Calorimetry of matrix-isolated sodium nitrite NaNO$_{2}$

Differential scanning calorimetry has been used to carry out a high-precision study of sodium nitrite NaNO$_{2}$ incorporated into different silicate nanoporous matrices. Heat-capacity maxima due to smeared ferroelectric phase transitions have been discovered. Characteristics (intensity, half-width, phase-transition temperature, etc.) of the maxima have been investigated. Heat-capacity maxima related to an incommensurable phase transition have been reliably identified. The maxima can be attributed to the formation of appropriate orientation of sodium-nitrite nanocrystals in matrix pores.