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Pressure-induced ferroelastic phase transition in SnO2 from density functional theory
Lei Yang1, Weiliu Fan2, Yanlu Li3
1State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, People's Republic of China.
The Journal of Chemical Physics
|May 3, 2014
Summary
High-pressure tin dioxide (SnO2) undergoes a ferroelastic transition. Density functional theory and Landau theory reveal how B1g mode softening and its coupling with transverse acoustic modes drive this transformation.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Computational Chemistry
Background:
- Tin dioxide (SnO2) exhibits a rutile structure.
- Understanding high-pressure phase transitions is crucial for materials science.
Purpose of the Study:
- Investigate the high-pressure ferroelastic transition of SnO2 from rutile to CaCl2-type structure.
- Clarify the softening mechanism of the B1g mode and its coupling with the transverse acoustic (TA) mode.
Main Methods:
- Density Functional Theory (DFT) calculations.
- Landau free energy theory.
- Analysis of Landau energy maps.
Main Results:
- The B1g mode (order parameter Q) softens due to Sn-O-Sn bond bending.
- Coupling between the soft B1g mode and the soft TA mode (strain ɛ) minimizes octahedral distortion.
- Landau Gibbs free energy is decomposed into contributions from bond stretching, bending, and octahedral distortion.
Conclusions:
- The ferroelastic transition in SnO2 is driven by coupled lattice dynamics.
- DFT and Landau theory provide a robust framework for understanding pressure-induced phase transitions.
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