Antiferrodistortive phase transition in Pb(Ti_0.48Zr_0.52)O₃: a powder neutron diffraction study

Abstract

Results of a powder neutron diffraction study of the high-temperature monoclinic (F_M^HT) to a low-temperature monoclinic (F_M^LT) phase transition in Pb(Ti_1-xZr_x)O₃ discovered recently by Ragini et al. are presented for x=0.520. The powder neutron diffraction pattern of the F_M^LT phase contains superlattice reflections which have all odd hkl (h≠k≠l) Miller indices with respect to a doubled elementary perovskite cell, characteristic of antiphase tilting of oxygen octahedra. In analogy to other perovskite systems, the appearance of these superlattice reflections is attributed to an instability at the R point of the cubic Brillouin zone. We show that the most plausible space group of the F_M^LT phase is Pc. Results of Rietveld refinement for this space group are presented to show that the oxygen octahedra indeed undergo antiphase rotations about [001] direction.