Abstract: | We revisit the assignment of Raman phonons of rare‐earth titanates by performing Raman measurements on single crystals of O18 isotope‐rich spin ice and nonmagnetic pyrochlores and compare the results with their O16 counterparts. We show that the low‐wavenumber Raman modes below 250 cm−1 are not due to oxygen vibrations. A mode near 200 cm−1, commonly assigned as F2g phonon, which shows highly anomalous temperature dependence, is now assigned to a disorder‐induced Raman active mode involving Ti4+ vibrations. Moreover, we address here the origin of the ‘new’ Raman mode, observed below TC ~ 110 K in Dy2Ti2O7, through a simultaneous pressure‐dependent and temperature‐dependent Raman study. Our study confirms the ‘new’ mode to be a phonon mode. We find that dTC/dP = + 5.9 K/GPa. Temperature dependence of other phonons has also been studied at various pressures up to ~8 GPa. We find that pressure suppresses the anomalous temperature dependence. The role of the inherent vacant sites present in the pyrochlore structure in the anomalous temperature dependence is also discussed. Copyright © 2012 John Wiley & Sons, Ltd. |