Materials Science and Chemistry

Biography

Biography: Mihai I Sturza

Abstract

The class of transition-metal chalcogenides that exhibits mixed valency has been of continuing interest for several decades. The emergence of superconductivity with a superconducting transition temperature (Tc<30 K) in mixed-valence AxFe₂−ySe₂ (A=K, Rb, Cs, and Tl) phases has further increased interest in the chemistry and physics of complex ternary transition-metal chalcogenides. Copper chalcogenide materials are of considerable scientific interest because of their rich structural and compositional diversity, mixed valency, propensity for phase transitions, charge-density waves, potential for ionic mobility, as well as applications such as high performance photovoltaic cells. New results from the chemistry of the A/Cu/Q (A=Na, K, Ba; Q=S, Se) system will be reported. The synthesis, crystal structure, and properties of new layered copper chalcogenide compounds, which are mixed-valent will be presented. Single crystals were grown by the reaction of Cu metal in a molten alkali/ alkaline-earth metal/polysulfide/polyselenide/flux. Single crystal x-ray diffraction measurements performed on several crystals showed a high quality of the crystals, proven by the good internal consistency of the data collected using the full-sphere mode and an extremely low R factor. Electronic band structure calculations and physical property measurements reveal p-type metallic behavior, with moderately high electrical conductivity and hole carrier mobilities.

Crystal structure, SEM image and conductivity measurement of NaBa₂Cu₃S₅ crystal, a novel mixed-valent transition metal chalcogenide discovered by polychalcogenide flux synthesis