The influence of sample geometry on measured physical properties (the magneto-Seebeck effect, Nernst effect, magnetoresistance effect, Hall effect, and thermal conductivity) in a magnetic field was investigated for a polycrystalline Bi-Sb sample. The polycrystalline Bi₈₈Sb₁₂ bulk sample was prepared using the spark plasma sintering method and annealing, and the physical properties obtained via measurements in magnetic fields of 5 T were compared with the simulated values obtained by the finite element method with considering various sample geometries. The appropriate shape required for the precise measurement of less than 2% error was found to be different for each physical property: the required aspect ratio of length l to width w is l/w > 0.57 for the magnetoresistance effect, l/w > 2.9 for the Hall effect, l/w > 4.2 for the two-wire magneto-Seebeck effect, l/w > 1.2 for the four-wire magneto-Seebeck effect, and l/w > 3.1 for the Nernst effect. We also found that a small error of less than 2% in the thermal conductivity measurement requires K_s/K_w > 27, where K_s and K_w represent the thermal conductance of sample and that of lead wire, respectively.

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The thermoelectric properties of TiNiSn_1-xSb_x (0 ≤ x ≤ 0.05) prepared by arc melting are measured up to 800 K to obtain ZT. Hall effect measurements and ab initio calculation using AkaiKKR are performed to confirm the Sb substitution effect. The density of states before and after substitution show that Sb acts as a donor. Thermoelectric properties show that the absolute values of the electrical resistivity and Seebeck coefficient decreased with increasing x while the thermal conductivity increased. This is consistent with the carrier density-dependent trends when the carrier density increases. Hall effect measurements at room temperature also show that the carrier density increases with increasing x. Thus, the sample with the maximum ZT is TiNiSn_0.99Sb_0.01, with a value of ZT = 0.42 at 750 K. It can be said that Sb substitution for TiNiSn results in carrier doping and, at the optimum amount of substitution, improves the thermoelectric performance.

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