Anisotropic phonon DOS: the application of Rietveld and Mossbauer texture analysis in aligned powders

TL;DR

This paper develops a method to analyze anisotropic phonon densities and atomic displacements in oriented powders of layered materials, using Rietveld and Mossbauer texture analysis, to study their directional properties without single crystals.

Contribution

It introduces a novel approach combining Rietveld and Mossbauer techniques to analyze anisotropic phonon DOS and texture effects in layered polycrystalline materials.

Findings

Established angular dependence of phonon DOS on texture

Linked textures observed by x-ray and gamma-ray techniques

Disentangled Goldanskii-Karyagin effect from texture in Mossbauer spectra

Abstract

While synthesizing the single crystals of novel materials is not always feasible, orienting the layered polycrystals becomes an attractive method in the studies of angular dependencies of inelastic scattering of x-rays or neutrons. Putting in use the Rietveld analysis of layered structures in novel manganites and cuprates we develop the studies of their anisotropic properties with oriented powders instead of single crystals. Densities of phonon states (DOS) and atomic thermal displacememts (ATD) are anisotropic in the A-site ordered manganites LnBaMn2Oy of both y=5 and y=6 series (Ln=Y, La, Sm, Gd). We establish the angular dependence of DOS on textures of arbitrary strengths, link the textures observed by x-ray and gamma-ray techniques, and solve the problem of disentanglement of Goldanskii-Karyagin effect (GKE) and texture in Moessbauer spectra.