Anisotropic phonon density of states: the application of Rietveld and Mössbauer texture analysis in aligned powders

Since it is not always feasible to synthesize single crystals of novel materials, the orientation of layered polycrystals has become an attractive basis for studying the angular dependence of inelastic scattering of X-rays or neutrons. Utilizing Rietveld analysis, the anisotropic properties of layered structures in novel manganites and cuprates have been studied with oriented powders instead of single crystals. The phonon density of states (DOS) and atomic thermal displacement are anisotropic in the A-site-ordered manganites LnBaMn₂O_y for the series y = 5 and y = 6 (Ln = Y, La, Sm and Gd). This article establishes the angular dependence of the DOS on texture of arbitrary strength, links the textures observed by X-ray and γ-ray techniques, and solves the problem of disentanglement of the Goldanskii–Karyagin effect and texture in Mössbauer spectra.