Phonon anomalies and structural transition in spin ice Dy2Ti2O7: a simultaneous pressure‐dependent and temperature‐dependent Raman study (original) (raw)

We revisit the assignment of Raman phonons of rare-earth titanates by performing Raman measurements on single crystals of O 18 isotope-rich spin ice Dy 2 Ti 2 O 18 7 and nonmagnetic Lu 2 Ti 2 O 18 7 pyrochlores and compare the results with their O 16 counterparts. We show that the low-wavenumber Raman modes below 250 cm À1 are not due to oxygen vibrations. A mode near 200 cm À1 , commonly assigned as F 2g phonon, which shows highly anomalous temperature dependence, is now assigned to a disorderinduced Raman active mode involving Ti 4+ vibrations. Moreover, we address here the origin of the 'new' Raman mode, observed below T C~1 10 K in Dy 2 Ti 2 O 7 , through a simultaneous pressure-dependent and temperature-dependent Raman study. Our study confirms the 'new' mode to be a phonon mode. We find that dT C /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.