This is a proposal to study the structure of bulk and thin film oxide superconductors using perturbed angular correlation (PAC) spectroscopy. The primary objectives of the proposed research are: to determine the site-occupation probabilities of indium in Yttrium-Barium-Copper-Oxide material as a function of temperature, oxygen concentration, and cation-alloy composition; to determine the nature of the orthorombic/tetragonal phase transition which occurs near 700C; and to provide accurate information about the Yttrium-Barrium-Copper-Oxide phase diagram at high temperatures. Other major objectives are: to study oxygen defect trapping by indium at low temperatures; and to study oxygen ordered phases at low temperature. These issues are important for the processing of high Tc superconductors.
