Influence of cation vacancy concentrations on ultra-low thermal conductivity in $(1-x)$BiVO$_4$-$x$Bi$_{2/3}$MoO$_4$ scheelite solid solutions

TL;DR

This study demonstrates that introducing a small amount of cation vacancies in BiVO$_4$-Bi$_2$MoO$_4$ solid solutions significantly reduces thermal conductivity, enhancing their potential for thermal barrier and thermoelectric applications.

Contribution

It provides new insights into how minimal cation vacancy concentrations can effectively lower thermal conductivity in scheelite solid solutions.

Findings

Thermal conductivity decreases from 1.74 to 1.12 W/mK with increasing vacancies.

A small vacancy concentration (1.7%) reduces thermal conductivity by over 15%.

Adding minimal vacancies improves thermoelectric and thermal barrier properties.

Abstract

Bismuth vanadate - bismuth molybdate solid-solution was prepared to elaborate ceramics with different amounts of cation vacancies. Dense ceramics with similar microstructures were obtained and the evolution of their melting point, specific heat, thermal diffusivity, and conductivity as a function of the amount of vacancy was evaluated. At room temperature, the thermal conductivity decreases from 1.74 W m$^{-1}$ K$^{-1}$ for BiVO$_{4}$ (x=0) to 1.12 W m$^{-1}$ K$^{-1}$ for Bi$_{0.867}$$\square$$_{0.133}$Mo$_{0.4}$V$_{0.6}$O$_{4}$ (x=0.4). Moreover, we show that a very small amount of vacancy (1.7%, x=0.05) is enough to provide a large decrease in thermal conductivity by more than 15%, in agreement with a mass fluctuation scattering model. However, the temperature of the melting point also decreases with increasing amount of vacancy. Our results suggest adding only a very small amount of vacancy as the best strategy to obtain superior materials for thermal barriers and thermoelectric devices, with ultra-low thermal conductivity and high-temperature stability.