Investigation of the phase transitions in the alkali metal nitrites using Raman spectroscopy

Walters, Robin V. (1989) Investigation of the phase transitions in the alkali metal nitrites using Raman spectroscopy. Masters thesis, Memorial University of Newfoundland.

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Abstract

The alkali metal nitrites have been studied from 77 K through the phase transitions and in the molten state by Raman spectroscopy. With the exception of LiNO₂, all the alkali metal nitrites go through at least one solid-solid phase transition. The presence of NO₂ groups disordered over non-equivalent crystallographic sites is a common feature of at least one phase for each salt. -- The results for LiNO₂ are not consistent with the suggested D⁵₃d crystal structure. Spectroscopic evidence and ab initio calculations indicated that the NaNO₂ order-disorder transition occurs via a nitrite rotation about the crystallographic a axis. No evidence was obtained for the reported phase transitions at 343 or 380 K in KNO₂ or for the high temperature phase transition in CsNO₂. For RbNO₂, the effect of nitrate impurity was considered. The spectroscopic observables are discussed in relation to available thermodynamic quantities.

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