Phase transformations in LiH 2 PO 4 (LDP) revealed by Raman spectroscopy

Abstract

We investigate Raman scattering measurements on polycrystalline LiH 2 PO 4 (LDP) between 30 and 240°C, in order to detect phase transformations. The thermal behavior of main lines in different wavenumber ranges is discussed and analyzed. Raman spectra show two anomalies at 176°C and 210°C, reflecting changes in chemical bonds, and are attributed to progressive polymerization, in agreement with earlier electrical measurements.

Vapor pressure and specific electrical conductivity in the H2O–LiH2PO4–LiPO3 system—a novel electrolyte for water electrolysis at elevated temperature

“…These experiments were done using a 532 nm green laser, a LabRam Raman microscope with a 50X objective on crystals placed in a Linkam heating module at a distance of 1 cm. When recording spectra from 30 °C to 240 °C two sudden abnormal wavenumber shifts were detected at around 176 and 210 °C for all main Raman lines, reflecting occurrence of large changes in the chemical bonding properties [34]. Broad stretching bands between 2600 and 3600 cm -1 gradually change to a very intense and wide signal.…”

“…More recently, Dekhili et al [34] performed Raman measurements on polycrystalline LDP with special attention on detecting phase transformations at temperatures up to ∼220 °C. These experiments were done using a 532 nm green laser, a LabRam Raman microscope with a 50X objective on crystals placed in a Linkam heating module at a distance of 1 cm.…”

“…The conductivity mechanism of LiH2PO4 was previously studied by means of many techniques, e.g. Raman spectroscopy [33][34], nuclear magnetic resonance (NMR), and High Field magic angle spinning (MAS) NMR, and it was shown that the conductivity in LDP can be directly ascribed to protonic mobility [35][36][37][38][39]. By means of rotating-frame NMR the proton dynamics in LDP was found to be strictly coupled to the re-orientation motion of the PO4 3tetrahedra [36].The proton movement is thought to happen via hydrogen jumps helped by bond vibrations and reorientation oscillations of the phosphate anions, especially at higher temperatures.…”

Raman spectra in LiH2PO4 and KLi(H2PO4)2: Mode assignment

“…Measurements were performed from 30°C to 176°C on a polycrystalline LDP sample and from 30°C to 120°C on a KLDP single crystal. These temperature ranges have been chosen below the first structural transformations occurring at about 176°C in LDP and 125°C in KLDP. Thus, non‐monotonous changes in Raman lines caused by structural transitions were not considered here.…”

Three new acidM+arsenates and phosphates with multiply protonated As/PO4groups

“…M + phosphates and arsenates, and their crystal structures and physicochemical properties, have been extensively studied. Several compounds exhibit interesting properties, such as protonic conductivity (Chouchene et al, 2017a,b;Volkov et al, 1995Volkov et al, , 1997Voronov et al, 2013;Dekhili et al, 2018) or nonlinear optical properties (Dhouib et al, 2014a(Dhouib et al, , 2017Kumaresan et al, 2008).…”