DOPING EFFECTS ON THE FOLDED PHONON MODE IN THE SPIN-PEIERLS SYSTEMS CUGEO3 AND ALPHA'-NAV2O5

We have studied the Zn- and Si-doping effects on the 368 cm(-1) folded phonon in CuGeO3 by means of Raman scattering. With increasing dopant concentrations, the transition temperature decreases to a constant va lue, and the lattice distortion at T = 0 also decreases. In the doped samples, a bread Raman peak of the folded phonon still remains observa ble even above the transition temperature, indicating the increase of the short-range fluctuations of lattice dimerization. In alpha'-NaV2O5 , we have observed a folded phonon at 948 cm(-1) in the spin-Peierls p hase. The defect of the Na+ ions also causes the decrease of the inten sity and the increase of the half-width of the folded phonon. (C) 1998 Elsevier Science B.V. All rights reserved.