Sodium diffusion in cryolite at elevated temperatures studied by quasielastic neutron scattering

Abstract

Quasielastic neutron scattering (QENS) has been applied to study the sodium mobility on nanosecond time scales in the perovskite fluoride cryolite, Na 3 AlF 6 , at high temperatures. Up to T = 1153 K the diffusion of Na ions is well described by a diffusion process of jumps between six and eight fold coordinated sites. Above this temperature, where a step-like increase in the electrical conductivity occurs, the jump length increases, which indicates additional jumps over larger distances. The electrical conductivity derived from the self-diffusion coefficient via the NernstEinstein relation and the corresponding activation energy are in excellent agreement with the previous conductivity measurements. We conclude that the jump diffusion of sodium ions is the dominant mechanism for the electrical conductivity in cryolite at high temperatures up to T = 1153 K.

Evaluation of sample cell materials for aqueous solutions used in quasi-elastic neutron scattering measurements

“…The oxidative and corrosive impact of the aqueous sample on Al can easily produce H 2 , HCl or Cl 2 gas (Vargel, 2020;Ghali, 2011), which may cause cell breakage. According to the literature (Dianoux & Lander, 2003), Nb (Winkler et al, 1994) and Mo (Demmel et al, 2009) have a low incoherent scattering cross section; they are known anticorrosive agents and are, at times, utilized as bioinert materials (Sharkeev et al, 2018). We performed the same corrosion tests at room temperature using a CaCl 2 solution for Nb and Mo and found no visual change or gas production on the substrates.…”

Quartz Cell for a Backscattering Spectrometer

“…Other low incoherent metals such as molybdenum [5], niobium [6], and platinum [7] are potential candidates as they are anticorrosive materials. Nevertheless, these materials involve machinability and base material cost.…”

The structure and vibrational spectroscopy of cryolite, Na3AlF6

“…2 The liquid phase of cryolite has been extensively investigated by a variety of techniques including multinuclear ( 19 F, 23 Na, 27 Al) NMR, [3][4][5] Raman spectroscopy [6][7][8] and quasielastic neutron scattering. 9,10 There are also a large number of molecular dynamics studies e.g. [11][12][13][14][15] , some of which calculate the Raman spectra 13,14 in the melt.…”