A powder X-ray diffraction study of lead chloride oxalate Pb2Cl2(C2O4):: ab initio structure determination and thermal behavior

Mixed lead chloride oxalate, Pb2Cl2(C2O4), has been obtained in a polycrystalline form in the course of a study on precursors of nanocrystalline PZT-type oxides. Its crystal structure has been solved ab initio from powder diffraction data collected using a monochromatic radiation from a conventional X-ray source. The symmetry is monoclinic, space group C2/m, the cell dimensions are a = 5.9411(3) Angstrom, b = 5.8714(4) Angstrom, c = 9.4212(4) Angstrom, beta = 95.232(4)degrees and Z = 2. The structure consists of a stacking of complex double sheets, built from lead polyhedra, parallel to (001) and connected together through oxalate groups. The lead atom is nine-fold coordinated by four 0 atoms from one bidentate and two monodentate oxalate groups and five Cl atoms. The polyhedron can be described as a highly distorted square antiprism mono-capped by a Cl atom. The thermal behavior of lead chloride oxalate, in vacuum and in air, is carefully described from temperature-dependent powder diffraction and thermogravimetric measurements. It is shown that reaction pathways are complicated by the identification of various oxide chloride phases. (C) 2003 International Centre for Diffraction Data.