Electrical properties of yttrium sesquisulfide (Y2S3) mechanically alloyed with copper, boron, and aluminum

Abstract

The electrical resistivity, thermoelectric power (Seebeck coefficient) and Hall effects have been measured for (Y2S3)1−xX3 compounds with the δ-monoclinic structure (where X = Cu. B or Al and y = 0.05 for Cu and B, and 0.025 ≤ y ≤ 0.075 for Al) in order to determine their potential as high temperature (300–1000°C) thermoelectric materials. The Cu- and B-doped Y2S3 are insulators. The Al-doped Y2S3 behaves as a metastable degenerate semiconductor with itinerant conduction. The room temperature electrical resistivity decreases as the Al doping level increases, while the Seebeck coefficient remains constants at ca.400 μV eC1. These materials, however, become insulators after a 2 week heat treatment at 1000°C or higher. Both the electrical resistivity and Seebeck coefficient increased with increasing temperature, and exhibited lower values during the cool down run to room temperature. These data suggest that the (Y2S3)1, Al, alloys are in a metastable state in which the Al atoms occupy the interstitial sites of the Y2S3 lattice, where it acts as a current carrier donor. When heated, the Al atoms diffuse out of the lattice and no longer contribute to the electrical conductivity, thus making the alloy an insulator. The maximum value of the power factor was 0.6 μW cm 1 °C 2, and decreased with increasing temperature. The results of this study indicate that Cu-, B-, and Al-doped Y2S3 are not useful as high temperature thermoelectric materials.