Effect of high hydrostatic pressure on the phonon modes of Tb3Al5O12 and Dy3Al5O12 single crystals

In the present work we study the effect of high hydrostatic pressure on the Raman spectrum of Tb3Al5O12 (up to 26 GPa) and Dy3Al5O12 (up to 16 GPa) si ngle crystals. Group theory predicts 25 Raman active modes for these compou nds, while experimentally we observe only 13 Raman peaks for Tb3Al5O12 and 16 for Dy3Al5O12. The pressure coefficient of the Raman modes of Tb3Al5O12 are systematically smaller than those for the Dy3Al5O12. We did not observe , by Raman spectroscopy any kind of phase transition as well as hysteresis phenomena in the pressure region under investigation. (C) 1999 Published by Elsevier Science B.V. All rights reserved.