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Abstract Bi₂SeO₂is a promisingn‐type semiconductor to pair withp‐type BiCuSeO in a thermoelectric (TE) device. The TE figure of meritzTand, therefore, the device efficiency must be optimized by tuning the carrier concentration. However, electron concentrations in self‐dopedn‐type Bi₂SeO₂span several orders of magnitude, even in samples with the same nominal compositions. Such unsystematic variations in the electron concentration have a thermodynamic origin related to the variations in native defect concentrations. In this study, first‐principles calculations are used to show that the selenium vacancy, which is the source ofn‐type conductivity in Bi₂SeO₂, varies by 1–2 orders of magnitude depending on the thermodynamic conditions. It is predicted that the electron concentration can be enhanced by synthesizing under more Se‐poor conditions and/or at higher solid‐state reaction temperatures (T_SSR), which promote the formation of selenium vacancies without introducing extrinsic dopants. The computational predictions are validated through solid‐state synthesis of Bi₂SeO₂. More than two orders of magnitude increase are observed in the electron concentration simply by adjusting the synthesis conditions. Additionally, a significant effect of grain boundary scattering on the electron mobility in Bi₂SeO₂is revealed, which can also be controlled by adjusting T_SSR. By simultaneously optimizing the electron concentration and mobility, azTof ≈0.2 is achieved at 773 K for self‐dopedn‐type Bi₂SeO₂. The study highlights the need for careful control of thermodynamic growth conditions and demonstrates TE performance improvement by varying synthesis parameters according to thermodynamic guidelines. 

Abstract Engineering semiconductor devices requires an understanding of charge carrier mobility. Typically, mobilities are estimated using Hall effect and electrical resistivity meausrements, which are are routinely performed at room temperature and below, in materials with mobilities greater than 1 cm²V^‐1s^‐1. With the availability of combined Seebeck coefficient and electrical resistivity measurement systems, it is now easy to measure the weighted mobility (electron mobility weighted by the density of electronic states). A simple method to calculate the weighted mobility from Seebeck coefficient and electrical resistivity measurements is introduced, which gives good results at room temperature and above, and for mobilities as low as 10⁻³cm²V^‐1s^‐1,Here, μ_wis the weighted mobility, ρ is the electrical resistivity measured in mΩ cm,Tis the absolute temperature in K,Sis the Seebeck coefficient, andk_B/e = 86.3 µV K^–1. Weighted mobility analysis can elucidate the electronic structure and scattering mechanisms in materials and is particularly helpful in understanding and optimizing thermoelectric systems. 

Abstract Highly resistive grain boundaries significantly reduce the electrical conductivity that compromises the thermoelectric figure‐of‐meritzTin n‐type polycrystalline Mg₃Sb₂. In this work, discovered is a Mg deficiency near grain boundaries using atom‐probe tomography. Approximately 5 at% of Mg deficiency is observed uniformly in a 10 nm region along the grain boundary without any evidence of a stable secondary or impurity phase. The off‐stoichiometry can prevent n‐type dopants from providing electrons, lowering the local carrier concentration near the grain boundary and thus the local conductivity. This observation explains how nanometer scale compositional variations can dramatically determine thermoelectriczT, and provides concrete strategies to reduce grain‐boundary resistance and increasezTin Mg₃Sb₂‐based materials.