Abstract:We report first principles calculations of the structural, electronic, elastic and vibrational properties of the semiconducting orthorhombic ZnSb compound. We study also the intrinsic point defects in order to eventually improve the thermoelectric properties of this already very promising thermoelectric material.Concerning the electronic properties, in addition to the band structure, we show that the Zn (Sb) crystallographically equivalent atoms are not exactly equivalent from the electronic point of view. Lattice dynamics, elastic and thermodynamic properties are found to be in good agreement with the experiments and they confirm the non equivalency of the zinc and antimony atoms from the vibrational point of view. The calculated elastic properties show a relatively weak anisotropy and the hardest direction is the y direction. We observe the presence of low energy modes involving both Zn and Sb atoms at about 5-6 meV, similarly to what has been found in Zn 4 Sb 3 and we suggest that the interactions of these modes with acoustic phonons could explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the most stable defects and this explains the intrinsic p-type conductivity of ZnSb.

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We report a combined theoretical and experimental search for thermoelectric materials based on semiconducting zinc antimony. Influence of three new doping elements (sodium, potassium and boron) on the electronic properties was investigated as well as the carrier concentration and temperature dependence of the thermoelectric coefficients obtained through density-functional calculations and Boltzmann transport theory. Distortion of the electron arrangement caused by the doping elements is displayed as a deformation charge density around the atoms. Based on the band structures, the density of states, and the transport properties, we found that the presence of Na and K in the ZnSb matrix leads to a slightly improved p-type conductivity, whereas the B substitution leads to a n-type doping. Because of the stronger need for obtaining n-type ZnSb-based material, the B(0.01)Zn(0.99)Sb structure has been transferred to the laboratory to be synthesized by direct melting. The sample was investigated using x-ray diffraction and scanning electron microscopy.

First principles calculations of the vibrational, thermodynamic and mechanical properties of the Ni-Ti-Sn Heusler and half-Heusler compounds have been performed. First, we have calculated the Raman and infrared spectra of NiTiSn, providing benchmark theoretical data directly useful for the assignments of its experimental spectra and clarifying the debate reported in the literature on the assignment of its modes. Then, we have discussed the significant vibrational density-of-states of Ni 2 TiSn at low-frequencies. These states are at the origin of (i) its smaller free energy, (ii) its higher entropy, and (iii) its lower Debye temperature, with respect to NiTiSn. Finally, we have reported the mechanical properties of the two compounds. In particular, we have found that the half-Heusler compound has the largest stiffness. Paradoxically, its bulk modulus is also the smallest. This unusual behavior has been related to the Ni-vacancies that weaken the structure under isostatic compression.Both compounds show a ductile behavior. I. INTRODUCTIONThe so-called Heusler and half-Heusler compounds have attracted intensive work during the last years. These compounds are a class of ternary intermetallics associating three elements in the following stoichiometric proportions 1:1:1 (Half-Heusler) or 2:1:1 (full-Heusler). They are represented by the general formula: XYZ and X 2 YZ, where X and Y are transition elements, and Z is a s or p-element. From the structural point of view, Heusler (resp. half-Heusler) compounds generally crystallise in the Fm3m (resp. F43m) space group with Cu 2 MnAl (resp. MgAgAs) as prototype 1 (see Fig. 1).New properties and potential fields of application constantly emerge 2 in these materials: topological insulators and spintronics are recent examples. Their properties can be easily predicted by the valence electron concentration (VEC) 3 and their extremely flexible electronic structure offers a lot of possibilities for tailoring these materials for interesting physical applications 2 (a detailed analysis of the density of states has been done in a separate study 4 ). Concerning more specifically the thermoelectric properties which we are interested in, it has been demonstrated that a arXiv:1309.7195v1 [cond-mat.mtrl-sci]