Room-temperature vibrational properties of potassium gadolinium double tungstate under compression up to 32 GPa

• Two phase transitions are pressure-induced in KGd(WO4)2 at 7.2, and 14.2 GPa.
• Raman-active modes and their pressure dependences are reported and discussed.
• Several modes showing a weak softening are found and related with structural changes.

KGd(WO4)2 has been studied by high-pressure Raman spectroscopy at room temperature up to 32.2 GPa. Evidences of two pressure-driven phase transitions have been detected. The low-pressure monoclinic phase undergoes a phase transition at 7.2(±0.9) GPa. The second transition is found at 14.2(±1.6) GPa. Both transitions are reversible. No evidence of pressure-induced amorphization is found up to 32 GPa. The pressure dependence of the Raman active modes of the low- and high-pressure phases is reported. A Raman mode is detected to exhibit a weak softening in the low-pressure phase. Three Raman modes are also observed to have a similar behavior in the second high-pressure phase. The reported results are discussed comparing with the studies available in related tungstates. Emphasis is placed on the physical implications of the results.

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