Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile
- California Inst. of Technology (CalTech), Pasadena, CA (United States). Dept. of Applied Physics and Materials Science
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
Although the rutile structure of TiO2 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. In this paper, inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO2 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. Finally, 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.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Contributing Organization:
- California Inst. of Technology (CalTech), Pasadena, CA (United States)
- Grant/Contract Number:
- FG02-03ER46055
- OSTI ID:
- 1265627
- Alternate ID(s):
- OSTI ID: 1209761
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 92, Issue 5; ISSN 1098-0121
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Quantum Monte Carlo study of the energetics of the rutile, anatase, brookite, and columbite TiO$_{2}$ polymorphs
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text | January 2017 |
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