STRUCTURE DETERMINATION OF PbZrO₃ USING X-RAY ANOMALOUS DISPERSION. K. Yamasaki, Y. Soejima, Department of Physics, Kyushu University, Fukuoka 812-81, Japan, K. F. Fischer, Fachrichtung Kristallographie, der Universität des Saarlandes, D-66041 Saarbrücken, Germany (FRG)

On the basis of the method for superlattice structure analysis using X-ray anomalous dispersion, the intensity of several superlattice reflections from a PbZrO₃ single crystal have been re-examined: the intensity measurements were made as a function of incident X-ray energy around the Pb L_III and Zr K absorption edges. Since the structure factors of superlattice reflection are directly concerned with the displacement of anomalous scatterers from the higher symmetry position, they are expected to vary around the absorption edge when the anomalous scatteres have displacement. On the other hand, the structure factor is invariant when anomalous scatterers have no displacement. The experimental results show: Pb atoms have displacements only on the ab plane in the orthorhombic unit cell, and the pattern of the displacement is in anti-phase along the c direction. Zr atoms have an anti-phase type of displacements both on the ab plane and along c. These results support the structure determination by Glazer, Roleder and Dec (1993), except for the Zr displacement along c.

For refining our model, data were collected using 0.35 Å radiation up to sin[[theta]]/[[lambda]]=1.0 Å^-l. To avoid a serious problem of domains, and to obtain information on the atomic displacement as precisely as possible, only superlattice reflections were used. The structure has been determined with R-factor 5 %: the results show anti-phase displacements of Zr atoms along c; this is consistent with the results of the structure factor examination mentioned above. The present investigation requires that the anti-phase type of displacement of Zr atoms must be considered.