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The effective carrier masses are often calculated by a fitting of energy bands along the high symmetry lines, which is not accurate. In this method, the effective mass is very important to the calculation of relaxation time (τ). In our study, we use the deformation potential (DP) theory combined with the effective mass approximation to calculate the relaxation time (τ) which is no longer treated as a constant. This drawback damages the reliability of the predicted properties. Even though, earlier calculations on these parameters (σ, S, κ e) utilizing this semi-classic theory relies on a constant relaxation time (τ) or non-constant relaxation time obtained from the experimental data 12, 17, 18 which are certainly questionable for many cases. First of all, given reliable knowledge on electronic structure as produced by the ab-initio calculations and/or experimental probing using techniques like angle-resolved photoelectron spectroscopy for a TE compound, indeed the semi-classic Boltzmann transport theory can be employed to predict the σ, S and κ e. There exist two major challenges for an accurate calculation of these TE properties. However, such a scheme remains yet to be found, in particular for carrier-doped TE materials. Nevertheless, developing a full-scale computation scheme for the TE properties of a material to guide the experimental search is still appealed. 16 proposed an approach of data mining to search for novel TE materials, both of which are of significance. 15 developed a scheme to calculate the carrier mobility, effective mass and lattice thermal conductivity related to TE performances and Sparks et al. As a result, a theoretical prediction from first-principles calculations and other methods has been of interest for a long time 13, 14, 15, 16. These issues are thus appealing materials computation and property design as a pre-requisite for exploring TE materials for favorable applications. By the way, technically, a reliable measurement of the κ tot and evaluation of its two components (κ l, κ e) seem to be tricky and thus the reported data are sometimes authors-dependent. Given this dilemma, an optimization of all these properties so that the largest PF and ZT can be obtained simultaneously is far beyond fast-track experimental explorations. Good electrical conduction usually corresponds to high thermal conductivity and a counteracted relationship between the S and σ is often observed, resulting in the complex relationships between these physical parameters ( S, T, σ, κ l and κ e). Conceptually, in order to possess a large ZT, the PF must be large and the total thermal conductivity κ tot should be minimized. The thermally-driven electrical performance of a TE material is measured by the power factor ( PF = S 2σ), while a high heat-to-electricity conversion efficiency is scaled by ZT.
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A good TE material should have high figure of merit ZT = ( S 2σ/κ tot) T, where S, σ, κ tot (=κ l + κ e), T, represent the Seebeck coefficient, electrical conductivity, total thermal conductivity and absolute temperature and κ l and κ e are the lattice and electronic components, respectively.
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Thermoelectric (TE) power generators that enable the direct conversion from heat to electricity have been studied for a long time, much earlier than the claimed energy crisis 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.Īt least as much as the energy we used on earth is lost in the form of waste heat 1. The calculated results show good agreement with experimental data. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory.
#Half heusler phono dispersio code#
The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT.
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