Pressure-induced phase changes in natural fluorapophyllite-(K) studied by Raman spectroscopy

Baoyun Wang; Meisu Xiang; Wansheng Xiao

doi:10.1016/j.saa.2024.125125

Pressure-induced phase changes in natural fluorapophyllite-(K) studied by Raman spectroscopy

Spectrochim Acta A Mol Biomol Spectrosc. 2024 Sep 14:325:125125. doi: 10.1016/j.saa.2024.125125. Online ahead of print.

Authors

Baoyun Wang¹, Meisu Xiang², Wansheng Xiao³

Affiliations

¹ College of Material and Chemical Engineering, Tongren University, Tongren 554300, China. Electronic address: wangbaoyun1992@163.com.
² College of Material and Chemical Engineering, Tongren University, Tongren 554300, China.
³ Guangdong Provincial Key Laboratory of Mineral Physics and Materials, 510640, China.

PMID: 39299074
DOI: 10.1016/j.saa.2024.125125

Abstract

The high-pressure Raman spectra in the low-wavenumber region (50-1200 cm^-1) and the hydroxyl stretching vibration region (2600-3800 cm^-1) of fluorapophyllite-(K) were collected in the interval of 0.0-50.7 GPa. Experimental results show that fluorapophyllite-(K) undergoes a crystalline-crystalline phase transition from a tetragonal structure (P4/mnc) to an orthorhombic structure (Pnnm) and then amorphization under high pressure conditions. Discontinuous changes in Raman peaks in the hydroxyl vibration region (2600-3800 cm^-1) and the low-wavenumber region (50-1200 cm^-1) occur at different onset pressures, suggesting that the destabilization of sub-lattices in fluorapophyllite-(K) under high pressure is not synchronous; the weak interlayer H₂O structural units are more prone to destabilization at lower pressures than the rigid SiO₄ tetrahedral layer units. Therefore, H₂O groups in fluorapophyllite-(K) serve as sensitive local probes during the pressure-induced phase transition and amorphization.

Keywords: Amorphization; Fluorapophyllite-(K); High pressure; Phase transition; Raman spectroscopy.