The Seebeck coefficient is one of the key quantities of thermoelectric materials and routinely measured in various laboratories. There are, however, several ways to calculate the Seebeck coefficient from the raw measurement data. We compare these different ways to extract the Seebeck coefficient, evaluate the accuracy of the results, and show methods to increase this accuracy. We furthermore point out experimental and data analysis parameters that can be used to evaluate the trustworthiness of the obtained result. The shown analysis can be used to find and minimize errors in the Seebeck coefficient measurement and therefore increase the reliability of the measured material properties.

Figure of merit zT mapping of p-Mg₂Si_1−xSn_x with respect to carrier concentration.

The crystal structures of new layered manganese bismuth tellurides with the compositions Mn_0.85(3)Bi_4.10(2)Te₇ and Mn_0.73(4)Bi_6.18(2)Te₁₀ were determined by single-crystal X-ray diffraction, including the use of microfocused synchrotron radiation. These analyses reveal that the layered structures deviate from the idealized stoichiometry of the 12P-GeBi₄Te₇ (space group Pm1) and 51R-GeBi₆Te₁₀ (space group Rm) structure types they adopt. Modified compositions Mn_1−xBi_4+2x/3Te₇ (x = 0.15–0.2) and Mn_1−xBi_6+2x/3Te₁₀ (x = 0.19–0.26) assume cation vacancies and lead to homogenous bulk samples as confirmed by Rietveld refinements. Electron diffraction patterns exhibit no diffuse streaks that would indicate stacking disorder. The alternating quintuple-layer [M₂Te₃] and septuple-layer [M₃Te₄] slabs (M = mixed occupied by Bi and Mn) with 1 : 1 sequence (12P stacking) in Mn_0.85Bi_4.10Te₇ and 2 : 1 sequence (51R stacking) in Mn_0.81Bi_6.13Te₁₀ were also observed in HRTEM images. Temperature-dependent powder diffraction and differential scanning calorimetry show that the compounds are high-temperature phases, which are metastable at ambient temperature. Magnetization measurements are in accordance with a Mn^II oxidation state and point at predominantly ferromagnetic coupling in both compounds. The thermoelectric figures of merit of n-type conducting Mn_0.85Bi_4.10Te₇ and Mn_0.81Bi_6.13Te₁₀ reach zT = 0.25 at 375 °C and zT = 0.28 at 325 °C, respectively. Although the compounds are metastable, compact ingots exhibit still up to 80% of the main phases after thermoelectric measurements up to 400 °C.