Comment on "X-ray resonant scattering studies of orbital and charge ordering in Pr1-xCaxMnO3" -: art. no. 127101

In a recently published paper [Phys. Rev. B 64, 195133 (2001)], Zimmermann present a systematic x-ray scattering study of charge and orbital ordering phenomena in the Pr1-xCaxMnO3 series with x=0.25, 0.4, and 0.5. They propose that for Ca concentrations x=0.4 and 0.5, the appearance of (0,k+1/2,0) reflections are originated by the orbital ordering of the e(g) electrons in the a-b plane while the (0,2k+1,0) reflections are due to the charge ordering among the Mn3+ and Mn4+ ions. Moreover, for small Ca concentrations (x<0.3), only the orbital ordering is considered and it occurs at (0,k,0) reflections. A rigorous analysis of all these resonance reflections will show the inadequacy of the charge-orbital model proposed to explain the experimental results. In addition, this charge-orbital model is highly inconsistent with the electronic balance. On the contrary, these reflections can be easily understood as arising from the anisotropy of charge distribution induced by the presence of local distortions, i.e., due to a structural phase transition.