# Orbital-selective band engineering realizes high zT in p-type Ru2Ti1−xHfxSi full-Heusler thermoelectrics

## TL;DR

Scientists discovered a new class of thermoelectric materials with high efficiency, achieved through orbital-selective substitution in full-Heusler compounds.

## Contribution

The discovery of p-type Ru2Ti1−xHfxSi full-Heusler thermoelectrics with a high zT of 0.7, the highest reported for this material class.

## Key findings

- p-type Ru2Ti1−xHfxSi full-Heusler compounds achieve a zT of 0.7 between 700–1000 K.
- Orbital-selective substitution enhances thermoelectric performance by scattering lattice vibrations without affecting charge carriers.
- Strategies are proposed to further increase zT beyond 1 in these materials.

## Abstract

Heusler compounds have emerged as important thermoelectric materials due to their combination of promising electronic transport properties, mechanical robustness and chemical stability – key aspects for practical device integration. While a wide range of XYZ-type half-Heusler compounds have been studied for high-temperature applications, X2YZ-type full-Heuslers, often characterized by narrower band gaps, may offer potential advantages at different temperature regimes but remain less explored. In this work, the discovery of p-type Ru2Ti1−xHfxSi full-Heusler thermoelectrics, exhibiting a high figure of merit zT = 0.7 over a broad range of temperatures 700–1000 K, is reported. These results not only represent the largest values known to date among full-Heusler materials but confirm earlier theoretical predictions that p-type Ru2TiSi systems would be superior to their n-type counterparts. Moreover, using a two-band model, electronic structure changes induced by the Hf substitution at the Ti site are unveiled and strategies to further improve zT up to zT > 1 are outlined. These findings highlight the untapped potential of new semiconducting full-Heusler phases and the crucial need for continued exploration of this rich materials class for thermoelectric applications.

Authors discover a class of p-type thermoelectric full-Heusler compounds and show that by orbital-selective substitution, lattice vibrations can be scattered but charge carriers remain unscathed, yielding a high zT among full-Heusler materials.