Thermoelectric properties, efficiency and thermal expansion of ZrNiSn half-Heusler by first-principles calculations

Abstract

In this work, we try to understand the experimental thermoelectric (TE) properties of a ZrNiSn sample with DFT and semiclassical transport calculations using SCAN functional. SCAN and mBJ provide the same band gap Eg of ∼0.54 eV. This Eg is found to be inadequate to explain the experimental data. The better explanation of experimental Seebeck coefficient S is done by considering Eg of 0.18 eV which suggests the non-stoichiometry and/or disorder in the sample. Further improvement in the S is done by the inclusion of temperature dependence on chemical potential. In order to look for the possible enhanced TE properties obtainable in ZrNiSn with Eg of ∼0.54 eV, power factor and optimal carrier concentrations are calculated. The optimal electron and hole concentrations required to attain highest power factors are ∼7.6x10 19 cm −3 and ∼1.5x10 21 cm −3 , respectively. The maximum figure of merit ZT calculated at 1200 K for n-type and p-type ZrNiSn are ∼0.6 and ∼0.7, respectively. The % efficiency obtained for n-type ZrNiSn is ∼5.1 % while for p-type ZrNiSn is ∼6.1 %. The ZT are expected to be further enhanced to ∼1.2 (n-type) and ∼1.4 (p-type) at 1200 K by doping with heavy elements for thermal conductivity reduction. The phonon properties are also studied by calculating dispersion, total and partial density of states. The calculated Debye temperature of 382 K is in good agreement with experimental value of 398 K. The thermal expansion behaviour in ZrNiSn is studied under quasi-harmonic approximation. The average linear thermal expansion coefficient αave(T ) of ∼7.8x10 −6 K −1 calculated in our work is quite close to the experimental values. The calculated linear thermal expansion coefficient will be useful in designing the thermoelectric generators for high temperature applications.

Density functional study of thermodynamic properties, thermal expansion and lattice thermal conductivity of Fe2VAl in the high-temperature region

“…Introduction. -Phonons play an important role in understanding many properties of the materials, such as thermal conductivity [1][2][3], thermal expansion [4][5][6], thermoelectricity [7,8], superconductivity [9,10], mechanical properties [11,12], etc. Understanding the phononic transport properties has always been a challenging task at the level of theory as well as computation.…”

First-principles electronic structure, phonon properties, lattice thermal conductivity and prediction of figure of merit of FeVSb half-Heusler

“…The value of maximum PF at 1200 K are ∼98 and ∼200 PFU for n-type and p-type doping, respectively. This value of maximum PF due to hole doping obtainable in FeVSb is higher compared to that in ZrNiSn studied in our previous work [17]. Suggesting the value of optimal carrier concentrations for doping is useful rather than the µ values to realize the reported thermoelectric properties.…”

“…Therefore, question arises what may be the right band gap of FeVSb which can better explain the experimental S. Therefore, under rigid band approximation, the band gap values are varied in the range 0.2 eV to 0.7 eV and S values are calculated. In calculating the S, the temperature dependence on the chemical potential was included using the below relation [17,36],…”

Thermoelectric properties of Fe$_{2}$VAl at high temperature region: A combined experimental and theoretical study

“…These compounds are desirable for thermoelectric applications due to possessing large S, moderate σ, high temperature stability, non-toxic, mechanical strength etc 14,15 . Number of experimental and theoretical TE studies on Heusler compounds have been carried out in last few decades [16][17][18][19][20][21][22][23][24][25] . Among the existing Heusler compounds, the Fe 2 VAl-based compounds have attracted considerable attention in the TE community 26,27 .…”