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Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion, and its stabilization of rutile TiO_2

Lan, Tian and Li, C. W. and Hellman, O. and Kim, D. S. and Muñoz, J. A. and Smith, H. and Abernathy, D. L. and Fultz, B. (2015) Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion, and its stabilization of rutile TiO_2. Physical Review B, 92 (5). Art. No. 054304. ISSN 1098-0121.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle Material
Li, C. W.0000-0002-0758-5334
Hellman, O.0000-0002-3453-2975
Kim, D. S.0000-0002-5707-2609
Abernathy, D. L.0000-0002-3533-003X
Fultz, B.0000-0002-6364-8782
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.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-03ER46055
Issue or Number:5
Classification Code:PACS number(s): 63.20.Ry, 65.40.−b, 78.70.Nx
Record Number:CaltechAUTHORS:20150511-083811430
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57404
Deposited By: Tony Diaz
Deposited On:11 May 2015 17:58
Last Modified:03 Oct 2019 08:24

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