Thermoelectric properties and phase stability of La/sub 10/S/sub 14/O

The electrical resistivity, thermopower, thermal conductivity measurements have been made on tetragonal La/sub 10/S/sub 14/O. The electrical resistivity was measured during heating and successive cooling through 300 and 1000 K to investigate the high-temperature phase stability. The measurements were carried out in the vacuum chamber pumped down to 1.0 Pa. The electrical properties of La/sub 10/S/sub 14/O are changed dramatically through heat treatment. As annealing time increases, the electrical resistivity increases abruptly and then decreases gradually. However, it seems that this phase can be stabilized by a small addition of Ti. In the electrical resistivity of La/sub 10/S/sub 14/O with Ti, the cooling curve agrees with heating curve. Moreover, the ZT value increases abruptly with increasing temperature, reaching a value of 0.18 at 1000 K. The improvement with respect to the thermoelectric properties of the La/sub 10/S/sub 14/O is realized by a small addition of Ti.