IMF2017

A family of the cyano-bridged coordination polymers (CPs), which undergo a phase transition between high and low dielectric states upon thermal stimulus, are promising materials for potential application in electrical and electronics devices. The inorganic cage compounds, with the organic guest molecules as cations, may give materials, where solid-to-solid phase transitions with different nature like order-disorder or displacive-type can be observed. The carefully designed guest/host materials, where into well-matched host framework the switchable guest is placed, leads to crystals with interesting physicochemical properties, i.e. the large dielectric/magnetic susceptibility, spontaneous polarization and/or non-linear optical ones. We would like to present the dielectric, optical and thermal properties of the novel crystals, which are classified as an elpasolite family. These materials have a double perovskite-type structure, ones the cage framework is formed (with the general formula: A’₄A”₄(CN)₁₂, A’-monovalent metal, K⁺, and A”-trivalent metal, Fe³⁺/Co³⁺) the cationic organic guest are embedded in the cage. We would like to prove that the mechanism of the phase transition is related both to a change in dynamics of cations and a deformation of the inorganic structure. It is worth to highlight that in our work not only the cationic/guest but also anionic/host-framework dynamics has been described and the appropriate models of the molecular disorder are proposed. The detailed analysis of the structural properties allows us to describe a correlation between the microscopic structure and the dielectric and optical properties of the crystals.