Temperature‐dependent Raman scattering studies of the geometrically frustrated pyrochlores Dy₂Ti₂O₇, Gd₂Ti₂O₇ and Er₂Ti₂O₇

Abstract

Abstract The temperature‐dependent Raman studies of A 2 Ti 2 O 7 (A = Dy, Er, Gd) were performed on single crystals and polycrystalline samples in the 4.2–295 K temperature range. The Raman spectra showed softening of the majority of phonon modes upon cooling in the whole temperature range studied and large decrease of linewidths. These changes have been analyzed in terms of strong third‐order phonon–phonon anharmonic interactions. Moreover, the 312 and 330 cm −1 modes of Er 2 Ti 2 O 7 (Gd 2 Ti 2 O 7 ) showed hardening upon cooling down to about 130 K (100 K) and then anomalous softening below this temperature. The observed anomalous behavior of the Raman modes indicates that some important changes occur in these materials at low temperatures. However, the origin of this behavior is still not clear. Copyright © 2008 John Wiley & Sons, Ltd.