Temperature Evolution of Sodium Nitrite Structure in a Restricted Geometry

TL;DR

This study investigates the temperature-dependent crystal structure of sodium nitrite in a nanocomposite form within porous glass, revealing a transition to a 'premelted state' characterized by large thermal vibrations above the ferroelectric transition.

Contribution

First detailed neutron diffraction analysis of sodium nitrite in a porous matrix across ferroelectric and paraelectric phases, identifying structural changes and thermal vibration behavior.

Findings

Structural consistency with bulk in ferroelectric phase

Observation of giant thermal vibrations above transition

Identification of a 'premelted state' in nanocomposite

Abstract

The NaNO$_{2}$ nanocomposite ferroelectric material in porous glass was studied by neutron diffraction. For the first time the details of the crystal structure including positions and anisotropic thermal parameters were determined for the solid material, embedded in a porous matrix, in ferro- and paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with bulk data but above transition temperature the giant growth of amplitudes of thermal vibrations is observed, resulting in the formation of a "premelted state". Such a conclusion is in a good agreement with the results of dielectric measurements published earlier.