Stabilization and Thermoelectric Properties of Rare Earth Chalcogenides γ-LaSy

Abstract

Phase relation and thermoelectric properties of LaS_y. (4/35≤y≤93/2) were examined. Three phases (β, γ and LaS) were obtained by the direct reaction of La and S in an evacuated quartz capsule at 1000-C. Single phase 7 -LaS_y, which has Th₃P₄-type structure, was obtained by reaction sintering at 1600-C in a vacuum in the range of 1.33≤y≤51.39.γ-phase easily transforms to 8-phase and the strong reduced atmosphere is necessary for the stabilization of 7-phase. The electrical resistivity (r) and thermoelectric power (a) of 7 -LaS, increase with an increase of sulphur content y. Power factor (α²/r) of LaS_1.39 larger than that of laS_1.33.