The ( = 0, 0.025, 0.05, 0.075, 0.1, 0.15, 0.2, 0.3, 0.4 and 0.5) nanopowders were synthesized by the hydrothermal method and then were hot-pressed into bulk alloys. The effects of secondary phase on the thermoelectric (TE) properties of were investigated. For and , both their electrical resistivity and Seebeck coefficients increase. While for , they decrease instead. The samples for have lower thermal conductivity. However, for , the thermal conductivity rises remarkably. As an overall result, the maximum value of dimensionless TE figure of merit ( ZT) reaches 1.52 at 873 K for the sample of , 36.5% higher than for the sample without . [ABSTRACT FROM AUTHOR]