Enhanced thermoelectric properties of bulk TiNiSn via formation of a TiNi2Sn second phase

The effect of phase-segregated Heusler TiNi2Sn on high temperature thermoelectric properties of bulk half-Heusler TiNiSn has been studied. In samples expressed by the composition TiNi1+xSn, a significant decrease in thermal conductivity (between 10% and 30%) is observed for two-phase TiNi1.15Sn, despite the second-phase particles existing at the micrometer scale; a 50% increase in the electrical conductivity is also measured. These result in a maximum figure of merit, ZT, of 0.44 at 800 K, which is 25% greater than is observed for the x = 0 sample. Density functional calculations of TiNiSn and TiNi2Sn suggest that the latter should deplete carriers at OK.