Structural resolution of the incommensurate phase ofα-PbO from x-ray- and neutron-powder-diffraction data

Abstract

The modulated structure of the incommensurate phase of α-PbO was determined from x-ray and neutron-powder-diffraction data. The four-dimensional structural refinement has led to the superspace group P(C2mb):(1¯ 1¯1). It has shown that even if the average atomic positions remain almost equivalent to those of the centrosymmetric tetragonal structure of PbO, the atomic modulated displacements only agree with a noncentrosymmetric space group. It has allowed us to give a first interpretation of the incommensurate behavior, which seems to point out a competition between α and β phases.