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

La 2/3 TiO 3基钙钛矿结构化合物由于其优异的电学性能，在无线电技术和固体氧化物燃料电池（SOFC）领域都有着广泛的应用前景。钙钛矿固溶体的电性能强烈依赖于晶体结构。本信报告的正交-四斜晶系相变，remarking精确的晶胞参数，尚未确定在文献中，由于较低的角分辨率的传统的实验室为基础的衍射仪。这封信还表明，高分辨率的同步辐射衍射技术是非常强大的研究单位电池参数的温度依赖性，即使在转变点附近。我们<0.64><0.92><0.08>用三台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_（Ti_，Nb_）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是X射线的波长和布拉格角。在327 - 339 ℃温度范围内，只有最高分辨率的衍射仪（~d/d =0.03%）才能检测到400 - 040次反射之间的峰分裂。结果表明，随着~d/d值的减小，相变温度的准确性有了很大的提高。随着~d/d值的减小，400 ~ 040反射峰分裂处的最高温度升高，而由幂律确定的转变温度降低。

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.