Universal phase diagram for the doped spin-Peierls system CuGeO3

We present a comparison of the effect of different dopants on both spin-Peierls and the Neel transition in CuGeO3. The composition dependence of the Neel-transition temperature TN can be scaled to a universal dependence for both in- and off-chain dopants taking into consideration the changes of the ionic radii. This suggests local distortions to play an important role for the effect of the doping. All in-chain dopants lead to a similar linear decrease of TSP; the slope differing only slightly within a factor of 1.5 for different dopands. The much weaker effect on TSP of the two off chain dopants Si and Ti scales to a common behaviour if the chemical pressure is taken into account. Furthermore, we found for in-chain dopants a clear correlation between the transition temperature TSP and the spin-Peierls gap.