Identifying key descriptors in ZrSe2/HfSe2-based heterostructures and superlattices for enhancing thermoelectric performance

Abstract

Engineering a bilayer heterostructure (HS) and a superlattice monolayer (SLM) with trigonal symmetry not only provides versatile platforms for exploring material chemistry, but also opens avenues for thoroughly examining carrier transport mechanisms towards achieving high-performance thermoelectric materials. In this context, our study offers a comprehensive understanding of structural stability, particularly the role of interface coupling in influencing thermal transport and thermoelectric properties of ZrSe₂/HfSe₂ in bilayer HS and SLM forms. In this study, we employed various approaches, such as Debye–Callaway, Slack model, relaxation time approximation (RTA), and iterative methodology to obtain phonon transport coefficients and critically analyse the suitability of these approaches in computing lattice thermal conductivity for bilayer HS and SLM. The thermal properties study revealed the appearance of a soft optical mode at the zone-centre in bilayer HS, which plays a significant role in controlling phonon transport by enhancing three phonon scattering rates, particularly the prominent AAO and AOO scattering processes, while the scattering mechanism is completely non-identical in SLM. Conversely, the SLM structure also exhibits a staircase-like two-dimensional (2D) density of states, which is particularly beneficial for enhancing electronic transport and achieving competitive thermoelectric performance. We also identify useful descriptors, such as phonon group velocity, scattering rates, Grüneisen parameters, and phase-space volume, those characterize bilayer HS and SLM forms. Overall, our study provides new insights into materials chemistry governing phonon and electronic transport phenomena in bilayer HS and SLM and offers a broader perspective on interface coupling in assessing carrier transport properties in the field of thermoelectricity.