Journal
JOURNAL OF RAMAN SPECTROSCOPY
Volume 43, Issue 4, Pages 549-555Publisher
WILEY-BLACKWELL
DOI: 10.1002/jrs.3058
Keywords
geometrically frustrated pyrochlore; phonon anharmonicity; Raman spectroscopy; crystal field transition
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Funding
- Indo-French Centre for Promotion of Advanced Research (IFCPAR) [3108-1]
- Department of Science and Technology (DST), India
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Anomalous temperature dependence of Raman phonon wavenumbers attributed to phononphonon anharmonic interactions has been studied in two different families of pyrochlore titanates. We bring out the role of the ionic size of titanium and the inherent vacancies of pyrochlore in these anomalies by studying the effect of replacement of Ti4?+ by Zr4?+ in Sm2Ti2O7 and by stuffing Ho3?+ in place of Ti4?+ in Ho2Ti2O7 with appropriate oxygen stoichiometry. Our results show that an increase in the concentration of the larger ion, i.e. Zr4?+ or Ho3?+, reduces the phonon anomalies, thus implying a decrease in the phononphonon anharmonic interactions. In addition, we find signatures of coupling between a phonon and crystal field transition in Sm2Ti2O7, manifested as an unusual increase in the phonon intensity with increasing temperature. Copyright (c) 2011 John Wiley & Sons, Ltd.
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