  We report the results of Raman spectroscopy high-pressure studies of alkali
metal fluoroargentates (M2AgF4, where M=Na, K, Rb) associated with theoretical
and x-ray diffraction studies for the K member of the series. Theoretical
density functional calculations predict two structural phase transitions for
K2AgF4: one from low pressure monoclinic P21/c (beta) phase to
intermediate-pressure tetragonal I4!2d structure at 6 GPa, and another to
high-pressure triclinic P1! phase at 58 GPa. However, Raman spectroscopy and
X-ray diffraction data indicate that both polymorphic forms of K2AgF4 as well
as two other fluoroargentate phases studied undergo amorphization at pressure
as low as several GPa.
