Detrimental effects of impurity phases on the thermoelectric performance of Nb_0.8Ti_0.2Fe_1.02Sb synthesized by arc-melting

We demonstrate the detrimental impacts of impurity phases on thermoelectric (TE) performance in Nb_0.8Ti_0.2Fe_1.02Sb system that instigate performance irreproducibility that may impede rapid and progressive performance improvement of compounds synthesized by arc-melting. Three samples prepared by arc-melting are annealed at 700 °C, 850 °C and 1000 °C. The optimal homogeneity is achieved in the sample annealed at 850 °C with ~0.8% impurity phases’ quantity, relative to ~4% and ~10% in the samples annealed at 700 °C and 1000 °C, respectively. The samples with increased impurities depict a significantly decreased Seebeck coefficient and increased lattice thermal conductivity, which intimately impairs the TE performance. The highest ZT is achieved in the sample with the least impurities, ~0.73 at 873 K, which is 49% higher than the inhomogeneous samples. This stresses the pertinence of minimizing the impurities in a bid to reproduce the optimal TE performance from this system.