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

Abstract

Semiconducting phases in the system YLa{sub {ital x}}Ba{sub 2{minus}{ital x}}Cu{sub 3}O{sub 7{minus}{delta}} ({ital x}=1.0--0.0) exhibit three-dimensional variable-range hopping conduction over a wide temperature ({ital T}) range (100--900 K). Thermopower ({ital S}) measurements support this observation. {ital S} increases with {ital T} for {ital x}=1.0 and 0.8 indicative of transport at the chemical potential {ital E}{sub {mu}}. The decrease in {ital S} with {ital T} for {ital x}=0.4 and 0.3 is indicative of gap at {ital E}{sub {mu}}. A schematic band picture is used to explain the observed behaviors.