Dielectric properties and temperature evolution of the crystal structure of nanocomposites on the basis of porous glasses and KNO 3 embedded into the pores have been studied on heating and cooling. It is shown that the stability of the ferroelectric phase depends on nanoparticle sizes and temperature prehistory of sample preparation and measurement procedure. The temperature interval, where the ferroelectric phase exists, increases on decreasing of the nanoparticle size. In the composite of KNO 3 and porous glasses with the average pore diameters of 7 nm, the ferroelectric phase becomes stable down to 100 K after the first heatingÀcooling circle. IntroductionAt room temperature (RT) the bulk potassium nitrate (KNO 3 ) has the orthorhombic structure Pmnc (a-phase or phase II). At 403 K a reconstructive phase transition (PT) from the low-temperature paraelectric phase to the high-temperature paraelectric trigonal phase R 3 m (b-phase, phase I) occurs. On cooling from this b-phase KNO 3 transforms to another trigonal phase R 3 m (g-phase) at the temperature »397 K. This g-phase is ferroelectric and remains stable on cooling down to 378 K and below this temperature a transformation into the initial a-phase takes place. For thin films and ultradispersed particles, the situation changes essentially. For example, in paper [1] it has been shown that KNO 3 thin films exhibit ferroelectric properties at temperatures even below 273 K possibly due to different thermal expansion of film and substrate. Later on, similar changes in the g ! a PT temperature have been observed for KNO 3 powders and it was attributed to cooperative behavior. [2] It has been demonstrated [3] that thin films have address voltages between 2 and 6 V, depending on the thickness, switching times as fast as 20 ns and square hysteresis loops. It opens a possibility to use KNO 3 thin films as materials for production of non-volatile ferroelectric random access memory (FeRAM). [4] As for nanocomposite materials (NCMs) with KNO 3 , the studies [5À9] carried out for NCM on the basis of mesoporous molecular sieves MCM-41,[10] having an ordered

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