Ryuji Sakamoto

Thermoanalytical investigation of the (YBa22Cu6Oy superconductor. I. reactions forming the superconductor and its phase changes

Abstract Thermogravimetry (TG)-differential thermal analysis (DTA) and high-temperature microscopy studies of oxalates of yttrium, barium and copper have been made to investigate the formation processes of the (YBa 2 Cu 6 O y superconductor. TG, DTA and high-temperature X-ray diffractometry were also used to observe phase changes of the superconductor. The final process in the formation of the superconductor has been elucidated and a phase transition accompanied by oxygen sorption was observed in addition to fusion. The equilibrium content of the oxygen sorption was measured by isothermal TG.

Thermoanalytical investigation of (YBa2)2Cu3O7-y superconductor: II. perovskite formation from coprecipitated oxalate

Abstract Formation of the perovskite structure from the precursor was observed by high-temperature X-ray diffractometry. It proceeds in the temperature range above 750° C. Thermogravimetry (TG)/differential thermal analysis (DTA) was also applied to this temperature range: weight loss and an endothermic peak were observed in a higher temperature range. The endothermic peak is due only to a phase change of BaCO 3 in the precursor and is independent of the weight loss, which is due to evolution of CO 2 from BaCO 3 when perovskite formation proceeds. Kinetic analysis of these processes showed that the weight loss is a phase-boundary-controlling process.

Thermoanalytical investigation of YBa2Cu3O7−y superconductor: III. Preparation from mixed 2-ethylhexanoates of yttrium, barium and copper

Abstract The preparation of YBa 2 Cu 3 O 7− y from mixtures of the 2-ethyl-hexanoates of yttrium, barium and copper has been investigated by thermogravimetry (TG), TG-DTA (differential thermal analysis). X-ray diffractometry, and energy dispersion X-ray analysis (EDX). The mixture is first transformed to a mixture of BaCO 3 , Y 2 O 3 and CuO below 500°C and then the perovskite formation proceeds. Kinetic analysis of TG data on the perovskite formation has been performed.

Thermoanalytical investigation of YBa2Cu3O7-y superconductor. IV. Mechanism of perovskite formation from various starting materials

Abstract Thermogravimetry (TG) at various heating rates was applied to perovskite formations of YBa 2 Cu 3 O 7- y prepared from coprecipitated carbonates of yttrium, barium and copper, and from a physical mixture of yttrium oxide, barium carbonate and copper oxide. Kinetic analyses of TG data were made for the two starting materials. Mechanisms of perovskite formation are discussed in comparison with other starting materials: mixed 2-ethylhexanoates and coprecipitated oxalate.