Thermoelectric properties of La/sub 2-x/SrxCuO4

La/sub 2-x/Sr/sub x/CuO/sub 4/ is unique among the high T/sub c/ superconductors with high values of Seebeck coefficient in the normal state for x<0.1, in addition to a low thermal conductivity. Seebeck coefficient and electrical conductivity were measured for samples of sintered and single crystal La/sub 1.95/Sr/sub 0.05/CuO/sub 4/ in order to look for the optimum concentration of Sr as related to its thermoelectric properties at room temperature. At this doping level this material is in the region of metal-insulator transition. Room temperature values of 147 /spl mu/V/K and 0.01 /spl Omega/cm for the Seebeck coefficient and the electrical resistivity, respectively, were obtained for a sintered sample. For a single crystal of the same composition, the Seebeck coefficient parallel to the ab planes is 143 /spl mu/V/K and along the c axis it is 156 /spl mu/V/K. The electrical resistivity was measured only along the ab planes, down to about 9 K. The R.T. value was 0.03 /spl Omega/cm. No significant change was observed after annealing, either in oxygen or in vacuum. There is a significantly different behavior of the temperature dependence of the resistivity between the sintered and single crystal samples: the sintered sample has a metallic behavior from room temperature down to 80 K, and there is no superconducting transition above 10 K-whereas the single crystal shows semiconducting behavior from R.T. down to the superconducting transition with an onset temperature of 17 K (along the lower resistivity ab planes). Our data are compared with published data of different values of x in the system La/sub 2-x/Sr/sub x/CuO/sub 4/.