Comment on ``Comparison of the Cc and R3c space groups for the superlattice phase of Pb(Zr₀.₅₂Ti₀.₄₈)O₃''

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The two-phase (space groups Cc and Cm) structural model recently proposed for the modeling of the neutron powder diffaction pattern collected on Pb(ZrₓTi₁₋ₓ)O₃ (PZT) sample with x≈ 0.52 [R. Ranjan, A. K. Singh, Ragini, and D. Pandey. Phys. Rev. B 71, 092101 (2005)] is shown to neglect the hkl dependent (anisotropic) line broadening. The most serious problem with this model is that it assigns octahedral tilts to a wrong phase. Instead of correctly taking the anisotropic line broadening into account, this model used low symmetry phases to minimize the residuals during Rietveld refinement. The essential features of a model taking the hkl dependent line broadening into account are summarized. It has already been reported that once the anisotropic line broadening, revealed by high resolution neutron powder diffraction instrument, is correctly taken into account the model with R3c and Cm space group symmetries describes all Bragg peaks and their intensities well [J. Frantti, S. Eriksson, S. Hull, V. Lantto, H. Rundlöf, and M. Kakihana. J. Phys.: Condens. Matter 15, 6031 (2003).]. It was further shown that the Cm+R3c model is consistent with the structural features observed at other compositions and temperatures, which is particularly important in the vicinity of the phase boundary. Also problems related to sample preparation and data collection are pointed out.