Lattice dynamics of coesite

TL;DR

This study combines experimental and computational methods to analyze the lattice dynamics of coesite, revealing detailed vibrational properties, stability features, and comparisons with alpha-quartz.

Contribution

It provides a comprehensive harmonic lattice dynamics analysis of coesite using combined diffuse and inelastic x-ray scattering with ab initio calculations, offering new insights into its vibrational behavior.

Findings

Identification of a critical point at the zone boundary affecting vibrational density of states

Comparison reveals similarities and differences with alpha-quartz in low-energy vibrational properties

Experimental validation of lattice dynamics calculations enhances understanding of crystalline stability

Abstract

The lattice dynamics of coesite has been studied by a combination of diffuse x-ray scattering, inelastic x-ray scattering and an ab initio lattice dynamics calculation. The combined technique gives access to the full lattice dynamics in harmonic description and thus eventually provides detailed information on the elastic properties, the stability and metastability of crystalline systems. The experimentally validated calculation was used for the investigation of eigenvectors, mode character and their influence on the density of vibrational states. High symmetry sections of the reciprocal space distribution of diffuse scattering and inelastic x-ray scattering spectra as well as the density of vibrational states and the dispersion relation are reported and compared to the calculation. A critical point at the zone boundary is found to contribute strongly to the main peak of the low energy part in the density of vibrational states. Comparison with the most abundant SiO2 polymorph - alpha-quartz - reveals similarities and distinct differences in the low-energy vibrational properties.