Determination of the Landau–Placzek Ratio from Small-Angle X-ray Scattering Data

Abstract

The possibility of determining the Landau–Placzek ratio RLP by the small-angle X-ray scattering (SAXS) technique is discussed. The intensities of small-angle X-ray scattering by thermal density fluctuations, concentration fluctuations, and a microinhomogeneous structure, as well as the phonon and structural components of scattering by thermal density fluctuations, can be separated from the angular and temperature dependences of the SAXS intensity. This makes it possible to determine the Landau–Placzek ratio RLP as the ratio between the structural and phonon components of the intensity of scattering by thermal density fluctuations. Within the limits of experimental error, the calculated temperature dependence of the Landau–Placzek ratio RLP for vitreous boron oxide coincides with the curve obtained from the light scattering data. It is found that the temperature coefficient of the SAXS intensity (phonon component) for boron oxide changes at the temperature of the transition from a supercooled liquid state to a solid noncrystalline state. This suggests a similarity of this transition to second-order phase transitions.