Observation of variable-range hopping up to 900 K in the YLaxBa2-xCu3O7- system

Semiconducting phases in the system YLaxBa2-xCu3O7- (x=1.0-0.0) exhibit three-dimensional variable-range hopping conduction over a wide temperature (T) range (100-900 K). Thermopower (S) measurements support this observation. S increases with T for x=1.0 and 0.8 indicative of transport at the chemical potential E. The decrease in S with T for x=0.4 and 0.3 is indicative of gap at E. A schematic band picture is used to explain the observed behaviors. © 1995 The American Physical Society.