Thermoelectric transport in Ru$_2$TiSi full-Heusler compounds

TL;DR

This study combines theoretical and experimental approaches to show that p-type Ru$_2$TiSi full-Heusler compounds have high thermoelectric efficiency, with potential for practical applications due to their high figure of merit at elevated temperatures.

Contribution

It introduces Ru$_2$TiSi as a promising thermoelectric material with superior performance compared to similar compounds, highlighting the importance of p-type doping and thermal conductivity reduction.

Findings

High thermoelectric figure of merit ($zT > 1$) at 700 K in p-type Ru$_2$TiSi.

Lighter, more mobile holes from dispersive valence bands enhance thermoelectric performance.

Larger band gap of Ru$_2$TiSi suggests better thermoelectric efficiency than Fe$_2$VAl.

Abstract

Heusler compounds with six valence electrons per atom have attracted interest as thermoelectric materials owing to their semimetallic and semiconducting properties. Here, we theoretically and experimentally investigate electronic transport in Ru$_2$TiSi-based full-Heuslers. We show that electronic transport in this system can be well captured by a two-parabolic band model. The larger band gap of Ru$_2$TiSi promises a higher thermoelectric performance, compared to its isovalent family member Fe$_2$VAl, which has been studied as a thermoelectric material for over two decades. Additionally, we identify $p$-type Ru$_2$TiSi as far more efficient than previously studied $n$-type compounds and demonstrate that this can be traced back to much lighter and more mobile holes originating from dispersive valence bands. Our findings demonstrate that an exceptionally high dimensionless figure of merit $zT > 1$ can be realized in these $p$-type compounds around 700 K upon proper reduction of the lattice thermal conductivity, e.g., by substituting Zr or Hf for Ti.