Qiu Xiangyun, Proffen Th, Mitchell J F, Billinge S J L
Department of Physics and Astronomy, Michigan State University, E. Lansing, Michigan 48824, USA.
Phys Rev Lett. 2005 May 6;94(17):177203. doi: 10.1103/PhysRevLett.94.177203. Epub 2005 May 5.
The local and intermediate structure of stoichiometric LaMnO3 has been studied in the pseudocubic and rhombohedral phases at high temperatures (300-1150 K). Neutron powder diffraction data were collected and a combined Rietveld and high real space resolution atomic pair distribution function analysis was carried out. The nature of the Jahn-Teller (JT) transition around 750 K is confirmed to be orbital order to disorder. In the high-temperature orthorhombic (O) and rhombohedral (R) phases, the MnO6 octahedra are still fully distorted locally. More importantly, the intermediate structure suggests the presence of local ordered clusters of diameter approximately 16 A ( approximately 4 MnO6 octahedra) implying strong nearest-neighbor JT antiferrodistortive coupling. These clusters persist well above the JT transition temperature even into the high-temperature R phase.
在高温（300 - 1150 K）下，对化学计量比的LaMnO₃在伪立方相和菱面体相中的局部和中间结构进行了研究。收集了中子粉末衍射数据，并进行了Rietveld精修和高真实空间分辨率原子对分布函数分析相结合的研究。证实了750 K左右的 Jahn - Teller（JT）转变的本质是轨道有序到无序。在高温正交（O）相和菱面体（R）相中，MnO₆八面体在局部仍然完全扭曲。更重要的是，中间结构表明存在直径约为16 Å（约4个MnO₆八面体）的局部有序团簇，这意味着存在强烈的最近邻JT反铁畸变耦合。即使在JT转变温度以上直至高温R相，这些团簇依然存在。
