Structure and phase transitions in guanidinium halogenobismuthates(III)

Abstract Differential scanning calorimetry (DSC), dilatometric and dielectric measurements have been used to study the phase transitions in [C(NH2)3]3BiBr6. The [C(NH2)3]3BiBr6 crystal undergoes four phase transitions: at 419, 429, 475 and 495 K (on heating). The high-temperature phase transition is clearly of first-order type and its high entropy effect allows classifying it as of the order–disorder type. X-ray diffraction studies showed that [C(NH2)3]3BiBr6 crystallises in monoclinic, centrosymmetric space group, C2/c. The anionic sublattice is composed of isolated BiBr63− octahedra. The infrared between 100 and 350 K and Raman spectra at room temperature in the frequency range related to…