Enhanced thermopower in a magnetic semiconductor EuTe4 with multiple charge-density-wave instabilities/

TL;DR

This study reveals that EuTe4 exhibits highly stable charge-density wave states and exceptional thermoelectric properties near room temperature, driven by electron correlations and lattice instabilities, making it promising for thermoelectric applications.

Contribution

The paper demonstrates the coexistence of multiple charge-density wave states in EuTe4 and their impact on its thermoelectric performance, highlighting its potential as a novel thermoelectric material.

Findings

Charge-density wave state persists up to 650 K.

Seebeck coefficient exceeds 500 μV/K near room temperature.

Thermoelectric figure of merit zT reaches 0.22 at 460 K.

Abstract

We investigate the layered magnetic semiconductor EuTe4, focusing on its intricate charge-density wave (CDW) states near and above room temperature through single-crystal X-ray diffraction (XRD), magnetic, and thermoelectric measurements.The XRD measurement revealed that the CDW state inducing the polar lattice distortion persists even at 650 K, demonstrating its remarkable thermal stability. Notably, the Seebeck coefficient near room temperature reaches values exceeding 500 uVK-1. This large Seebeck coefficient, not fully captured by a simple band calculation, is comparable to those observed in heavy-electron semiconducting oxides, suggesting the importance of electron correlation and spin/lattice instabilities. Furthermore, potentially reflecting the competition of two types of CDW states, the thermal conductivity near room temperature is as low as 0.02 Wcm-1K-1. As a result, the thermoelectric figure of merit zT reaches 0.22 at 460 K. These findings establish EuTe4 as a compelling platform to explore novel types of thermoelectric materials with multiple electronic instability.