Raman and theoretical studies on structural evolution of Li2BeF4 and binary LiF-BeF2 melts

• Published in: Journal of molecular liquids 2021-03, Vol.325, p.115208, Article 115208
• Main Authors: Li, Yangjuan, Liu, Xiyan, Wang, Baozhu, Wang, Chenyang
• Format: Article
• Language: English
• Subjects: Density functional theory; Li2BeF4; LiF-BeF2 melts; Raman spectroscopy
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2020.115208

The structural evolution of Li2BeF4 from crystalline to molten states has been investigated by Raman spectroscopic technique with the assist of density functional theory (DFT). The experimental results of temperature-dependent Raman spectra of Li2BeF4 showed that no solid-state phase transformation was taken place during heating process from 298 to 723 K. In the molten state, the structure of BeF42− anion was affected by Li+ cation and environment. For the binary LiF-BeF2 melts with varying LiF/BeF2 ratio, the stretching bands of beryllium‑fluorine bonds in molten Raman spectra were deconvolved identified by Gaussian function. When the concentration of BeF2 exceeding 33 mol%, the dimer Be2F73− was formed and dominated the spectrum. It was characterized to have a linear Be–F–Be geometry with two BeF4 moieties bridged by a single fluorine atom. A second anion Be3F104− processing a triple chain structure formed when the content of BeF2 increasing to 50 mol%. When the concentration of BeF2 went beyond 60 mol%, the Raman intensity and band width gradually decreased. While the intensity and band width of Raman spectra gradually decreased with the concentration of BeF2 exceeding to 60 mol%, which suggests that the band should be assigned to a hexatomic Be6F186− ring which was similar to the situation in the pure BeF2 network structure. •The structure of beryllium fluorides was studied by Raman and DFT calculations.•Different models and methods were established to simulate crystal and melt.•Fluoroberyllate species BeF42−, Be2F73−, Be3F104−, and Be6F186− were observed.