Anomalous behaviour of thermal conductivity of Tl-Ba-Ca-Cu-O

The thermal conductivity of the Tl-Ba-Ca-Cu-O compound with nominal composition 2-2-2-3 has been investigated in the temperature range 4.2–300 K. An anomalous behaviour was observed near and above the superconducting transition. Time dependent effects were found below T c. They are ascribed to the migration of nonstoichiometric oxygen. An increase of the thermal conductivity at a temperature of about 155 K was attributed to some phase transition rather than the beginning of the superconductivity. The anomaly at about 225 K might be connected with the oxygen vacancy ordering.