O₁₂/BaNd₂Ti₄O₁₂ (BNT/BIT/BNT) composite ceramics were successfully prepared with this new method. The results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the BNT layers and the BIT layer were well bonded and no significant diffusion between them was observed. The temperature coefficient of dielectric constant of the laminated ceramic was found to be much smaller than that of BNT ceramic.     

Sintering and characterization of Bi4Ti3O12 ceramics

Polycrystalline ferroelectric Bi₄Ti₃O₁₂ ceramics have been prepared by the method of reactive liquid phase sintering. The sintering behaviour of the Bi₂O₃-TiO₂ composite was examined by plotting the isothermal densification curves. The results indicate that the starting oxides are involved in the reaction even at temperatures lower than or equal to 800°C, but the reaction advances at a very slow rate. Above solidus, the liquid phase promotes an extended reaction. Saturation observed in two densification curves, at 875 and 1100°C demonstrate that the reaction proceeds by two steps. A completion of the Bi₄Ti₃O₁₂ formation occurs after 60 min of sintering at 1100°C. Optical micrographs of sintered bismuth titanate ceramics show randomly oriented ferroelectric grains separated by a paraelectric intergranular layer. The Bi₄Ti₃O₁₂ crystallites exhibit a platelike morphology, similar in the appearance to mica, as evidenced by scanning electron micrographs. Isothermal annealing (750 to 950°C) does not affect the microstructure and electric properties of sintered bismuth titanate. The considerable value of dielectric permittivity and the appearance of hysteresis have been correlated to the presence of oxygen vacancies within the pseudotetragonal structure of Bi₄Ti₃O₁₂. The oxygen vacancies are preferentially sited in the vicinity of bismuth ions as evidenced by X-ray photoemission data. XPS and AES measurements confirm that the surface concentration of cations comprising the Bi₄Ti₃O₁₂ ceramics does not deviate from the nominal bulk composition.     

Ag@AgCl改性Bi4Ti3O12的制备及其可见光催化性能

以五水硝酸铋为铋源、钛酸四丁酯为钛源,通过水热法制备了Bi4Ti3O12,再以硝酸银为银源、盐酸为氯源,采用光照还原Bi4Ti3O12得到Ag@AgCl/Bi4Ti3O12复合材料.利用XRD、UV-Vis DRS、SEM、TEM、BET和XPS等方法对所制备材料的组成和结构进行表征和分析,并以甲基橙(MO)溶液的脱色...     

硅衬底Bi4Ti3O12和Bi3.25La0.75Ti3O12铁电薄膜的慢正电子束研究

对硅衬底生长的Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜样品测量了慢正电子多普勒展宽谱,得到了S参数随正电子注入能量的变化。通过对S参数和W参数的分析,讨论了这类材料中的捕获态特征和结构特点,结果表明,薄膜与硅衬底界面的缺陷为空位-氧复合体,La的掺杂有助于阻止空位-氧复合体向界面的扩散。     

非化学计量Bi2O3对制备Bi4Ti3O12粉体影响的研究

制备晶粒形貌生长各向异性的中间化合物Bi4Ti3O12粉体是采用流延成型和模板晶粒生长(TGG)等工艺方法制备(Na0.5Bi0.5)TiO3基无铅压电织构陶瓷的关键技术.以NaCl-KCl熔盐法制备了生长各向异性的Bi4Ti3O12粉体,利用X射线衍射和扫描电子显微镜研究了非化学计量Bi2O3对粉体相结构和微观形貌的影响,优化了制备Bi4Ti3O12粉体的工艺参数,并探讨了Bi4Ti3O12粉体在熔盐中的生长机理.研究表明,随着Bi2O3过量程度的增加,所得Bi4Ti3O12粉体颗粒的平均尺寸和均匀程度均增加,当Bi2O3过量7.5%时达到最佳值,其平均粒径为8～10 μm.     

Electro-mechanical behaviour of single domain single crystals of bismuth titanate (Bi4Ti3O12)

The piezoelectric constantsd ₁₁,d ₂₂ andd ₃₃ for a single domain single crystal of Bi₄Ti₃O₁₂ have been measured at room temperature using appropriate crystal cuts on a Berlincourtd ₃₃ meter. From the known temperature dependence of the spontaneous polarization, lattice strain and dielectric permittivity, the equivalent piezoelectric constants have been calculated assuming a simple proper ferroelectric in which,P _s, is the order parameter. Constants in the plane of the perovskite-like sheets in the Bi₄Ti₃O₁₂ structure (d ₁₁,d ₂₂) show good agreement with experimental values. The calculated value of the constantd ₃₃ is more than an order of magnitude larger than the experimentally-measured value and gives clear indication of the indirect coupling to the strain in the tetrad axial direction and the need for a more sophisticated phenomenology.     

