Exploratory synthesis in molten salts: Characterization, nonlinear optical and phase-change properties of new chalcophosphate compounds

The polychalcophosphate flux technique has played an important role in discovery of new chalcophosphate compounds via access to low and intermediate temperature of 160--600°C. Chalcophosphates are compounds that possess phosphorus and chalcogen atoms with P-Q bond, where Q = S, Se, or Te. The structural diversity within the class of metal chalcophosphates is extensive, and members of this family can exhibit technologically important ion-exchange, intercalation, magnetic, electrical, and optical properties.;In the present work exploratory synthesis of chalcophosphate compounds using polychalcophosphate molten salt method and characterization of physicochemical properties that are mainly concentrate upon nonlinear optical properties and crystal-glass phase-change behavior are described. Chapters 2-6 focus on the effort of systematic study of alkali metal selenophosphate ternary compounds. The first family of this class is one-dimensional compounds, APSe6 (A = K, Rb, Cs) and A2P2Se6 (A =K, Rb). The compounds adopt noncentrosymmetric polar space group and exhibited remarkably strong second harmonic generation response in both crystalline and glassy phases. They also show a reversible crystal-glass phase-change behavior. By coupling noncentrosymmetry in crystal structure and phase-change behavior, we proposed general fabrication strategy for optical glassy fibers that yield strong, intrinsic, second-order nonlinear optical properties. The APSe 6 (A=K, Rb) glassy optical fiber exhibited waveguided second harmonic and difference frequency generation. The second family of this class is phosphorus-rich, novel molecular complex salts of Rb4P6Se12, Cs4P6Se12, and Cs5P5Se 12. All compounds feature low valent P in two different formal oxidation states. We attempted rational synthetic conditions to stabilize less oxidized phosphorus compounds by utilizing excess P in the flux. The polychalcophosphate flux also produced rare phosphorus telluride compound. The new compound K 4P8Te4 featuring P-Te bonding exhibited reversible crystal-glass phase-change behavior, dissolution process to photoluminescent solution with hydrazine, and evolution of nanosphere by precipitating the resulting solution with alcohol. Finally stabilizing Bi metal with selenophosphate flux at high temperature gave naturally growing flexible nanowires of Cs 5BiP4Se12 that can be dispersed in alcohol. The compound that adopts the noncentrosymmetric polar space group exhibited strong near-IR second harmonic generation response.