Domain Structure and Phase Symmetry of Multiferroic BiFeO3-PbTiO3 Single Crystals Studied by Piezoresponse Force Microscopy

Piezoresponse force microscopy (PFM) was used to investigate the domain structure of multiferroic BiFeO₃- PbTiO₃ single crystals with morphotropic phase boundary (MPB) compositions. The PFM data demonstrate the piezoelectricity and the PFM domain responses under the designed experimental setup reveal the coexistence of a rhombohedral, a tetragonal, and an orthorhombic phases in the MPB crystals, which is consistent with the results of structural refinements based on X-ray diffraction data.     

硅基Bi4Ti3O12薄膜的C-V特性研究

Bi4 Ti3O12是典型的层状钙钛矿结构铁电材料,具有优良的压电、铁电、热释电和电光等性能,可广泛应用于铁电存储器、压电和电光等器件.本文在硅衬底上利用溶胶凝胶法制备出Bi4 Ti3O12铁电薄膜,并且对其性能进行了研究.测量不同退火温度下得到的Ag/BTO/p-Si结构的C-V曲线,结果表明Bi4 Ti3O12薄膜在合适的制备工艺下可望实现极化型存储.     

Bi4Ti3O12铁电薄膜的MOCVD制备及其物理性质研究

采用常压ＭＯＣＶＤ技术在（１００）硅衬底上生长了具有（１００）及（００１）取各的钛酸铋（Ｂｉ４Ｔｉ３Ｏ１２）薄膜。在适当的生长条件下可获得（１００）取向膜，在７５０－８００℃下退火可获得（００１）择优取向膜。通过观察Ｐ－Ｅ电滞回线可确认膜的铁电性质，测得（１００）取向膜的剩余极化强度为３８μｃ／ｃｍ＾２，矫顽场为４５ＫＶ／ｃｍ。同时测量了钛酸铋薄膜的介电常数及损耗角正切。     

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.     

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℃.     

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。     

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℃.     

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.     

Increasing visible-light absorption for photocatalysis with black 2D Bi4Ti3O12 nanosheets

In this work, a simple method to prepare defect two-dimension (2D) Bi₄Ti₃O₁₂ nanosheets material by NaBH₄ reduction with Argon atmosphere was reported. The results of EPR and XPS demonstrated that the presence of oxygen vacancy in Bi₄Ti₃O₁₂, which resulted in color changed and extend photon-absorbance. By comparing to pristine Bi₄Ti₃O₁₂, the black Bi₄Ti₃O₁₂ exhibited higher photocatalytic activity to pollutants. The mechanism was also proposed for exploring the defect in the photocatalytic process.     

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℃.     

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.     

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.     

Effect of Bi2Ti2O7 Seeding Layer on Capacitance-voltage Properties of Bi3:54Nd0:46Ti3O12 Films

Au/Bi3:54Nd0:46Ti3O12/Bi2Ti2O7/Si structure has been fabricated with a preferentially (111)-orientated Bi2Ti2O7 seeding layer as a ferroelectric gate of metal-ferroelectric-insulator ¯eld e®ect transistor. Bi3:54Nd0:46Ti3O12 and Bi3:54Nd0:46Ti3O12/Bi2Ti2O7 ¯lms are both well-crystallized when annealed at 680±C for 40 min, and have smooth, dense and crack-free surfaces. The width of memory window of the ferroelectric gate increases with increasing electric ¯eld applied to the Bi3:54Nd0:46Ti3O12 thin ¯lms. The width of memory window of Au/Bi3:54Nd0:46Ti3O12/Bi2Ti2O7/Si with seeding layer is relatively wider than that of Au/Bi3:54Nd0:46Ti3O12/Si at the same bias voltage, and the counterclockwise hysteresis curve of Au/Bi3:54Nd0:46Ti3O12/Bi2Ti2O7/Si is referred to as polarization type switching at di®erent voltages. Bi2Ti2O7 seeding layer plays an important role in alleviating the element interdi®usion between Bi3:54Nd0:46Ti3O12 and Si.     

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.     

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.     

Preparation and sintering behaviour of submicronic Bi4Ti3O12 powders

Submicronic powders of Bi₄Ti₃O₁₂ with different morphologies were prepared by both the oxalate coprecipitation and the conventional mixing oxides methods. Compacts of the two calcined powders were sintered at 850–1100 °C in air, and the densification process was studied by non-isothermal and dilatometric experiments. A rapid densification (> 97% theoretical density) below 875 °C took place in the Bi₄Ti₃O₁₂ oxalate powder which was attributed to an extremely uniform pore-size distribution in the green compact. The possible formation of a transient liquid which promotes densification also was taken into account. The development of plate-like morphology in the conventional Bi₄Ti₃O₁₂ powder, broad pore-size distribution, and the plate-like colony formation, hindered rapid densification of the green compacts at low temperature. Microstructural development was studied; preliminary dielectric and electrical results are also reported.     

Dy3+掺杂Bi4Si3O12晶体生长及其热释光特性

采用坩埚下降法生长了Dy³⁺掺杂浓度分别为0.1mol%、0.2mol%、0.3mol%、2mol%、3mol%和4mol%的Bi₄Si₃O₁₂(BSO)晶体。发现高浓度(2mol%以上)掺杂能够显著改变BSO晶体的析晶行为, 晶体表面析出物完全消失, 顶部呈现光滑结晶面; 低浓度(低于0.3mol%)掺杂能够显著提高晶体的光输出, 最高可达纯BSO的145%。晶体热释光谱测试结果表明: 少量Dy³⁺掺杂虽然热释光峰略有增强, 但有利于晶体光产额的提高; 高浓度掺杂则容易引起晶格畸变, 甚至产生新的缺陷, 降低晶体的光产额。