Synthesis, electrical and superconducting Chevrel phases containing oxygen

Chevrel phases of the type Asub(x)Mosub(6)Ssub(8), - Sesub(8) (A=metal) are superconductors with high Tsub(c) and Hsub(c). It is possible to obtain a large variety of new materials with interesting physical properties by substitution at the A, Mo and Ch sites in the system. It has been possible to prepare compounds in which O-atoms are partially substituted at the S Site, viz., Asub(x)Mosub(6)Ssub(8-y)Osub(y) with y <= 2 and A=Cu2, Ni2, Pb. The compounds were synthesized by high temperature solid state reactions and were characterized by X-ray and density measurements. Electrical resistivity (rho) and Tsub(c) measurements of sintered pellets were performed (range 4.2-300K). Seebeck coefficients (α) were measured in the range 77-300K. rho-T and α-T behavior of O-containing phases are similar to -Ssub(8) phases. However, subtle properties like crystallographic transition temperature (Tsub(t) in Cu2Mo6S8) and Tsub(c) which are dependent on the details of band structure and electron phonon interaction (coupling) are nontrivially altered by O-substitution. (author)