Klymenko N. Structure and phase transitions in molecular crystals of methane and ethane groups

The thesis combines results of studies of structural and thermodynamic properties and phase transitions of tetrafluoromethane CF4, silane SiH4, ethane C2H6, and hexafluoroethane C2F6. The structures of several phases are obtained for the first time. The lattice parameters and volumes were reliably determined and their temperature dependence were built. The temperature dependence of linear and volumetric thermal expansion coefficients is first obtained for the substances investigated. It allows to identify all temperature dependences of the heat capacity of the matters at constant volume CV. The analysis of the contributions to heat capacity of the various subsystems is conducted. Temperature dependence of the Gruneisen coefficient is built. Due to the comparative analysis of the structural characteristics for crystals of methane and ethane series, the conclusion about the isostructurality of high-temperature monoclinic phases of silane, tetrafluoromethane, and monoclinic low-temperature phases of tetrachloro- and tetrabrommetane is made.