  We report a characterization of the high-pressure behavior of zinc-iodate,
Zn(IO3)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 non-linear 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 is reported. An equation
of state to describe the pressure dependence of the volume is presented,
indicating that Zn(IO3)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.
