Phase transitions and amorphization of M2AgF4 (M = Na, K, Rb) compounds at high pressure

TL;DR

This study investigates how alkali metal fluoroargentates, specifically K2AgF4, undergo phase transitions and amorphization under high pressure, combining experimental Raman spectroscopy with theoretical calculations.

Contribution

It reveals that despite predicted structural phase transitions, these compounds amorphize at relatively low pressures, challenging existing theoretical expectations.

Findings

K2AgF4 transitions from monoclinic to tetragonal at 6 GPa

Amorphization occurs at pressures as low as a few GPa

Both experimental and theoretical results show discrepancies in phase behavior

Abstract

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.