The influence of the technological parameters of its synthesis on the superconducting and structural properties of PbMo6S8 has been investigated. For the first time lattice instability near 80 °K has been detected from x-ray structural studies carried out on PbMo6S8 in the temperature range 4.2–300 °K. The resistivity ρ(Tc − 300 °K), magnetic susceptibility χ(Tc − 300 °K), and specific heat Cp (2–300 °K) of the PbMo6S8 system were measured as a function of the temperature. Joint analysis of the experimental results and the data in the literature on inelastic neutron scattering at 4.2 and 300 °K enabled us to make the first quantitative calculations of the phonon specific heat and its anharmonic component, the temperature dependence of the electronic specific heat coefficient γH(T), the band density of electronic states at the Fermi level NBS(EF), and the electron-phonon interaction constant λ(T). It has been found that the ρ(T), γH(T) and λ(T) curves display anomalies near temperatures ≈80°K, at which lattice instability occurs, and the high-field superconductivity in PbMo6S8 is a consequence of the large value of NBS(EF).

Measurements have been made on the temperature dependence of the specific heat, relaxation time, and NQR frequency for Bi12GeO20 and Bi12SiO20 crystals over the range 4.3-300°K; there are low-temperature anomalies in T1(T) and T2(T). These features are not related to phase transitions and are due to defects of different kinds.