Synthesis, structures and bonding of superconducting barium vanadium suflide and intermetallic solid state compounds of group 2, 3, 13, 14 and transition elements.

摘要

Superconducting transition is well known for the Chevrel phases M _xMo₆S₈ and M_xMo₆Se ₈ where M is dopant metal such as Pb, In, Tl and La. Not many ternary group 5 transition metal chalcogenides of similar composition, however, are known to be superconductors. The synthesis and observation of superconducting transition of the Ba doped compound Ba_xV₆S₈ (x = 0.45–0.48) is discussed. The electronic structure was analyzed using the tight-binding extended Hückel method. Results of Raman-scattering experiments are also discussed.; BaGa₄ possesses the most popular structure type in solid state chemistry. More than 600 compounds crystallize in this structure. Many compounds of this family exhibit interesting physical properties such as superconductivity, unusual magnetic behavior, valence fluctuation and heavy fermion phenomena. However, little had been reported about the physical properties of BaGa ₄ itself. The single crystal growth, structural characterization, computational his, conductivity and AC susceptibility of crystalline BaGa₄ is described.; V-Ga binary system is of great interest because some compounds in this family are superconductors exhibiting high critical currents and fields. V ₂Ga₅ has been reported to show a superconducting transition from 2.1 K to 4.2 K,2,6 depending on the preparation procedure and sample quality. However, no single-crystal X-ray structure determination has been reported for this compound, and the full characterization of its superconducting transition has yet to be completed. The single crystal growth, structural determination, and computational study of Ga₅V ₂ are discussed. Resistivity and magnetization measurement results are also presented.; Ternary intermetallic solid-state compounds of lanthanum, transition metal, and germanium have a wide range of technological applications (i.e., rechargeable cells) because of their interesting physical properties. Many compounds of this type with the stoichiometry Ln_xT_yGe _z (Ln = lanthanide, T = transition metal) have been synthesized. A few of them crystallize in orthorhombic lattices in which a transition metal forms a square lattice with capping germanium atoms on the square hollows. This structural motif is found in one of the most populous families, the ThCr ₂Si₂ series that has more than 600 members. LaNiGe₂ , is similar in structure with capped square nets. However, there is one very important difference. In this structure, it is the more electronegative element Ge that builds the square lattice. The main structural motif is the NiGe₄ pyramid. With computational analysis as the means of exploration, the electronic charge distribution resulting from such a structural arrangement and the changes that occur to this electronic charge distribution when a partial substitution of Si is made to the Ge in the square lattice are described. Two partially substituted compounds with different levels of Si substitution were synthesized. Their synthesis and magnetic susceptibility measurements are also discussed.