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Order‐Disorder Phase Transition, Anisotropic and Switchable Dielectric Constants Induced by Freeze of the Wheel‐Like Motion in a Hexafluorosilicate‐Based Crystal
Author(s) -
Liu Sijie,
Li Jun,
Sun Zhihua,
Ji Chengmin,
Li Lina,
Zhao Sangen,
Luo Junhua
Publication year - 2016
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201601263
Subject(s) - orthorhombic crystal system , monoclinic crystal system , phase transition , condensed matter physics , dielectric , materials science , anisotropy , phase (matter) , crystallography , crystal (programming language) , chemistry , crystal structure , physics , optics , organic chemistry , programming language , optoelectronics , computer science
An order‐disorder phase transition is found in a hexafluorosilicate‐based crystal, bis(betainium) hexafluorosilicate bis(betaine) ( 1 ). At room temperature, 1 crystallizes in an orthorhombic space group Fddd and the hexafluorosilicate moiety exhibits partial disorder which originates from a uniaxial wheel‐like rotation. As temperature decreases, a total freeze of this wheel‐like motion results in a second‐order phase transition at 250 K and the low temperature phase of 1 belongs to a monoclinic space group C /2 c . Thermal measurements and variable‐temperature single‐crystal X‐ray diffractions confirm that distinctive order‐disorder transformation of the anionic rotor is the main driving force for the solid‐state phase transition. Further, theoretical computation of potential energies for the wheel‐like motion elucidates the dynamic changes in the anion from rotating to static state. Moreover, dynamic changes of the crystalline in‐plane rotor give rise to anisotropic and switchable dielectric constants.