Alexandra Franz

Phase transitions in nanostructured potassium nitrate

Dielectric properties and temperature evolution of the crystal structure of nanocomposites on the basis of porous glasses and KNO3 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 KNO3 and porous glasses with the average pore diameters of 7 nm, the ferroelectric phase becomes stable down to 100 K after the first heating–cooling circle.

Neutron and X-ray Diffraction Studies of KNO3 Embedded into Porous Glasses

Temperature evolution of crystal structure of KNO3 embedded into porous glasses with average pore diameters 7 nm, 46 nm and 320 nm have been studied by neutron and X-rays diffraction. For 320 nm samples it is shown that KNO3 phase transition temperatures and their sequence corresponds to the bulk. For 46 nm sample the temperature interval of the ferroelectric phase stability enlarges significantly and there is a temperature range where all three phases coexist. It has been demonstrated that for 7 nm samples ferroelectric phase becomes stable down to 100°K and remains stable after consequent heating-cooling cycles.