用高分辨透射电子显微技术研究0.94(Na_(1/2)Bi_(1/2))TiO_3–0.06BaTiO_3的有序结构

ORDERED STRUCTURE OF 0.94(Na_(1/2)Bi_(1/2))TiO_3-0.06BaTiO_3 INVESTIGATED BY THE HIGH RESOLUTION TRANSMISSION ELECTRON MICROSCOPY

用高分辨透射电子显微技术(high resolution transmission electron microscopy,HRTEM)和选区电子衍射(selected area electron diffraction,SAED)技术对具有A位复合钙钛矿结构的0.94(Na1/2Bi1/2)TiO3(BNT)–0.06BaTiO3(BNBT6)陶瓷的显微结构进行了深入研究。沿[001],[011]和[111]3个晶带轴方向的SAED花样分析结果表明:A位Bi3+和Na+可以形成2种不同的有序结构——1/2{110}和1/2{111}超结构。据此,建立了BNT的1/2{110}和1/2{111}有序结构模型,其中1/2{110}型有序是由Bi3+层和Na+层沿[110]方向交替排列而形成,1/2{111}型有序是由Bi3+层和Na+层沿[111]方向交替排列而形成。利用多层法,通过计算机模拟了1/2{111}有序结构沿[001],[011]和[111]3个方向的HRTEM像,与实验拍摄的HRTEM像对照,验证了所建立的1/2{111}有序结构模型的正确性。同时,采用快速Fourier变换(fast Fourier transformation,FFT)技术,由1/2(330)和1/2(330)超晶格反射斑点获得的一维晶格像,揭示了沿[110]方向局部Bi3+层和Na+层扭曲导致的位错和反相畴界(anti-phase boundary,APB),APB的存在表明结构中存在着Bi3+层和Na+层沿[110]方向的交替排列,证实BNBT6中存在着1/2{110}有序结构。BNBT6有序结构的HRTEM研究表明:A位Bi3+和Na+的化学有序是导致超晶格反射的主要原因。

The microstructures of A-site complex perovskite structure 0.94（Na1/2Bi1/2）TiO3（BNT）-0.06BaTiO3 （BNBT6） ceramics were extensively studied by the high resolution transmission electron microscopy （HRTEM） and selected area electron diffraction （SAED） techniques. The SAED patterns of BNBT6 specimens from the [001], [011] and [111] directions show that there are 1/2{110} and 1/2 { 111 } superstructure reflections caused by Bi^3＋ and Na^＋ at the A-site. According to the analytical results of the SAED patterns, the 1/2 { 110} and 1/2 { 111 } ordered structural models of BNT were established. The 1/2 { 110} ordered structural model was formed by the alternate arrangement of Bi^3＋ and Na^＋ layers along the [ 110] direction, and the 1/2 { 111 } ordered structural model was formed by the alternate arrangement of Bi^3＋ and Na^＋ layers along the [111] direction. The multi-layer technique was employed for computer-aided simulation of HRTEM images of BNT 1/2 { 111 } ordered structure along the [001], [011] and [111] directions. Compared with the experimental HRTEM images, the computer simulation confirmed the validity of the established 1/2 { 111} ordered structural model. At the same time, a one-dimensional lattice image was obtained from 1/2（330） and 1/2 （3 30） super lattice reflections using the fast Fourier transformation （FFT） technique. The image shows the dislocations and anti-phase boundaries （APB） caused by displacement of local Bi^3＋, Na^＋ layers along the [110] direction. The existence of APB indicates that there is an alternate arrangement of Bi^3＋ and Na＋ layers along the [110] direction, which confirms the existence of a 1/2 { 110} ordered structure. The results of the ordered structure of BNBT6 by FIRTEM indicate that the chemical ordering of Bi^3＋ and Na^＋ at the A-site is the main reason for the super lattice reflections.