Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO3
Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO3
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DOI：
10.1021/ja0664032
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发表时间：
2007-01-31
影响因子：
15
通讯作者：
Takayama-Muromachi, Eiji
中科院分区：
文献类型：
--
作者：
Belik, Alexei A.;Iikubo, Satoshi;Takayama-Muromachi, Eiji
采用选区电子衍射（SAED）、会聚束电子衍射（CBED）和Rietveld方法研究了在6 GPa和1383 K下制备的单相BiMnO 3多晶样品的结构特性。SAED和CBED数据表明，BiMnO 3在300 K时属于中心对称空间群C2/c。在300 K时的晶体学数据为：a = 9.5415（2）A，B = 5.61263（8）A，c = 9.8632（2）A，β = 110.6584（12）度; a = 9.5866（3）A，B = 5.59903（15）A，c = 9.7427（3）A，β = 108.601（2）度，550 K，Z = 8，空间群C2/c。Mn-O键长的分析表明，在300 K时BiMnO_3中存在的轨道序高于T-OO = 474 K时的轨道序。474 K时的相变为一级相变，伴随着磁化强度的跃变和有效磁矩及韦斯温度的微小变化，在300-450 K时，μ（eff）= 4.69 μ（B），θ = 138.0 K;在480-600 K时，μ（eff）= 4.79 μ（B），θ = 132.6 K。
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 T-OO = 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, mu(eff) = 4.69 mu(B) and theta = 138.0 K at 300-450 K and mu(eff) = 4.79 mu(B) and theta = 132.6 K at 480-600 K.