Antiferrodistortive phase transition in Pb(Ti_0.48Zr_0.52)O₃ :Space group of the lowest temperature monoclinic phase

Abstract

Ranjan et al. [Phys. Rev. B 65, 060102(R) (2002)] have recently presented results of a powder neutron-diffraction study of the high-temperature monoclinic ( F^HT_M ) to low-temperature monoclinic (F^LT_M) phase transition in Pb (Ti_1−xZr_x)O₃ discovered by Ragini et al. [Phys. Rev. B 64, 054101 (2001)]. They attribute the presence of superlattice reflections in the diffraction data to tilting of oxygen octahedra and propose a monoclinic space group Pc for the F^LT_M phase. It is shown that for the model proposed by Ranjan et al., the correct space group of the F^LT_M phase should be Cc . This has also been corroborated by a group-theoretical approach to the problem. A different set of refined structural parameters for the Cc space group obtained from the Rietveld analysis of the powder neutron-diffraction data of Ranjan et al. is also presented.