High-Temperature Synchrotron X-Ray Powder Diffraction Study of the Orthorhombic–Tetragonal Phase Transition in La0.63(Ti0.92,Nb0.08)O3
High-Temperature Synchrotron X-Ray Powder Diffraction Study of the Orthorhombic–Tetragonal Phase Transition in La0.63(Ti0.92,Nb0.08)O3
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La0.63(Ti0.92,Nb0.08)O3 正交-四方相变的高温同步辐射X射线粉末衍射研究
DOI：
10.1006/jssc.2001.9447
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发表时间：
2002
影响因子：
5.4
通讯作者：
S. Sasaki
中科院分区：
文献类型：
--
作者：
R. Ali;M. Yashima;Masahiko Tanaka;H. Yoshioka;Takeharu Mori;S. Sasaki
通过对23°C下收集的CuK-αX射线粉末衍射数据的Rietveld分析，对La0.63(Ti0.92，Nb0.08)O3的晶体结构进行了修正，该材料具有A位缺陷的正交钙钛矿型结构，沿c轴具有双理想钙钛矿AB3单元(空间群Pmmm，Z=2，a=3.86036(5)A，b=3.87222(5)A，c=7.82609(9)A)。用1.37873(3)A同步辐射X射线粉末衍射仪在25~496℃的温度范围内对同一样品的晶格参数进行了原位测量。同步加速器X射线粉末衍射技术被发现是非常强大的，可以在相变温度附近确定精确的晶格参数。该化合物在370℃左右表现出正交相和四方相之间的可逆相变。(1)晶格参数随温度的升高而增大，而b/a比随温度的升高而减小，并在正交-四方相转变点处趋于一致。(2)晶格参数值在加热和冷却之间没有观察到滞后现象。(1)和(2)的这些结果表明，正交-四方相变是连续的。
Abstract The crystal structure of La 0.63 (Ti 0.92 ,Nb 0.08 )O 3 has been refined by the Rietveld analysis of Cu Kα X-ray powder diffraction data collected at 23°C. This material was confirmed to have an A -site deficient orthorhombic perovskite-type structure with double ideal perovskite AB O 3 units along the c -axis (space group Pmmm , Z =2, a =3.86036(5) A, b =3.87222(5) A, c =7.82609(9) A). Lattice parameters of the same sample have been investigated in situ in the temperature range from 25°C to 496°C by 1.37873(3) A synchrotron X-ray powder diffraction. The synchrotron X-ray powder diffraction technique was found to be very powerful to determine precise lattice parameters around a phase transition temperature. This compound exhibited a reversible phase transition between the orthorhombic and tetragonal phases at around 370°C. (1) The lattice parameters increased continuously with temperature, while the b / a ratio decreased continuously with temperature and became unity at the orthorhombic–tetragonal transition point. (2) No hysteresis was observed in the lattice parameter values between heating and cooling. These results of (1) and (2) suggest that the orthorhombic–tetragonal phase transition is continuous.