Antiferrodistortive phase transition in Pb(Ti<SUB>0.48</SUB>Zr<SUB>0.52</SUB>)O<SUB>3</SUB>: a powder neutron diffraction study

Results of a powder neutron diffraction study of the high-temperature monoclinic (FMHT) to a low-temperature monoclinic (FMLT) phase transition in Pb(Ti1-xZrx)O3 discovered recently by Ragini et al. are presented for x=0.520. The powder neutron diffraction pattern of the FMLT phase contains superlattice reflections which have all odd hkl (h&#8800;k&#8800;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 FMLT 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