We use powder x-ray diffraction to study the effect of pressure on the crystal structure of the honeycomb rhodate ${\mathrm{Li}}_2{\mathrm{RhO}}_3$. We observe low-pressure ($P<P_{c1}=6.5\mathrm{GPa}$) and high-pressure ($P>P_{c2}=14\mathrm{GPa}$) regions corresponding to the monoclinic $C2/m$ symmetry, while a phase mixture is observed at intermediate pressures. At $P>P_{c2}$, the honeycomb structure becomes distorted and features short Rh-Rh bonds forming zigzag chains stretched along the crystallographic $a$ direction. This is in contrast to dimerized patterns observed in triclinic high-pressure polymorphs of $\alpha \text{−}{\mathrm{Li}}_2{\mathrm{IrO}}_3$ and $\alpha \text{−}{\mathrm{RuCl}}_3$. Density-functional theory calculations at various pressure conditions reveal that the observed rhodium zigzag-chain pattern is not expected under hydrostatic pressure but can be reproduced by assuming anisotropic pressure conditions.

• Received 7 May 2019

DOI:https://doi.org/10.1103/PhysRevB.100.064105