Ferroelectricity and gradual melting in NaNO₂ particles confined within porous alumina

NMR and dielectric studies were carried out for ferroelectric NaNO₂ embedded into porous alumina. ²³Na spin-lattice relaxation and static lineshape were measured within a large temperature range covering the ferroelectric phase transition in bulk sodium nitrite till NaNO₂ melting. The coexistence of the crystalline and melted states of confined sodium nitrite was observed above 400 K, gradual melting being over at about 510 K. The solid portion of confined sodium nitrite bore ferroelectricity with phase transition temperature higher than that in bulk NaNO₂. Correlation time of molecular mobility in the melted fraction was found and activation enthalpy was estimated.