  X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and
CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil
cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I-42m) up
to 15.5 GPa and in the range from 15.5 GPa to 18.5 GPa the low-pressure phase
coexists with a high-pressure phase, which remains stable up to 23 GPa. In
CdGa2S4, we find the defect tetragonal chalcopyrite-type structure (I-4) is
stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition
takes place. In both materials, the high-pressure phase has been characterized
as a defect-cubic NaCl-type structure (Fm-3m). The occurrence of the pressure
induced phase transitions is apparently related with an increase of the cation
disorder on the semiconductors investigated. In addition, the results allow the
evaluation of the axial compressibility and the determination of the equation
of state for each compound. The obtained results are compared with those
previously reported for isomorphic digallium sellenides. Finally, a systematic
study of the pressure-induced phase transition in twenty-three different
sphalerite-related ABX2 and AB2X4 compounds indicates that the transition
pressure increases as the ratio of the cationic radii and anionic radii of the
compounds increases.
