Suppression of the commensurate spin-Peierls state in Sc-doped Ti1−xScxOCl (x=0.0, 0.01, and 0.03)

We have performed x-ray scattering measurements on single crystals of the doped spin-Peierls compound Ti1−xScxOCl (x=0,0.01,0.03). These measurements reveal that the presence of nonmagnetic dopants has a profound effect on the unconventional spin-Peierls behavior of this system, even at concentrations as low as 1%. Sc doping suppresses commensurate fluctuations in the pseudogap and incommensurate spin-Peierls phases of TiOCl and prevents the formation of a long-range ordered spin-Peierls state. Broad incommensurate scattering develops in the doped compounds near Tc2∼93 K and persists down to base temperature (∼7 K) with no evidence of a lock-in transition. The width of the incommensurate dimerization peaks indicates short correlation lengths on the order of ∼12 Å below Tc2. The intensity of the incommensurate scattering is significantly reduced at higher Sc concentrations, indicating that the size of the associated lattice displacement decreases rapidly as a function of doping.