We report a characterization of the high-pressure behavior of zinc iodate, $\mathrm{Zn}{\left(\mathrm{I}{\mathrm{O}}_3\right)}_2$. By the combination of x-ray diffraction, Raman spectroscopy, and first-principles calculations we have found evidence of two subtle isosymmetric structural phase transitions. We present arguments relating these transitions to a nonlinear behavior of phonons and changes induced by pressure on the coordination sphere of the iodine atoms. This fact is explained as a consequence of the formation of metavalent bonding at high pressure which is favored by the lone-electron pairs of iodine. In addition, the pressure dependence of unit-cell parameters, volume, and bond distances is reported. An equation of state to describe the pressure dependence of the volume is presented, indicating that $\mathrm{Zn}{\left(\mathrm{I}{\mathrm{O}}_3\right)}_2$ is the most compressible iodate among those studied up to now. Finally, phonon frequencies are reported together with their symmetry assignment and pressure dependence.

• Received 16 November 2020
• Revised 24 January 2021
• Accepted 26 January 2021
• Corrected 19 March 2021

DOI:https://doi.org/10.1103/PhysRevB.103.054102