THE LAYERED PEROVSKITES (C3H7NH3)2MNCL4(PAMC), AND (C2H5NH3)2MNCL4(EAMC) - BIREFRINGENCE STUDIES AND THE SYMMETRY OF THE COMMENSURATELY MODULATED EPSILON PHASE OF PAMC
THE LAYERED PEROVSKITES (C3H7NH3)2MNCL4(PAMC), AND (C2H5NH3)2MNCL4(EAMC) - BIREFRINGENCE STUDIES AND THE SYMMETRY OF THE COMMENSURATELY MODULATED EPSILON PHASE OF PAMC
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DOI：
10.1107/s0567739482000242
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发表时间：
1982-01-01
期刊：
影响因子：
--
通讯作者：
DEPMEIER, W
中科院分区：
文献类型：
--
作者：
BRUNSKILL, IH;DEPMEIER, W
通过测量PAMC（001）血小板的双折射随温度的变化，证实了先前确定的相变。根据以前的热分析研究，通过正态-不相称的δ→γ转变和正态-相称的ζ→β转变的影响很大，而公度-正态- δ→δ和不相称-正态γ→β转变的影响较小。并与类似的EAMC研究进行了比较。从钙钛矿型层结构变化的角度讨论了这两种化合物的光学各向异性。在适当的地方，使用Δn ~(1—T/Tc)2β形式的幂定律来描述双折射。通过分析主反射和卫星反射之间的系统消光，提出PAMC的相位是δ相位的（3 + 1）维相应调制版本。超空间组确定为PAbmas_{{\bar 1}}1。由于调制矢量的合理性，导致了三维空间群Pbma。
By measuring the birefringence on (001) platelets of PAMC as a function of temperature, previously determined phase transitions have been confirmed. Large effects were measured on passing through the normal-incommensurate δ → γ transition and through the normal-commensurate ζ → ɛ transition, whereas the commensurate-normal ɛ → δ and the incommensurate-normal γ → β transitions are less pronounced, in accordance with former thermoanalytic studies. A comparison is made with a similar study on EAMC. The optical anisotropy is discussed for both compounds in terms of the structural changes of the perovskite-type layers. Power laws of the form Δn ~ (1 -- T/Tc)2β are used to describe the birefringence where appropriate. By analyzing systematic extinctions amongst main and satellite reflexions, the ɛ phase of PAMC is proposed to be a (3 + 1)-dimensional commensurately modulated version of the δ phase. The superspace group is determined to be PAbmas_{{\bar 1}}1. With the rationality of the modulation vector this leads to the three-dimensional space group Pbma.