Pergamon Solid State Communications, Vol. 93, No. 9, 729-732, 1995 pp. Copyright 0 1995. Elsevier Science Ltd zyxwvuts Printed in Great Britain. All rights reserved 003x- 109x(94)00848-5 0038-1098/;5 $Y.50+.00 BRILLOUIN SCATTERING IN CUBIC PHASE OF YTTRIUM SESQUIOXIDE. C. Proust’, Y VailIs*, Y. Luspin* E. Husson’ l- Laboratoire de Physique et Mecanique des Materiaux, ESEM, Universite d’orleans et CRPHT-CNRS, 45071 Orleans cedex 2, France. 2- CRPHT-CNRS, 4507 1 Orleans cedex 2, France (Received 11 October 1994, accepted for publication 16 November 1994 by G.Bastard) A Brillouin scattering investigation has been performed in a YrOs single crystal, from room temperature up to 470 K. Elastic constant Crr and linear combination [(Crr + Cr2)/2 + CM] were measured and the Cl2 and CM constants roughly estimated. The results are discussed in comparison with those obtained with zyxwvutsrqponmlkjihgfedcbaZYXWVUTS a Alz0~. Keywords : D. Elasticity, E. Elastic light scattering Introduction Yttrium sesquioxide is a highly refractory material which exhibits promising properties in several technological areas such as electronics, optics, mechanics... [l-3]. The crystal structure was studied by X-ray diffraction [4, 51 and by neutron diffraction [6, 71. Yr0~ crystallizes in the bixbyite structure of the cubic system at room temperature. Several infrared and Raman studies have been published [S-l 21 but to our knowledge, no work about the elastic properties of YzO, has been published yet. This may be due to the difficulty to obtain high purity single crystals with a good optical quality, because the melting point (T=2680 K) is extremely high and that, during the cooling, the crystal is subject to important internal stress and to a phase transition between the high- temperature hexagonal phase and the cubic one at about 2570 K [13]. The present work reports a Brillouin scattering investigation of the elastic constants on an YzOj single crystal at room temperature and shows the evolution of these constants over a temperature range 290-690 K. Experimental Single crystals of Y203 were grown by the flame fusion method (Vemeuil process) described elsewhere [ 141. All the crystals obtained exhibit defects in the form of cleavage planes corresponding to the (111) planes of the cubic phase. However, these crystals were of suitable quality to record Raman polarized spectra [ 121. A single crystal was oriented by the Laue method and cut in the form of a small cube of 5 mm edge, with faces parallel to (100) (010) and (001) crystallographic planes. Then the sample was optically polished with a diamond paste. The spectrometer is a pressure scanned triple-passed plane Fabry-Perot interferometer (effective finesse 70, resolving power 760 000 ) which is frequency checked by a Michelson in tandem. The light source is the line h, = 5 14.5 nm of a single mode Ar-ion laser. We used the right angle scattering geometry. The measured Brillouin line shifts VI. and VT corresponding to the longitudinal (L) and transverse (T) acoustic waves permitted to calculate their velocities VL and VT by : VI, = v&In & and VT = v&In fi where n is the refractive index at ho. The n value was estimated to 1.935 for a wavelength of 5 14.5 nm from the Nigara’s works [ 151 about the evolution of n versus wavelength at 293 K.