Local vibrations and negative thermal expansion in ZrW2O8
F Bridges1, T Keiber1, P Juhas2
1Department of Physics, University of California, Santa Cruz, California 95064, USA.
Physical Review Letters
|March 4, 2014
Summary
The study reveals the Zr-O-W linkage in ZrW2O8 is stiff, not flexible. This stiffness, driven by specific atomic rotations, explains the material's negative thermal expansion.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- Negative thermal expansion (NTE) materials exhibit unique properties.
- Understanding the atomic mechanisms behind NTE is crucial for material design.
- Zirconium tungstate (ZrW2O8) is a prominent NTE material.
Purpose of the Study:
- To investigate the stiffness of the Zr-O-W linkage in ZrW2O8.
- To elucidate the vibrational modes responsible for negative thermal expansion in ZrW2O8.
- To correlate structural dynamics with macroscopic thermal properties.
Main Methods:
- X-ray Pair Distribution Function (XPDF) analysis from 10-500 K.
- Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy.
- Analysis focused on interatomic correlations (Zr-Zr, W-W, Zr-O, W-O).
Main Results:
- XPDF data is highly sensitive to W-Zr and W-W correlations.
- The Zr-W peak shows weak temperature dependence, indicating a stiff Zr-O-W linkage.
- Low-energy vibrational modes involve correlated rotations of ZrO6 octahedra and WO4 tetrahedra, not flexible O atom motion.
Conclusions:
- The Zr-O-W linkage in ZrW2O8 is relatively stiff and does not allow bending.
- Negative thermal expansion is attributed to correlated rotations of polyhedra, leading to specific atomic translations.
- This provides a detailed microscopic explanation for the NTE behavior of ZrW2O8.
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