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Raman study of phonon modes in bismuth pyrochlores

2010; American Physical Society; Volume: 82; Issue: 21 Linguagem: Inglês

10.1103/physrevb.82.214302

1550-235X

Daniel J. Arenas, L. V. Gasparov, Wei Qiu, Juan C. Nino, Charles H. Patterson, D. B. Tanner,

Nuclear Materials and Properties

The Raman spectra of the cubic bismuth pyrochlores ${\text{Bi}}_{3/2}{\text{Zn}}_{0.92}{\text{Nb}}_{3/2}{\text{O}}_{6.92}$, ${\text{Bi}}_{3/2}{\text{ZnTa}}_{3/2}{\text{O}}_{7}$, ${\text{Bi}}_{3/2}{\text{MgNb}}_{3/2}{\text{O}}_{7}$, and ${\text{Bi}}_{3/2}{\text{MgTa}}_{3/2}{\text{O}}_{7}$ have been measured at room temperature. The frequencies of the Raman modes, obtained from first-principles calculations, for ${\text{Bi}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ are presented for comparison. The spectra of the four samples are similar and agree well with the first-principles calculations. Each bismuth pyrochlore shows more than the six modes expected for the ideal pyrochlore structure. The analysis shows that many of the additional modes could be explained as the relaxation of the selection rules due to the displacive disorder. The Raman modes are assigned by reference to spectra of other pyrochlore materials, comparison to infrared data, and the ab initio calculations.