Negative Thermal Expansion in the Polymorphic Modification of Double Sulfate β-AEu(SO) (A-Rb, Cs).

New polymorphic modifications of double sulfates β-AEu(SO) (A-Rb, Cs) were obtained by the hydrothermal method, the structure of which differs significantly from the monoclinic modifications obtained earlier by solid-state methods. According to single-crystal diffraction data, it was found that the compounds crystallize in the orthorhombic system, space group , with parameters β-RbEu(SO): = 9.4667(4) Å, = 13.

Temperature phase transitions in silver niobate and lithium tantalate-modified silver niobate ceramics.

The temperature behaviour of 0.955 AgNbO-0.045 LiTaO and AgNbO ceramics was studied in the range from 10 to 415 K using Raman spectroscopy.

The Effect of Interface Diffusion on Raman Spectra of Wurtzite Short-Period GaN/AlN Superlattices.

We present an extensive theoretical and experimental study to identify the effect on the Raman spectrum due to interface interdiffusion between GaN and AlN layers in short-period GaN/AlN superlattices (SLs). The Raman spectra for SLs with sharp interfaces and with different degree of interface diffusion are simulated by calculations and within the framework of the random-element isodisplacement model. The comparison of the results of theoretical calculations and experimental data obtained on PA MBE and MOVPE grown SLs, showed that the bands related to (LO) confined phonons are very sensitive to the degree of interface diffusion.

Phonons in Short-Period GaN/AlN Superlattices: Group-Theoretical Analysis, Calculations, and Raman Spectra.

We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established. calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses.

Structural, Electronic and Vibrational Properties of YAl(BO).

The crystal structure of YAl(BO) is obtained by Rietveld refinement analysis in the present study. The dynamical properties are studied both theoretically and experimentally. The experimental Raman and Infrared spectra are interpreted using the results of calculations within density functional theory.