TEM study of the electron-doped layered La2-2xCa1+2xMn2O7:: Orthorhombic phase in the 0.8<x<1.0 composition range
TEM study of the electron-doped layered La2-2xCa1+2xMn2O7:: Orthorhombic phase in the 0.8<x<1.0 composition range
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DOI：
10.1006/jssc.2000.9068
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发表时间：
2001-03-01
影响因子：
3.3
通讯作者：
Greenblatt, M
中科院分区：
文献类型：
--
作者：
Bendersky, LA;Chen, RJ;Greenblatt, M
采用柠檬酸凝胶法合成了一系列n = 2，化学计量量为La2-2xCa1+2xMn2O7的Ruddlesden-Popper化合物，并用TEM研究了其组成范围为0.8 < x < 1.0。原位实验和亚结构/孪晶分析确定了低温（200-350度）下14/mmm相的结构变化，互反空间分析确定了超晶格反射（以前未被X射线检测到）和可能的空间群。低温相属于非中心对称Cmc2(1)或Ama2空间群，也可能存在瞬态Cmcm空间群。这些结构转变与在室温下发生的磁转变不一致。针对Cmcm和Cmc2(1)提出了一种基于近刚性八面体倾斜的结构模型。提出的低温Cmc2(1)相模型具有Phi Phi Psi (z)/Phi Phi Psi (z)组合倾斜，而瞬态Cmcm具有Phi Phi0/Phi Phi0组合倾斜。(C) 2001学术出版社
A series of Ruddlesden-Popper compounds with n = 2 and stoichiometry La2-2xCa1+2xMn2O7 were synthesized by a citrate gel technique and studied by TEM for the composition range 0.8 < x < 1.0. In situ experiments and analysis of substructure/twins identified structural changes of the 14/mmm phase at low temperatures (200-350 degreesC), Reciprocal space analysis identified superlattice reflections (not previously detected by X ray) and possible space groups. The low-temperature phase belongs to the noncentrosymmetric Cmc2(1) or Ama2 space group, and the transient Cmcm space group is also possible. These structural transitions do not coincide with the magnetic transitions, which occur below room temperature. A structural model based on tilting of almost-rigid octahedra is suggested for Cmcm and Cmc2(1). The proposed model for the low-temperature Cmc2(1) phase has a Phi Phi Psi (z)/Phi Phi Psi (z) combination of tilts, while the transient Cmcm has a Phi Phi0/Phi Phi0 combination of tilts. (C) 2001 Academic Press