Bonding Hierarchy and Coordination Interaction Leading to High Thermoelectricity in Wide Bandgap TlAgI2

TL;DR

This paper reports on TlAgI2, a wide bandgap material with exceptionally low thermal conductivity and high thermoelectric efficiency, achieved through unique bonding and electronic interactions.

Contribution

It introduces a novel wide bandgap thermoelectric material, TlAgI2, with high ZT driven by bonding hierarchy and coordination interactions, surpassing conventional limits.

Findings

ZT of 2.20 at 300 K for p-type TlAgI2

Lattice thermal conductivity of 0.3 W/m·K at 300 K

Wide bandgap of 1.55 eV enhances thermoelectric performance

Abstract

High thermoelectric properties are associated with the phonon-glass electron-crystal paradigm. Conventional wisdom suggests that the optimal bandgap of semiconductor to achieve the largest power factor should be between 6 and 10 kbT. To address challenges related to the bipolar effect and temperature limitations, we present findings on Zintl-type TlAgI2, which demonstrates an exceptionally low lattice thermal conductivity of 0.3 W m-1 K-1 at 300 K. The achieved figure of merit (ZT) for TlAgI2, featuring a 1.55 eV bandgap, reaches a value of 2.20 for p-type semiconductor. This remarkable ZT is attributed to the existence of extended antibonding states Ag-I in the valence band. Furthermore, the bonding hierarchy, influencing phonon anharmonicity, and coordination bonds, facilitating electron transfer between the ligand and the central metal ion, significantly contribute to electronic transport. This finding serves as a promising avenue for the development of high ZT materials with wide bandgaps at elevated temperatures.