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

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.

Temperature-dependent Raman and x-ray studies of the spin-ice pyrochloreDy2Ti2O7and nonmagnetic pyrochlore

“…We note that Lummen et al [16] and Maczka et al [17] also see this "new" mode in their low-temperature Raman spectra of Dy 2 T i 2 O 7 . Lummen et al tentatively assigned the "new" mode near 300 cm −1 to the first excited CF level after the crystal field splitting estimation due to Rosenkranz et al [28].…”

“…It is suggested in ref. [17] that the anomalous temperature dependence could arise from anharmonic interactions. In order to understand the anomalous temperature dependence of phonon modes, we have done detailed Raman studies on single crystals of Dy 2 T i 2 O 7 and its non-magnetic analogue Lu 2 T i 2 O 7 over a temperature range of 12 to 300 K. A quantitative comparison of the phonons of these two pyrochlores is done to understand the role of spin-phonon coupling in giving rise to the anomalous phonon behaviors.…”

Phonon and crystal field excitations in geometrically frustrated rare earth titanates

“…Recently, some additional indications of low-temperature structural changes in the rare earth titanates have been found both experimentally 78 and theoretically. 79 …”

Raman study of phonon modes in bismuth pyrochlores

“…The appearance of the additional Raman bands, which correspond to Raman-inactive modes of the ideal pyrochlore structure, confirms the displacive disorder of the A and OЈ sites in the bismuth pyrochlores. The Raman modes were assigned by reference to the Raman spectra of many other pyrochlores, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] some of which include lattice-dynamical calculations, 12,27,28 and firstprinciples calculations. 11 In the literature, the lattice dynamical and ab initio calculations show an interesting difference.…”

“…Each mode was studied and assigned by first referencing the literature on diverse samples with structures close to the ideal pyrochlore structure. 10,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Then, the bands were also compared to our ab initio calculations for Bi 2 Ti 2 O 7 and those in the literature for Cd 2 Nb 2 O 7 . 11 Table II shows the frequencies of the various observed modes for the four samples along with their assignment.…”