Eur. Phys. J. E (2003) 12: 21-24
https://doi.org/10.1140/epjed/e2003-01-006-4

Structure and properties of confined sodium nitrite

¹ Ioffe Physico-Technical Institute, 26 Politekhnicheskaya, 194021, St.-Petersburg, Russia
² Institute Laue Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France

Received: 1 January 2003
Published online: 5 November 2003

Abstract

The temperature evolution of the structure of NaNO₂ nanocomposite ferroelectric material in a porous glass with 7 nm pores was studied by neutron diffraction in temperature region from room temperature up to the melting, i.e. in the ferro- and paraelectric phases. It is demonstrated that in the ferroelectric phase the structure is consistent with the structure of the bulk, but above the ferroelectric phase transition (and up to ≈ 513 K) a volume premelted state is formed, manifesting itself in a growth of amplitudes of ion thermal vibrations, a steep increase of elementary cell volume and “softening” of lattice. For the first time the temperature dependence of order parameter η for confined sodium nitrite is determined. η (T) follows a power law with T _C =425.6± 2.1 K and β= 0.31± 0.04, which is essentially different from that for bulk NaNO₂. Our obtained data are in a good agreement with the results of earlier dielectric and neutron diffraction measurements.