Phonon mechanism for the negative thermal expansion of zirconium tungstate, ZrW2O8

Abstract

Negative thermal expansion (NTE) in ZrW₂O₈ was investigated using a flexibility analysis of ab initio phonons. It was shown that no previously proposed mechanism adequately describes the atomic-scale origin of NTE in this material. Instead it was found that the NTE in ZrW₂O₈ is driven, not by a single mechanism, but by wide bands of phonons that resemble vibrations of near-rigid WO₄ units and Zr–O bonds at low frequency, with deformation of O–W–O and O–Zr–O bond angles steadily increasing with increasing NTE-phonon frequency. It is asserted that this phenomenon is likely to provide a more accurate explanation for NTE in many complex systems not yet studied.