Deutsche Neutronenstreutagung

Mixed valence lead oxide phases obtained at ambient pressure are reported by Byström [1] belonging to either black [2] or red minium [1, 3]. For red minium the composition of Pb₃O₄ is described without any variance in the number of oxygen atoms [1, 3]. The formula could therefore be written as Pb(II)₂Pb(IV)O₄, expressing the different oxidation states of lead. For the black minium Byström [1] proposed two structures, namely, α-PbO_x and β-PbO_x. Pure α-PbO_x exits for 1.628 (~ Pb₁₂O_19.5) > x ≥ 1.475 (~ Pb₁₂O_17.7). For lower x, β-PbO_x and red minium coexist in the range of x = 1.475 – 1.352 (~ Pb₁₂O_16.2). We synthesized phase pure Pb₁₂O₁₉ by decomposing PbO_1.96(2) at 600 K for 1390 h, showing a dark brown color. Neutron time-of-flight (TOF) total scattering data (nPDF) were collected on the powder diffractometer POWGEN@SNS (Oak Ridge National Lab, USA) within the Proposal IPTS-20531 and respective synchrotron radiation data (xPDF) on the P02.1@Petra III (DESY, Germany) powder diffractometer at E = 59.78(3) keV (λ = 20.74(4) pm). The combined machine-learning (ML) – density function theory (DFT) – pair distribution function (PDF) approach [4] was used to refine the structure of Pb₁₂O₁₉ starting with an unbiased set of structural models using both neutron and X-ray PDF data sets at the same time. Based on the ML-DFT-xPDF-nPDF refinements a structure model with a 2x2x1 bigger unit cell compared to those reported by Byström [1] was found. Instead of the CaF₂-type [1] derived arachno-cube like coordination of the lead atoms, which could hardly be described as strongly distorted octahedra, different coordination numbers were found, giving rise for differently pronounced stereo-chemical activities of the Pb 6s² lone pairs and void channels in the structure which might be described with a triangular shape. The new crystal structure enables to additionally describe the non-explained weak reflections of the earlier findings [1].
1] A. Byström, Arkiv Kemi Mineral. Geol. 20(4) (1945) 1-31.
[2] M. Le Blanc, E. Eberius, Z. für Phys. Chem. 160A(1) (1932) 69-100.
[3] S.T. Gross, J. Am. Chem. Soc. 65(6) (1943) 1107-1110.
[4] M. Klove, S. Sommer, B.B. Iversen, B. Hammer, W. Dononelli, Adv Mater (2023) e2208220.

Figure: PDF-Plots of the refinement of the Pb₁₂O₁₉ structure to the synchrotron (a) and neutron data (b).