Structure and Dynamics of a Lattice of Tetragonal Germanates R2Ge2O7 (R = Tb-Lu, Y): Ab Initio Calculation

TL;DR

This study uses ab initio density functional theory to analyze the structure, vibrational spectra, and elastic properties of rare-earth germanates R2Ge2O7, providing new insights into their phonon modes and IR/Raman spectra.

Contribution

First ab initio calculations of the entire series of R2Ge2O7 germanates, including structural, vibrational, and elastic properties, filling gaps in experimental data.

Findings

Determined phonon spectra and vibrational modes for R2Ge2O7 series.

Interpreted IR and Raman spectra, especially for yttrium germanate.

Provided elastic constants and structural insights for rare-earth germanates.

Abstract

The crystal structure, phonon spectrum, and elastic constants of a series of rare-earth germanates (including yttrium germanate R2Ge2O7 (R = Tb-Lu, Y)) with a tetragonal structure have been ab initio calculated within the density functional theory. The frequencies and types of fundamental vibrations and the intensities of IR and Raman modes are determined. The degrees of participation of ions in each mode are determined by analyzing the displacement vectors obtained as a result of the ab initio calculations. The calculations have been performed for the first time; there are no corresponding experimental data for the entire series of compounds (except for the IR and Raman spectra of yttrium germanate). The performed calculations made it possible to interpret and supplement the known data in the literature on IR and Raman spectra of yttrium germanate Y2Ge2O7.