Phase equilibria in the thallium superconducting system will be measured. The goal is to understand the complex solid-liquid- vapor equilibria that govern crystal growth of the thallium based family of superconductors. This study will involve exposure of films and powder mixtures of known composition to controlled overpressures of thallous oxide and oxygen vapor at high temperature (600 - 950 C) followed by quenching. The composition and microstructure of quenched samples will be examined to identify the equilibrium high temperature phases. In this manner the liquidus and solidus temperatures, equilibrium overpressures, and stable phases will be determined in those regions of composition that are important for thin film and crystal growth. Additional information on phase changes will be gained by differential thermal analysis (DTA) using sealed gold ampoules to control thallium volatility.
