Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion, and its stabilization of rutile TiO_2
Abstract
Although the rutile structure of TiO_2 is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000 K. Inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO_2 from 300 to 1373 K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizing the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of 3d electrons of Ti and 2p electrons of O atoms. With thermal expansion, the energy variation in this "phonon-tracked hybridization" flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.
Additional Information
© 2015 American Physical Society. Received 20 January 2015; revised manuscript received 29 April 2015; published 11 August 2015. Research at the SNS at the Oak Ridge National Laboratory was sponsored by the Scientific User Facilities Division, BES, DOE. This work was supported by the DOE Office of Science, Basic Energy Sciences, under Contract No. DEFG02-03ER46055.Attached Files
Published - PhysRevB.92.054304.pdf
Submitted - 1502.04667.pdf
Supplemental Material - TiO2-SM_BF.pdf
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Additional details
- Eprint ID
- 57404
- Resolver ID
- CaltechAUTHORS:20150511-083811430
- Department of Energy (DOE)
- DE-FG02-03ER46055
- Created
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2015-05-11Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field