Anomalous octahedral distortion and multiple phase transitions in the metal-ordered manganite YBaMn2O6
Anomalous octahedral distortion and multiple phase transitions in the metal-ordered manganite YBaMn2O6
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DOI：
10.1016/j.jssc.2003.10.003
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发表时间：
2004-03-01
影响因子：
3.3
通讯作者：
Ueda, Y
中科院分区：
文献类型：
--
作者：
Nakajima, T;Kageyama, H;Ueda, Y
利用粉末X射线衍射、粉末中子衍射和透射电子显微镜（TEM）研究了金属有序锰氧化物YBaMn_2O_6的晶体结构。高温金属相（T-cl = 520 K <T）在具有以下晶胞的三斜晶系P1中结晶：Z = 2。a = 5.4948（15）埃，B = 5.4920（14）埃，c = 7.7174（4）埃，α = 89.804（20）度，β = 90.173（20）度，γ = 91.160（4）度。MnO6八面体倾斜近似写为a（0）B（-）c（-），导致ab平面内的显著结构各向异性。T-c2 <T <T-c1的结构是单斜P2（Z = 2，5.5181（4）埃，B = 5.5142（4）埃，c = 7.6443（3）埃，β = 90.267（4）度），具有a（-）B（-）c（-）倾斜。结构特征表明其具有d（x2）-（y2）轨道序（OO）。低于T-c2 = 480 K，晶体学上不等价的两个八面体显示出明显的体积差异，由于Mn 3 +/Mn 4+电荷有序。TEM研究进一步揭示了独特的d（3x2-r2）/d（3y2-r2）OO与修改的CE结构。结果发现，所获得的晶体结构是强烈相关的不寻常的物理性质。特别是，极高的温度下，电荷自由度冻结，T-C2，应该是由结构紊乱的情况下，严重扭曲的MnO 6八面体。(C)2003年爱思唯尔公司All rights reserved.
By means of powder X-ray diffraction, powder neutron diffraction and transmission electron microscopy (TEM), we determined the crystal structures of a metal-ordered manganite YBaMn2O6 which undergoes successive phase transitions. A high-temperature metallic phase (T-cl = 520 K < T) crystallizes in a triclinic P1 with the following unit cell: Z = 2. a = 5.4948(15) Angstrom, b = 5.4920(14) Angstrom, c = 7.7174(4) Angstrom, alpha = 89.804(20)degrees, beta = 90.173(20)degrees, gamma = 91.160(4)degrees. The MnO6 octahedral tilting is approximately written as a(0)b(-)c(-) leading to a significant structural anisotropy within the ab plane. The structure for T-c2 < T < T-c1 is a monoclinic P2 (Z = 2, 5.5181(4) Angstrom, b = 5.5142(4) Angstrom, c = 7.6443(3) Angstrom, beta = 90.267(4)degrees) with an a(-)b(-)c(-) tilting. The structural features suggest a d(x2)-(y2) orbital ordering (OO). Below T-c2 = 480 K, crystallographically inequivalent two octahedra show distinct volume difference, due to the Mn3+/Mn4+ charge ordering. The TEM study furthermore revealed a unique d(3x2-r2)/d(3y2-r2) OO with a modified CE structure. It was found that the obtained crystal structures are strongly correlated to the unusual physical properties. In particular, the extremely high temperature at which charge degree of freedom freezes, T-c2, should be caused by the absence of the structural disorder and by heavily distorted MnO6 octahedra. (C) 2003 Elsevier Inc. All rights reserved.