Molten salt synthesis and luminescence properties of Bi4Si3O12 powders

In this paper, Bismuth silicate (Bi₄Si₃O₁₂, BSO) powders were prepared by reaction in molten salts (NaCl and KCl) using Bi₂O₃ and SiO₂ powders as raw materials. The effects of salt contents and excessive contents of Bi₂O₃ and SiO₂ were characterized by X-ray diffraction and scanning electron microscopy. The properties of Bi₄Si₃O₁₂ powders were analyzed via fluorescence spectroscopy. Forming mechanism of platelets was discussed. The experimental results suggest that Bi₄Si₃O₁₂ powders are produced at 780 °C for 4 h with 40 wt% salts and 5 wt% excessive content of Bi₂O₃. The peaks of excitation spectrum and emission spectrum for BSO powders are separately located at 266 and 457.6 nm. Compared with crystal materials, the excitation spectrum and emission spectrum of Bi₄Si₃O₁₂ powders indicate blue shift. Interface reacting mechanism can be used to explain the coarsening process of bismuth silicate platelets produced in molten salt synthesis. In addition, dissolution–precipitation mechanism also plays an important role in the synthesis of bismuth silicate platelets.     

Bi4Ti3O12的熔盐法制备及改性研究进展

综述了Bi4Ti3O12材料的最新研究进展,介绍了Bi4Ti3O12制备方法和改性技术的研究,对熔盐法制备、热锻、模板晶粒生长、丝网印刷等几种晶粒定向生长技术和A、B位掺杂及机理等方面的研究进行了系统评述,总结了目前Bi4Ti3O12研究中存在的问题,并对未来的研究方向进行了预测.     

熔盐法合成板状钛酸铋微晶

采用熔盐法制备了板状Bi4Ti3O12微晶.用示差扫描量热-热重分析(DSC-TG)、X射线衍射(XRD)及扫描电镜(SEM)研究了不同温度对合成Bi4Ti3O12相结构与形貌的影响.结果表明,板状Bi4Ti3O12微晶的最佳合成温度为800～1000℃,低于800℃合成产物中容易出现杂相;1030℃时Bi4Ti3O12出现结构变化;1165℃出现杂相Na0.5Bi0.5Ti7O27;温度继续升高到1250℃时Bi4Ti3O12出现分解.实现板状Bi4Ti3O12微晶形貌可控的最佳温度范围为850～950℃.     

Pressure dependence of the Raman-active modes in Bi4Ti3O12

Bismuth titanate (Bi₄Ti₃O₁₂), a layer-type ferroelectric material crystallizing in the monoclinic system, has been investigated by high-pressure Raman technique up to 17 GPa in a diamond anvil cell. A pressure-induced phase transition occurs near 3 GPa, and the softening of the lowest Raman mode near 31 cm⁻¹ seems to be associated with this transition. Furthermore, the Raman data as well as absorption measurements indicate that a second phase transition occurs near 11 GPa. This transition may be due to a change from the ferroelectric to the paraelectric phase under the influence of pressure.     

Nb掺杂Bi4Ti3O12层状结构铁电陶瓷的电行为特性研究

采用固相烧结工艺制备了Nb⁵⁺掺杂的Bi₄Ti₃O₁₂层状结构铁电陶瓷.运用XRD 和AFM对Bi₄Ti_3-xNb_xO_12+x/2材料的微观结构进行表征,发现所制备的陶瓷均具有单一的正交相结构,抛光热腐蚀表面晶粒的显微形貌表现为随机排列的棒状结构.通过对材料直流电导率与温度关系的Arrhenius拟合,分析丁Bi₄Ti_3-xNb_xO_12+x/2的导电机理. Nb⁵⁺掺杂提高了材料的介电常数,但居里温度随掺杂含量的增加呈线性下降趋势.DSC结果显示Bi₄Ti_3-xNb_xO_12+x/2材料在居里温度处经历了一级铁电相变.样品的铁电性能测试结果表明, Nb⁵⁺掺杂Bi₄Ti₃O₁₂提高了材料的剩余极化Pr,这主要是由于^_Nb5+取代Ti⁴⁺大大降低了材料中氧空位的浓度,使得氧空位对畴的钉扎作用减弱的缘故.     

Nd掺杂Bi4Ti3O12陶瓷的结构与性能研究

采用固相合成法制备了不同Nd掺杂量的Bi4-xNdxTi3O12(x=0～1.0)陶瓷.采用XRD分析了陶瓷样品的物相结构,采用SEM观察了陶瓷样品的显微结构特征,系统地评价了陶瓷样品的铁电性能.研究结果表明,经1100℃烧结样品结构致密、晶粒均匀.不同Nd掺杂量并未引起物相结构的改变,所有样品均为单一的层状钙钛矿结构.适量的Nd掺入会提升Bi4-xTi3O12陶瓷样品的铁电性能.     

