Folded phonon mode observed by Raman scattering in Zn- and Si-doped CuGeO3

We have studied Zn- and Si-doping effects on the 366-cm(-1) folded phonon i n the spin-Peierls (SP) systems Cu1-xZnxGeO3 and CuGe1-ySixO3 by means of R aman scattering. The folded phonon is induced by the formation of the super lattice. The Raman intensity at 6 K decreases almost linearly with increasi ng dopant concentration. The temperature dependence of Raman intensity and the broad line shape in the x = 0.021 Zn-doped crystal indicate that the SP long-range order is not formed in this sample. In the low-temperature anti ferromagnetic (AF) phases in lightly doped crystals, we observe the sharp f olded phonon mode, indicating that the lattice dimerization persists in thi s phase. No sharp Raman line from the folded phonon is observed in the AF p hase of the x = 0.021 Zn- and y = 0.04 Si-doped crystals, indicating the ex istence of the uniform AF phase in these samples.