Author :
Ono, Yasuhiro ; Inayama, Shingo ; Adachi, Hideaki ; Kajitani, Tsuyoshi
Abstract :
Thermoelectric properties of doped half-Heuslers, NbCoSn1-x Sbx and Nb0.99Ti0.01CoSn1-x Sbx, have been studied in the temperature range from 320 K to 850 K. These half-Heuslers were synthesized by the arc-melting of pure metals followed by annealing for one week at 1123 K in vacuum. The samples with x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10 are prepared by the spark plasma sintering, SPS, method using fine powders of the crushed arc-melted buttons. Sintered samples are of nearly single phase. All the samples exhibit metal-like temperature dependent rho of the order of 10-6-10-5 Omega-m in the measured temperature range. In both NbCoSn1-xSbx and Nb0.99Ti0.01CoSn1-xSbx, the rho values at 320 K rapidly decrease by the partial substitution in the range between x = 0 and 0.02, and finally reach 5 muOmegamiddotm at x = 0.10. Seebeck coefficient, S, is appreciably enhanced by partly substituting the Nb site with 1 at.% of Ti. The highest power factor is 22 times 10-4 Wmiddotm-1 middotK-2 for Nb0.99Ti0.01CoSn 0.9Sb0.1 at 700 K. The thermal conductivity, kappa, weakly depends on temperature and does not show any peculiar trend due to Sb partial substitution. Dimensionless figure of merit, ZT = S2T/rhokappa, for Nb0.99Ti0.01CoSn0.9Sb0.1 reaches 0.3 at 850 K, which is four times higher than that of the pure NbCoSn
Keywords :
annealing; cobalt alloys; melting; niobium alloys; semiconductor materials; sintering; thermal conductivity; thermoelectricity; titanium alloys; 1123 K; 320 to 850 K; Nb0.99Ti0.01CoSn0.9Sb0.1 ; NbCoSn; crushed arc-melting; dimensionless figure of merit; doped half-Heuslers; partial substitution; power factor; spark plasma sintering; thermal conductivity; thermoelectric properties; vacuum annealing; Annealing; Niobium; Plasma measurements; Plasma temperature; Temperature dependence; Temperature distribution; Temperature measurement; Thermal conductivity; Thermoelectricity; Vacuum arcs;
