Spectral investigation of the phase-transition behavior in (DOEO)4HgBr4·TCE salt

Room temperature electrical conductivity of (DOEO)4HgBr4·TCE single crystals measured along the a-direction is of the order of 1 S/cm, while perpendicularly to this direction is almost five orders of magnitude smaller. Besides, on cooling the resistivity increases until a maximum reached around 140 K, becomes metallic in the lower temperature, and finally undergoes an insulating transition around 50 K. To add some new observations and explain these interesting properties of the salt we present extended investigations of its spectral properties. In this paper, we discuss the temperature EPR studies of (DOEO)4HgBr4·TCE salt as well as the evolution of its IR spectra vs. temperature. In particular, the analysis of changes of selected normal modes wavenumbers is discussed. Significant changes of EPR shape and characteristic line splitting were observed. It was shown that possible explanation for the peculiar resistivity of (DOEO)4HgBr4·TCE salt observed at about 140 K relates to the disordering of anions and ethylene groups. Their partial ordering can lead to the observed metallic behavior but cannot prevent further localization at lower temperature.

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► We examine changes in the temperature evolution of normal modes in IR spectra.
► The electron paramagnetic resonance (EPR) spectra have been presented and discussed.
► An explanation of a peculiar resistivity behavior observed at 140 K has been given.
► EPR data show that below 140 K the [HgBr4]2− anions are ordered.
► The partial ordering of anions and ethylene groups lead to the metal conductivity.