Doping effects on the folded phonon mode in the spin-Peierls systems CuGeO3 and α′-NaV2O5

We have studied the Zn- and Si-doping effects on the 368 cm −1 folded phonon in CuGeO 3 by means of Raman scattering. With increasing dopant concentrations, the transition temperature decreases to a constant value, and the lattice distortion at T = 0 also decreases. In the doped samples, a broad Raman peak of the folded phonon still remains observable even above the transition temperature, indicating the increase of the short-range fluctuations of lattice dimerization. In α′ -NaV 2 O 5 , we have observed a folded phonon at 948 cm −1 in the spin-Peierls phase. The defect of the Na + ions also causes the decrease of the intensity and the increase of the half-width of the folded phonon.