Phase transitions in K1-xNaxNO3 embedded into molecular sieves

Dielectric studies of molecular sieves MCM-41 filled with K1-xNaxNO3 salts (x = 0, 0.05 and 0.10) were carried out and compared with results obtained for their bulk counterparts. The regular increase upon warming of the temperature of the reconstructive phase transition from phase II to phase I with decreasing pore sizes was observed for all x. A thermodynamic model for shifts of reconstructive phase transitions was suggested. Ferroelectric phase III was shown to occur upon cooling in bulk binary salts and for all x in confined geometry under the thermal conditions when phase III does not arise in bulk KNO3. Ferroelectricity persisted below room temperature in the bulk binary salt with x = 0.10.