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Abstract

The nature of the disorder present in Na3ONO2 has been studied
using variable temperature solid state nuclear magnetic
resonance techniques. Using N-15 MAS and static NMR line shape
analysis, the disorder could be unambiguously ascribed to a
reorientational motion of the nitrite anion. A detailed
analysis of the line shapes revealed that at room temperature
the dynamic is characterized by a rapid pseudo-isotropic
reorientation of the NO2- group, in which the nitrogen atom
occupies the six possible orientations with equal probability.
The exchange process is not characterized by a continuous
decrease in the exchange frequency with decreasing temperature,
but has rather to be described by a dynamic order process. Upon
decreasing the temperature, one of the six possible split
positions for the nitrogen atom becomes increasingly favorable,
leading to a preferential occupation of the two nitrite
orientations related to this split position. Thus, the
transition from H-Na3ONO2 (isotropically reorienting nitrite
ions) to the M-phase is continuous and characterized by the
continuous order process of the nitrite ion.