Charactarization of High-Temperature Superconducting Oxides by thermogravimetry.

Abstract

Oxygen deficiency of Y-Ba-Cu-O was determined by in situ observation of weight loss in hydrogen atmosphere with thermogravimetry (TG). Oxygen stoichiometry for various phases was found to be as follows: orthorhombic phase (YBa_2Cu_3O_7.0), tetragonal phase (YBa_2Cu_3O_6.23) quenched at liquid nitrogen temperature from 930℃, tetragonal phase with charactor of insulator (YBa_2Cu_3O_6.0) quenched at 645℃ in vacuum (10^-4 mmHg). Amount of oxygen defects of YBa_2Cu<3_χ>Co_χO<7-δ> increases with increasing Co-contents whereas T_c decreases, indicating the valence of Co-ion above 3. Phase transition temperature depends on partial oxygen pressure.