Large transverse Seebeck voltage in oxygen-reduced YBa/sub 2/Cu/sub 3/O/sub 7/ and Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

摘要

The off-diagonal Seebeck voltage of oxygen-reduced YBa/sub 2/Cu/sub 3/O/sub 7/ and Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films epitaxially grown on strontium titanate crystals cut with a tilt angle of 20/spl deg/ between substrate surface and the cubic axis was measured. A temperature gradient perpendicular to the film surface was produced at room temperature by exposing the films to UV radiation pulses. The transverse Seebeck voltage, i.e. the voltage parallel to the film surface, which results from the temperature gradient perpendicular to it, was measured for varying oxygen content and Pr doping of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films. The oxygen content of the YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films was reduced from /spl delta//spl sime/0 to /spl delta//spl sime/0.5. It is shown that a reduction of the oxygen content causes a decrease of the off-diagonal Seebeck voltage. The same effect is observed for the Y/sub 1-x/Pr/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta//(x= 0.1, 0.2, 0.3) thin films, i.e. raising the partial substitution of Y by Pr results in a smaller Seebeck voltage. These results suggest that both, oxygen reduction and Pr doping, have the effect of making YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// less anisotropic with respect to the thermopower. On the other hand, results of resistivity measurements of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// with different values of /spl delta/ suggest that the anisotropy increases when oxygen is removed. A microscopic model for an explanation of the different behaviours of the thermopower and the resistivity is still lacking. We also have measured the transverse Seebeck voltage of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//(/spl delta//spl sime/0.06 and 0.19) from T/sub c/ to room temperature. From this we can conclude that S/sub e/ of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (/spl delta//spl sime/0.06 and 0.19) increases linearly with temperature, i.e. S/sub c/ shows metallic behaviour.