Bi4Ti3O12掺杂BST陶瓷性能和结构的研究

采用固相法,利用X-射线衍射(XRD)、扫描电镜(SEM)等测试分析方法系统研究了Bi4Ti3O12掺杂量(质量分数,下同)(18％～50％)对(Ba0.71Sr0.29)TiO3 (BST)基电容器陶瓷介电性能和结构及烧结温度的影响.研究结果表明:随着Bi4Ti3O12掺杂量的增加,BST陶瓷的晶粒尺寸先减小然后增大.在BhTi3O12掺杂量的范围内,BST陶瓷的物相均为Bi4Ti3O12和BST的混合相,随着Bi4Ti3O12掺杂量的增加,Bi4Ti3O12相逐渐增多.随着Bi4Ti3O12掺杂量的增加,BST陶瓷的介电常数(ε)逐渐减小;介质损耗(tarδ)均较小(0.0050～0.0075),呈先减小后增大的趋势;烧结温度逐渐降低,当Bi4Ti3O12掺杂量为50％时,烧结温度为1090℃.随着Bi4Ti3O12掺杂量的增加,BST陶瓷的容温变化率(AC/C)绝对值在正温范围内(25～125℃)逐渐减小,容温变化率(△C/C)在负温范围内(-55～25℃)先减小然后上升再下降.当Bi4Ti3O12掺杂量为26％时,BST陶瓷综合性能较好,其介电常数为1700,介质损耗为0.006,容温变化率的绝对值小于15％(-55～125℃),符合X7R特性,耐直流电压为5.0kV/mm,烧结温度为1120℃.     

溶胶—凝胶技术制备Bi4Ti3O12铁电薄膜的研究

采用溶胶－凝胶技术在Ｓｉ单晶基片上制备了具有层状钙钛矿型结构的Ｂｉ４Ｔｉ３Ｏ１２ｘ铁电薄膜，讨论了回火温度与时间对薄膜结构的影响，Ｘ射线衍射分析表明，经７００℃和７００℃以上温度回火的薄膜为具有层状钙矿型结构的Ｂｉ４Ｔｉ３Ｏ１２多晶薄膜，该薄膜的电滞回线测试呈出剩余极化强度Ｐｒ＝５μＣ／ｃｍ＾２，矫顽场Ｅｃ＝１３０ｋＶ／ｃｍ。     

Properties of aurivillius phases in the Bi4Ti3O12-BiFeO3 system

A number of new Bi _m+1Fe _m?3TiO_3m+3 compounds with integer and fractional m values are identified in the Bi₄Ti₃O₁₂-BiFeO₃ system. All of the compounds are shown to have Aurivillius-type structures. The phase-transition and decomposition temperatures of the new and earlier known compounds of the Bi₄Ti₃O₁₂-BiFeO₃ system are determined. The linear thermal expansion coefficients of the synthesized compounds are evaluated using dilatometry, and their sintering onset temperatures are determined.     

A位掺杂Bi4Ti3O12陶瓷的铁电性能研究

用传统固相烧结工艺,制备了纯相的Bi4Ti3O12 (BTO)陶瓷,A位掺杂的Bi3.25La0.75Ti3O12(BLT),Bi3.15Nd0.85Ti3O12(BNdT)铁电陶瓷.X射线衍射结果表明,所有样品均为单一的层状钙钛矿结构,La、Nd掺杂未改变BTO的晶体结构.铁电测试结果表明,BTO、BLT和BNdT陶瓷的剩余极化2Pr值分别为12.4、23.8和39.4μC/cm2.A位掺杂后,BLT、BNdT的2Pr值比未掺杂的BTO分别提高了1.92和3.18倍.漏电流测试表明,BLT、BNdT陶瓷的漏电流密度比BTO明显降低.A位掺杂显著提高了BTO陶瓷的铁电性能.     

La掺杂的Bi4Ti3O12陶瓷的动态变温X射线衍射研究

利用动态变温X射线衍射技术,研究了La掺杂Bi4Ti3O12（BLT）陶瓷相的形成过程、微结构的变化及其与温度的关系。动态跟踪比较了不同物相的反应速率与消长规律。比较了大气与真空不同的气氛环境对BLT相结构形成的影响。初步给出了固态成相的温度范围和所需时间。     

熔盐法制备片状钛酸铋粉体的研究

采用NaCl-KCl熔盐法制备了生长各向异性的片状Bi4Ti3O12粉体.研究了预烧温度及熔盐含量对粉体形貌及显微结构的影响.结果表明,750℃预烧所得Bi4Ti3O12粉体为单一的钙钛矿型结构,随熔盐含量的增加,Bi4Ti3O12粉粒的尺寸及生长的各向异性程度均有所增大,预烧温度的增加也促进了粉粒的生长,获得明显生长各向异性的钛酸铋粉体的最佳预烧温度为950～1000℃.