# Thermoelectric Properties of Zn-Doped YbMg1.85−xZnxBi1.98

## TL;DR

This study explores how Zn doping affects the thermoelectric properties of YbMg1.85−xZnxBi1.98, finding that moderate Zn levels improve performance but excessive doping reduces efficiency.

## Contribution

The paper provides new insights into the optimal Zn doping level for enhancing thermoelectric performance in YbMg2Bi1.98 compounds.

## Key findings

- Electrical conductivity increases with Zn doping, while lattice thermal conductivity decreases.
- Zn doping reduces the band gap, causing bipolar conduction and higher thermal conductivity at elevated temperatures.
- Maximum Zn doping is recommended to be less than x = 0.1 to maintain optimal thermoelectric performance.

## Abstract

Bi-based YbMg2Bi1.98 Zintl compounds represent promising thermoelectric materials. Precise composition and appropriate doping are of great importance for this complex semiconductor. Here, the influence of Zn substitution for Mg on the microstructure and thermoelectric properties of p-type YbMg1.85−xZnxBi1.98 (x = 0, 0.05, 0.08, 0.13, 0.23) was investigated. Polycrystalline samples were prepared using induction melting and densified with spark plasma sintering. X-ray diffraction confirmed that the major phase of the samples possesses the trigonal CaAl2Si2-type crystal structure, and SEM/EDS indicated the presence of minor secondary phases. The electrical conductivity increases and the lattice thermal conductivity decreases with more Zn doping in YbMg1.85−xZnxBi1.98, whereas the Seebeck coefficient has a large reduction. The band gap decreases with increasing Zn concentration and leads to bipolar conduction, resulting in an increase in the thermal conductivity at higher temperatures. Figure of merit ZT values of 0.51 and 0.49 were found for the samples with x = 0 and 0.05 at 773 K, respectively. The maximum amount of Zn doping is suggested to be less than x = 0.1.