In situ observation of phase transition in perovskite compounds by high-resolution synchrotron radiation powder diffractometry

La_<2/3> tio_3基prov钛矿结构化合物是无线技术和SOFC（固体氧化物燃料电池）的有吸引力的材料，利用其优异的电性能。电学性质与钙钛矿固溶体的晶体结构密切相关。由于传统实验室衍射仪的角度分辨率较低，本论文报告了正交-四方相变，并指出了在文献中尚未确定的精确的单位细胞参数。这封信还表明，高分辨率同步加速器衍射技术是非常强大的研究温度依赖的单位电池参数，甚至接近转变点。这是值得发表的，因为大多数以前的同步加速器衍射工作致力于成分的依赖。我们用3台x射线粉末衍射仪（~d/d分辨率分别为0.03%、0.06%和0.10%）原位研究了双钙钛矿结构La_<0.64>(Ti_<0.92>,Nb_<0.08>)O_3中正交相和四方相之间的连续转变。d和~d表示λ/(2=sinθ)和峰宽，其中λ和θ为x射线波长和Bragg角。只有~d/d =0.03%的最高分辨率衍射仪能够在327 ~ 339βC的温度范围内检测到400 ~ 040个反射峰之间的分裂。结果表明，随着~d/d值的减小，转变温度的精度显著提高。随着~d/d值的减小，400和040反射峰分裂处的最高温度增加，而幂律决定的转变温度降低。

La_<2/3>TiO_3-based provskite-stractured compounds are attractive materials for both wireless technologies and SOFC (Solid Oxide Fuel Cells) utilizing their excellent electrical properties. The electrical properties are strongly dependent on crystal structure of the perovskite solid solutions. The present letter reports the orthorhombic-tetragonal phase transition, remarking the precise unit-cell parameters that have not been determined in the literature, due to the lower angular resolution of the conventional laboratory-based diffractometer. This letter also demonstrates that the high-resolution synchrotron diffraction technique is very powerful to study the temperature dependence of the unit-cell parameters even near the transition point. This is worth publishing, because most of previous synchrotron diffraction works devoted to the compositional dependence.We have investigated in situ a continuous transition between the orthorhombic and tetragonal phases in double-perovskite-structured La_<0.64>(Ti_<0.92>,Nb_<0.08>)O_3 by three X-ray powder diffractometers with different ~d/d resolutions of 0.03%, 0.06% and 0.10%. The d and ~d denote the λ/(2=sinθ ) and peak width where λ and θ are wavelength of X-ray and Bragg angle. Only the highest-resolution diffractometer of ~d/d =0.03% was able to detect the peaks splitting between 400 and 040 reflections, in the temperature range of 327βC to 339βC. It was found that the accuracy of the transition temperature is considerably improved with decreasing of ~d/d value. The maximum temperature where the peak splitting between 400 and 040 reflections is detectable increases, while the transition temperature determined by a power law decreases with decreasing of ~d/d value.