Acta Crystallographica Section B

Structural Science

Volume 53, Part 1 (February 1997)

research papers

Acta Cryst. (1997). B53, 135-142 [ doi:10.1107/S0108768196012414 ]

A Re-investigation of the Crystal Structure of the Perovskite PbZrO₃ by X-ray and Neutron Diffraction

D. L. Corker, A. M. Glazer, J. Dec, K. Roleder and R. W. Whatmore

Abstract: The crystal structure of the perovskite lead zirconate PbZrO₃ has been redetermined using single-crystal X-ray diffraction (Mo K [alpha] radiation, [lambda] = 0.71069 Å). Single-crystal data at 100 K: space group. Pbam, a = 5.884 (1), b = 11.787 (3), c = 8.231 (2) Å, V = 570.85 Å³ with Z = 8, [mu] = 612.6 cm^-1, D_x = 8.06 Mg m^-3, F(000) = 1168, final R = 0.033, wR = 0.061 over 555 reflections with I > 2 [sigma] (I). An investigation is made into previous contradicting reports of a possible disorder in the O atoms and their origin by examining the crystal pseudo-symmetry. Information distinguishing an ordered and disordered oxygen substructure is shown to reside in weak l odd reflections. Because of their extremely low intensities these reflections have not contributed sufficiently in previous X-ray structure investigations and hence, to date, conclusive evidence differentiating between ordered and disordered models has not been possible. By collecting single-crystal X-ray data at low temperature and by using exceptionally long scans on selected hkl, l odd, reflections, a new accurate structure determination is presented and discussed, showing the true ordered oxygen positions. Because of the large difference in scattering factors between lead and oxygen when using X-rays, a neutron diffraction Rietveld refinement using polycrystalline samples (D1A instrument, ILL, [lambda] = 1.90788 Å) is also reported as further evidence to support the true ordered oxygen structure revealed by the low-temperature X-ray analysis.