Critical phenomena at the spin-Peierls transition in doped CuGeO3

We have examined the critical properties of several lightly doped samples of CuGeO3 through x-ray diffraction measurements of the order parameter. We obtain an exponent β consistent with that obtained for pure CuGeO3, where β=0.345±0.03, for 0.1% Zn-doped, 0.2% Si-doped, and 0.4% Si-doped samples. Measurements on two 0.1% Cd-doped samples produce results clearly inconsistent with those for the pure compound and well described by mean field …