First-principles mode Gruneisen parameters and negative thermal expansion in α-ZrW2O8
V Gava1, A L Martinotto, C A Perottoni
1Instituto de Materiais Cerâmicos, Universidade de Caxias do Sul, 95765-000 Bom Princípio-Rio Grande do Sul, Brazil.
Physical Review Letters
|December 11, 2012
Summary
Negative thermal expansion in alpha-zirconium tungstate (α-ZrW(2)O(8)) at low temperatures is primarily driven by specific low-energy optic modes. Other optic modes contribute significantly to thermal expansion near room temperature.
Area of Science:
- Materials Science
- Solid State Physics
- Computational Materials Science
Background:
- Negative thermal expansion (NTE) is a counterintuitive property observed in certain materials.
- Understanding the lattice dynamics responsible for NTE is crucial for designing advanced materials.
Purpose of the Study:
- To investigate the lattice dynamics of alpha-zirconium tungstate (α-ZrW(2)O(8)) using theoretical calculations.
- To determine the primary vibrational modes responsible for negative thermal expansion in α-ZrW(2)O(8) across different temperature ranges.
- To correlate theoretical findings with experimental spectroscopic data.
Main Methods:
- Density functional theory (DFT) calculations to estimate Mode Grüneisen parameters for zone-center modes.
- Application of the Debye-Einstein model within the quasiharmonic approximation to obtain the temperature dependence of the coefficient of thermal expansion.
- Far-infrared spectroscopy to experimentally identify low-energy optic modes.
Main Results:
- Identified lowest energy optic modes at 45 and 46 cm⁻¹ as key contributors to low-temperature NTE.
- Experimental confirmation of a triply degenerated infrared active optic mode in the far-infrared spectrum.
- Demonstrated that additional optic modes with energies below 25 meV significantly influence thermal expansion near room temperature.
Conclusions:
- The study elucidates the specific vibrational modes driving the negative thermal expansion behavior of α-ZrW(2)O(8).
- Findings provide insights into the mechanisms of NTE in open framework materials, supporting existing theoretical models.
- Combines theoretical and experimental approaches to offer a comprehensive understanding of α-ZrW(2)O(8) thermal expansion.
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