Temperature evolution of structure and spatial organization of potassium nitrate embedded in mesoporous glasses

The temperature evolution of spatial organization and crystal structure of nanocomposite materials (NCM) based on porous glass with potassium nitrate (KNO₃) introduced from a saturated aqueous solution are studied using small-angle X-ray scattering and neutron diffraction methods on heating and cooling in the temperature range of 300–450 K. It is shown that the ferroelectric γ- phase in this NCM becomes predominant both upon heating and upon cooling. The phase diagram of potassium nitrate in NCM on cooling is established. The average size of coherent scattering region for the γ-phase is determined (< L > ∼ 100 Å), and it is practically independent of temperature. From the treatment of small- angle X-ray scattering data, the temperature dependence of the radius of gyration R_g is obtained. The average R_g value is 270(20) Å and does not depend on temperature on heating and cooling in the range RT – 450 K. On a spatial scale from 20 to 200 Å, potassium nitrate embedded in mesoporous glasses forms a developed surface fractal characterized by a Q^-α scattering law with α ∼ 3.52 in small-angle X-ray scattering. It is found that a significant part of potassium nitrate in the nanocomposite is in the amorphous phase.