Unusual Low-Energy Phonon Dynamics in the Negative Thermal Expansion Compound ZrW2O8

TL;DR

This study investigates the unusual low-energy phonon behavior in ZrW2O8, revealing exotic lattice dynamics linked to its negative thermal expansion through infrared spectroscopy and theoretical calculations.

Contribution

It provides new insights into the low-energy phonon modes and their connection to negative thermal expansion in ZrW2O8, highlighting the role of its underconstrained structure.

Findings

Infrared active phonons at low energy show unusual temperature dependence.

Eigenvector calculations reveal mixing of librational and translational motions.

The low-energy lattice dynamics are linked to the material's negative thermal expansion.

Abstract

An infrared study of the phonon spectra of ZrW2O8 as a function of temperature which includes the low energy (2-10 meV) region relevant to negative thermal expansion is reported and discussed in the context of specific heat and neutron density of states results. The prevalence of infrared active phonons at low energy and their observed temperature dependence are highly unusual and indicative of exotic low-energy lattice dynamics. Eigenvector calculations indicate a mixing of librational and translational motion within each low-frequency IR mode. The role of the underconstrained structure in establishing the nature of these modes, and the relationship between the IR spectra and the large negative thermal expansion in ZrW2O8 are discussed.