A high throughput search for efficient thermoelectric half-Heusler compounds

Half-Heusler compounds have emerged as promising thermoelectric materials that offer huge compositional space to tune their thermoelectric performance. A class of stable half Heusler compounds formed from elements of three specific groups in the periodic table viz. XpX ' 1-pYqY '(1-q)Z(r)Z '(1-r) (with X, X ' = Ti, Zr, Hf; Y, Y ' = Ni, Pd, Pt and Z, Z ' = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and 1) via various stoichiometric isoelectronic elemental substitutions at the X, Y and Z sites respectively, is investigated. Intelligent filters are employed at each step of our high throughput density functional theory calculations to filter compounds with improved figures of merit. While confirming several known results, the calculations also reveal unknown pathways to improve the thermoelectric performance of the compound class. The 50% X and Z site substitutions of the parent Heusler have been individually found to marginally enhance the power factor for both p- and n-type doping, while leading to considerable enhancement in the figure of merit (by similar to 24%) specifically. This is due to lowering of the lattice thermal conductivity stemming from the increase in lattice disorder in approximately the same cell volume. Furthermore, the present study confirms the experimental scenario that Y site substitution does not lead to enhancement of the power factor because of the breaking of band degeneracies at the high symmetry points. This work will serve as a consolidated cost effective guideline for experimentalists working with this compound class on enhancing the power factor and figure of merit of the compositions.