Study on a new tetragonal phase of Nb-doped lead titanate zirconate by synchrotron X-ray powder diffraction

A ferroelectric phase of Nb-doped Pb(ZrxTi1-x)O-3(x congruent to 0.97) was studied by synchrotron X-ray powder diffraction. It was found that this phase is of a tetragonal symmetry with unit-cell parameters a = 4.08401(2) Angstrom and c = 4.06738(2) Angstrom. Extra weak reflections also appear in the diffraction pattern, which may come from an unknown minor phase or superlattice structure of the tetragonal phase which should be related to a modulation along the c axis. With space group P4mm, crystal structural parameters were initially obtained by direct methods, and then were refined by the Rietveld method. Three structural models with different stoichiometries were examined. The results showed that some Zr/Ti atoms at the 1b site were replaced by Nb atoms. A chemical formula for this phase should be Pb-0.987(Zr0.945Ti0.029Nb0.026)O-3, and vacancies occur at the 1a site. The crystal structure and its relationship with ferroelectricity were described in detail. (C) 1999 Elsevier Science Ltd. All rights reserved.