PREPARATION OF PURE TL2BA2CUO6+/-X - THE CONTRIBUTION OF PHASE-EQUILIBRIUM STUDIES

The formation of the pure thallium-based cuprate Tl2Ba2CuO6+/-x (2201 ) using a convenient process in the ternary TlO1.5-BaO-CuO phase diagram is described. This process is based on the congruent formation of the oxide Tl2Ba2O5 to which CuO is mixed, constituting a quasi-binary system. In the resulting 2201 compound no trace of the main poisoning magnetic impurity BaCuO2 could be detected by AC susceptibility measurements. The orthorhombic to tetragonal transformation is asserted to be due to thallium deficiency which occurs during the heat treatments at a temperature depending on the oxygen partial pressure.