Thermal decomposition of the Kitaev material $\alpha$-RuCl$_3$ and its influence on low-temperature behavior

TL;DR

This study investigates how heat treatment affects the composition and low-temperature properties of $ ext{α}$-RuCl$_3$, revealing significant oxidation and impurity effects that alter electrical and thermal behaviors.

Contribution

It provides detailed analysis of thermal decomposition and impurity formation in $ ext{α}$-RuCl$_3$, linking heat treatment to changes in physical properties.

Findings

Dechlorination and oxidation occur above 300°C.

RuO$_2$ impurities increase up to 20% after annealing.

Impurities significantly reduce electrical resistance.

Abstract

We explore the effect of heat treatment in argon atmosphere under various temperatures up to $500^\circ$C on single crystals of $\alpha$-RuCl$_3$ by study of the mass loss, microprobe energy dispersive x-ray spectroscopy, powder x-ray diffraction, electrical resistance as well as low-temperature magnetic susceptibility and specific heat. Clear signatures of dechlorination and oxidation of Ru appear for annealing temperatures beyond $300^\circ$C. Analysis of the specific heat below 2~K reveals a RuO$_2$ mass fraction of order $1\%$ for pristine $\alpha$-RuCl$_3$ which increases up to $20\%$ after thermal annealing, fully consistent with mass-loss analysis. The small RuO$_2$ inclusions drastically reduce the global electrical resistance and may thus significantly affect low-temperature thermal transport and Hall effect.