Abstract
Since the last decade, the half-Heusler (HH) compounds have taken an important place in the field of the condensed matter physics research. The multiplicity of substitutions of transition elements at the crystallographic sites X, Y and (III-V) elements at the Z sites, gives to the HH alloys a multitudes of remarkable properties. In the present study, we examined the structural, electronic and thermoelectric properties of ZrCoBi0.75Z0.25 (Z = P, As, Sb) using density functional theory (DFT). The computations have been done parallel to the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2k code. The thermoelectrically properties were predicted via the semi-classical Boltzmann transport theory, as performed in Boltztrap code. The obtained results for the band structure and densities of states confirm the semiconductor (SC) nature of the three compounds with an indirect band gap, which is around 1eV. The main thermoelectric parameters such as Seebeck coefficient, thermal conductivity, electrical conductivity and figure of merit were estimated for temperatures ranging from zero to 1200K. The positive values of Seebeck coefficient (S) confirm that the ZrCoBi0.75Z0.25 (x = 0 and 0.25) are a p-type SC. At the ambient temperature, ZrCoBi0.75P0.25 exhibit the large S value of 289 µV/K, which constitutes an improvement of 22% than the undoped ZrCoBi, and show also a reduction of 54% in thermal conductivity (κ/τ). The undoped ZrCoBi has the lowest ZT value at all temperatures and by substituting bismuth atom by one of the sp elements (P, As, Sb), a simultaneous improvement in κ/τ and S have led to maximum figure of merit (ZT) values of about 0.84 obtained at 1200 K for the three-doped compounds.
Highlights
Since the last decade, the half-Heusler (HH) compounds have taken an important place in the field of the condensed matter physics research
The crystal structures of ZrCoBi0.75Z0.25 (Z = P, As, Sb) are cubic with the space group of P-43m; the structure can be regarded as four interpenetrating fcc sublattices (Fig. 1b)
By using the first-principle density-functional theory within the supercell approach, we have studied the ZrCoBi0.75Z0.25 (Z = P, As, Sb) half-Heusler, a particular emphasis was placed on the thermoelectric properties
Summary
The half-Heusler (HH) compounds have taken an important place in the field of the condensed matter physics research. We examined the structural, electronic and thermoelectric properties of ZrCoBi0.75Z0.25 (Z = P, As, Sb) using density functional theory (DFT). The undoped ZrCoBi has the lowest ZT value at all temperatures and by substituting bismuth atom by one of the sp elements (P, As, Sb), a simultaneous improvement in κ/τ and S have led to maximum figure of merit (ZT) values of about 0.84 obtained at 1200 K for the three-doped compounds. Y.Lei et al [14] have explored the impact of Sb doping on thermoelectric properties of TiNiSn HH, they noted that the ZT value is moderately improved from 0.30 for undoped alloy to 0.44 for a dopant concentration of 3%. We studied the electronic and thermoelectric properties of sp elements (P, As, Sb)-doped ZrCoBi half-Heusler alloy. A particular emphasis was placed on the thermoelectric properties investigated by the semi-classical Boltzmann theory
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