BiMnO₃ 单斜晶系到单斜晶系相变的起源及中心对称晶体结构的证据
Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO3.
作者信息
Belik Alexei A, Iikubo Satoshi, Yokosawa Tadahiro, Kodama Katsuaki, Igawa Naoki, Shamoto Shinichi, Azuma Masaki, Takano Mikio, Kimoto Koji, Matsui Yoshio, Takayama-Muromachi Eiji
机构信息
Advanced Nano Materials Laboratory (ANML) and High Voltage Electron Microscopy Station (HVEMS), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
出版信息
J Am Chem Soc. 2007 Jan 31;129(4):971-7. doi: 10.1021/ja0664032.
Structural properties of polycrystalline single-phased BiMnO3 samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO3 crystallizes in the centrosymmetric space group C2/c at 300 K. The crystallographic data are a = 9.5415(2) A, b = 5.61263(8) A, c = 9.8632(2) A, beta = 110.6584(12) degrees at 300 K and a = 9.5866(3) A, b = 5.59903(15) A, c = 9.7427(3) A, beta = 108.601(2) degrees at 550 K, Z = 8, space group C2/c. The analysis of Mn-O bond lengths suggested that the orbital order present in BiMnO3 at 300 K melts above TOO = 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature, mueff = 4.69 microB and theta = 138.0 K at 300-450 K and mueff = 4.79 microB and theta = 132.6 K at 480-600 K.
通过选区电子衍射（SAED）、会聚束电子衍射（CBED）以及利用在300 K和550 K下测量的中子衍射数据的Rietveld方法，研究了在6 GPa和1383 K下制备的多晶单相BiMnO₃样品的结构性质。SAED和CBED数据表明，BiMnO₃在300 K时结晶于中心对称空间群C2/c。晶体学数据在300 K时为a = 9.5415(2) Å，b = 5.61263(8) Å，c = 9.8632(2) Å，β = 110.6584(12)°，在550 K时为a = 9.5866(3) Å，b = 5.59903(15) Å，c = 9.7427(3) Å，β = 108.601(2)°，Z = 8，空间群C2/c。对Mn - O键长的分析表明，BiMnO₃在300 K时存在的轨道有序在高于TOO = 474 K时熔化。474 K时的相变是一级相变，伴随着磁化强度的跃变以及有效磁矩和魏斯温度的微小变化，在300 - 450 K时mueff = 4.69 μB且θ = 138.0 K，在480 - 600 K时mueff = 4.79 μB且θ = 132.6 K。
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