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Efficient Calculation of the Negative Thermal Expansion in ZrW 2 O 8 .

Authors :
Vila FD
Hayashi ST
Rehr JJ
Source :
Frontiers in chemistry [Front Chem] 2018 Jul 30; Vol. 6, pp. 296. Date of Electronic Publication: 2018 Jul 30 (Print Publication: 2018).
Publication Year :
2018

Abstract

We present a study of the origin of the negative thermal expansion (NTE) on ZrW <subscript>2</subscript> O <subscript>8</subscript> by combining an efficient approach for computing the dynamical matrix with the Lanczos algorithm for generating the phonon density of states in the quasi-harmonic approximation. The simulations show that the NTE arises primarily from the motion of the O-sublattice, and in particular, from the transverse motion of the O atoms in the W-O and W-O-Zr bonds. In the low frequency range these combine to keep the WO <subscript>4</subscript> tetrahedra rigid and induce internal distortions in the ZrO <subscript>6</subscript> octahedra. The force constants associated with these distortions become stronger with expansion, resulting in negative Grüneisen parameters and NTE from the low frequency modes that dominate the positive contributions from the high frequency modes. This leads us to propose an anharmonic, two-frequency Einstein model that quantitatively captures the NTE behavior.

Details

Language :
English
ISSN :
2296-2646
Volume :
6
Database :
MEDLINE
Journal :
Frontiers in chemistry
Publication Type :
Academic Journal
Accession number :
30105223
Full Text :
https://doi.org/10.3389/fchem.2018.00296