Influence of phase on thermoelectric properties in lanthanum sesquisulfide doped with titanium

The thermoelectric power and the electrical resistivity in lanthanum sesquisulfide (La₂S₃) doped with Ti at 300 K were measured over the dopant Ti content ranging from 0.5 wt %. to 15 wt %. The tetragonal (β) phase powder which contains impurity oxygen of about 5 atomic % was used as, the starting material. The samples, were prepared by vacuum hot-pressing at the temperature range from 1323 K to 1773 K for 3.6 ks. The phase of the compacts obtained changes with the amount of the dopant Ti content and the sintered temperature from the β phase to the cubic (γ) phase. Moreover, the LaS phase is formed at the initial stage in the phase change. The absolute value of the thermoelectric power and the electrical resistivity decrease with the phase change. The compacts which are mainly composed of the γ phase exhibit a large power factor.