相变
结晶学
化学
相(物质)
拉曼光谱
烷基
亚甲基
钙钛矿(结构)
量热法
衍射
有机化学
光学
凝聚态物理
热力学
物理
作者
Sudip Barman,N. V. Venkataraman,S. Vasudevan,Ram Seshadri
摘要
The single perovskite slab alkylammonium lead iodides (CnH2n+1NH3)2PbI4, n = 12, 16, 18, display two phase transitions, just above room temperature, associated with changes in the alkylammonium chains. We have followed these two phase transitions using scanning calorimetry, X-ray powder diffraction, and IR and Raman spectroscopies. We find the first phase transition to be associated with symmetry changes arising from a dynamic rotational disordering of the ammonium headgroup of the chain whereas the second transition, the melting of the chains in two dimensions, is characterized by an increased conformational disorder of the methylene units of the alkyl chains. We examine these phase transitions in light of the interesting optical properties of these materials, as well as the relevance of these systems as models for phase transitions in lipid bilayers.
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