A reinvestigation of Sillen X_1-type lead tellurium oxyhalides, Pb_3TeO_4X_2 (X = Cl, Br, I)

摘要

The oxyhalides Pb_3TeO_4X_2 (X = Cl, Br, I) have been prepared from Pb_3O_2X_2 and TeO_2. All three compounds are isostructural and adopt the Nd_2O_2Te (PbBiO_2I) structure type (I 4/m, Z = 1) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite. Pb_5IO_4(OH)_2Cl_3 but not Pb/Sb in nadorite PbSbO_2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillen-type) multinary oxyhalides of lead.