Single crystal growth by self-flux method of the mixed valence gold halides Cs$_2$[Au$^{I}$X$_2$][Au$^{III}$X$_4$] (X=Br,I)

TL;DR

This study reports the growth and structural analysis of high-quality single crystals of mixed valence gold halides Cs$_2$Au$_2$X$_6$ (X=Br,I), revealing their distorted perovskite structure and large bandgaps, with initial substitution attempts explored.

Contribution

First successful growth of high-quality single crystals of Cs$_2$Au$_2$X$_6$ using a self-flux method and detailed structural and electronic characterization.

Findings

Crystals have a distorted perovskite structure in I4/mmm space group.

Cs$_2$Au$_2$I$_6$ has a bandgap of 550 ± 100 meV.

Cs$_2$Au$_2$Br$_6$ has a bandgap of 520 ± 80 meV.

Abstract

High quality single crystals of Cs$_2$Au$_2$X$_6$ (X=Br,I) were grown using a ternary self-flux method. Structural refinements based on single crystal X-ray diffraction measurements show that both materials have a distorted perovskite structure belonging to the I4/mmm space group with full site occupancy. Transport measurements reveal a large bandgap of 550 $\pm$ 100 meV for Cs$_2$Au$_2$I$_6$ and 520 $\pm$ 80 meV for Cs$_2$Au$_2$Br$_6$. Initial attempts at chemical substitution are described.