High temperature thermodynamic properties, orthorhombicrtetragonal transition and phase stability of GdBa Cu O and related R123 compounds

F. PRADO; A. SERQUIS; A. CANEIRO

PHYSICA C - SUPERCONDUTIVITY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1998 vol. 295 p. 235 - 246

0921-4534

Thermogravimetric measurements of the equilibrium oxygen partial pressure pO2.. as a function of temperature andoxygen content have been made on GdBa2Cu3Oy Gd123. within the range 3=10y4 atmFpO2 .F1 atm and 4508CFTF8008C. The partial molar entropy DSO2. and enthalpy DHO2. of solution of oxygen in Gd123 are evaluated anddiscussed. The pO2. data on Gd123 are compared with measurements performed on NdBa2Cu3Oy Nd123. at 8008C andliterature data for YBa2Cu3Oy Y123. at 6008C and 8008C. The orthorhombicrtetragonal transition temperature TOrT . forGd123 and Nd123 as a function of the oxygen partial pressure 1=10y3 atmFpO2.F1 atm. has been determined byhigh temperature X-ray diffraction HTXRD.. The oxygen content values for the OrT transition yOrT . at several pO2 .values for Gd123 and Nd123 have been determined by means of thermogravimetric measurements. The obtained data in they–T diagram supports the applicability of the quasichemical approximation in describing the OrT transition of Gd123 andNd123 compounds. The effect of the R atom RsY, Gd, Nd. ionic size on the oxygen stoichiometry and phase stability ofR123 compounds at high temperature is discussed, and a possible explanation is proposed which accounts for the latticemismatch between Ba–O and CuO2 layers.