THERMAL EFFUSION MASS SPECTROSCOPIC CHARACTERIZATION OF BULK YBA2CU3O(7-DELTA) IN COMPARISON TO CUO, BAO, BACO3 AND Y2O3

Thermal effusion from bulk samples of superconductor YBa2Cu3O7-delta i s examined by monitoring of all desorbing species via quadrupole mass spectrometry; For comparison purposes, thermal decomposition of the si mple BaO, BaCO3, CuO and Y2O3 is also investigated. In these salts, ef fusion activation energies for oxygen and CO2 are shown to relate to t he thermodynamics of the decomposition reactions leading to the evolut ion of these species in the gas phase. On the other hand, the activati on energies of effusion for the metallic species reflect their binding in the distorted crystal left behind after oxygen or CO2 ejection. In the case of the superconducting YBa2Cu3O7-delta the activation energy of effusion is found to be negligibly (barium species) or little affe cted (copper) when comparing YBa2Cu3O7-delta with the simple salts. In contrast, the activation energy of effusion of YO shows a large effec t, being almost a third-of that determined for Y2O3. The difference su ggests that the final residue left by the thermal decomposition of YBa 2Cu3O7-delta must be a highly disrupted Y2O3(s) structure, with signif icantly different thermodynamic properties. (C) 1997 Elsevier Science B.V.