Structure and properties of confined sodium nitrite
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
Published online: 5 November 2003
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.
PACS: codes. – 77.84.Lf - Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials / codes. – 61.43.Gt - Powder, porous materials / codes. – 61.12.Ld - Neutron diffraction
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2003