Atomistic study of an ideal metal/thermoelectric contact: The full-Heusler/half-Heusler interface

Abstract

Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are important thermoelectric materials for converting waste heat into electricity. Reduced electrical resistivity at the hot interface between the half-Heusler material and a metal contact is critical for device performance, however this has yet to be achieved in practice. Recent experimental work suggests that a coherent interface between half-Heusler and full-Heusler compounds can form due to diffusion of transition metal atoms into the vacant sublattice of the half-Heusler lattice. We study theoretically the structural and electronic properties of such an interface using a first-principles based approach that combines ab initio calculations with macroscopic modeling. We find that the prototypical interface HfNi2Sn/HfNiSn provides very low contact resistivity and almost ohmic behavior over a wide range of temperatures and doping levels. Given the potential of these interfaces to remain stable over a wide range of temperatures, our study suggests that full-Heuslers might provide nearly ideal electrical contacts to half-Heuslers that can be harnessed for efficient thermoelectric generator devices.

Energy Filtering of Charge Carriers: Current Trends, Challenges, and Prospects for Thermoelectric Materials

“…It was also noted that these parameters are strictly composition dependent, so that any slight variation in composition modifies the properties. Spataru et al theoretically studied the structural and electronic properties of FH/HH interfaces . Having good lattice matching between the crystal structures of FH and HH, these coherent interfaces are stable for a wide temperature range.…”

“…Having good lattice matching between the crystal structures of FH and HH, these coherent interfaces are stable for a wide temperature range. The contact resistivity near the coherent interface exhibits Ohmic behavior for the entire temperature range . For HH compounds, Makongo et al proposed an effect, namely, “atomic scale structural engineering of thermoelectrics,” which is a combined effect of EF and electron injection that is able to produce a large PF 8f.…”

Reliable metal alloy contact for Mg3+δBi1.5Sb0.5 thermoelectric devices

“…As the main components of the most common contact materials, transition metals, such as Nb, Fe, Mn, Ta, Co, etc., can effectively alter the charge-transport properties of the TE material [19] . This has recently been found for n-type Mg 3 Sb 2 [16,20] , but it must be emphasized that contacts for Bi-rich n-type Mg +δ Bi 2-x Sb x have not yet been extensively explored. The phase diagrams or the formation energy values for Sb-and Bi-rich compounds in this system could be completely different when forming contacts with transition metals.…”

“…Materials incorporating Ni, Fe, Co, Ag, Mo, etc. have been tested as contacts for TE materials such as Bi 2 Te 3 , Mg 3 Sb 2 , Mg 2 Si, PbTe, and half-Heusler compounds [10,[15][16][17][18] . However, the underlying mechanism remains obscure, and there is no general rule to follow in contact design.…”

Half-Heusler Structures with Full-Heusler Counterparts: Machine-Learning Predictions and Experimental Validation

“…For example, as vacancies are gradually introduced in MnNi 2– x Sb ( x = 0–1), the structure transforms from full- to half-Heusler, and the magnetocaloric response is modified. , This transformation could also be described in the reverse way as the occupation of interstitial sites on progressing from the half- to full-Heusler structure in MnNi 1+ x Sb ( x = 0–1). An exciting recent development is the application of this disorder phenomenon to improve the performance of thermoelectric devices by “nanostructuring,” in which interfaces are constructed between full- and half-Heusler structures. − …”