Equilibrium diagram Tc(T;p(O2)) of Tl2Ba2CuO6

Homogeneous Tl 2 Ba 2 CuO x ceramics were synthesized by a novel route allowing tight control of thallium losses, starting from Tl 2 Ba 2 O 5 precursors and using high gas pressures. Annealing followed by fast quenching into gallium allowed us to map the critical temperature (0 to 92 K) and the crystal symmetry (orthorhombic or tetragonal) in the (T;p(O 2 )) plane. The orthorhombic phase is found to be stoichiometric, whereas the tetragonal phase has a homogeneity domain in the thallium concentration. The critical temperature, determined by the oxygen concentration, is not sensitive to the crystal structure. Selected physical properties of Tl 2 Ba 2 CuO x compounds are presented.