Thermoelectric power of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

Results of thermoelectric power (TEP) measurements of the high-temperature superconductor ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ as a function of oxygen content are reported here. Removal of oxygen produces two distinct changes in TEP versus temperature curves: (1) It raises the TEP curves, and (2) it raises the temperature at which the slope of the curves changes from positive to negative. These changes result from (1) the decrease in the charge carrier density and (2) lattice distortions; both are due to increasing oxygen vacancy. Results of measurements on strontium-substituted compounds show only the second type of change in the TEP versus temperature curves.