Low-temperature formation of Pb2OF2 with O/F anion ordering by solid state reaction

Highlights: • Pb₂OF₂ was formed by a solid state reaction between PbO and PbF₂ at 200 °C. • The combination of XRD and ¹⁹F MAS NMR confirmed the O/F ordering. • Due to the O/F ordering, the one-dimensional chains of OPb₄ is isolated. • The isolated one-dimensional chains of OPb₄ makes the band gap greater than PbO. -- Abstract: The lead oxyfluoride Pb₂OF₂ was formed by heating a mixture of equimolar PbO and PbF₂ at a relatively low temperature of 200 °C in air, suggesting that high ionic diffusion occurs in this reaction at low temperature. The crystal structure of Pb₂OF₂ was refined by Rietveld analysis using synchrotron X-ray diffraction (SXRD) data and the local structure around fluorine was evaluated by solid state ¹⁹F magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The combination of SXRD and NMR confirmed that oxygen and fluorine ions in Pb₂OF₂ are in an ordered arrangement. The band gap of Pb₂OF₂ estimated from the absorption edge (λ = 325 nm) was 3.8 eV. Due to the O/F ordering, the one-dimensional chains of OPb₄ tetrahedra along the c-axis of the tetragonal cell were isolated from each other by one-dimensional chains of FPb₄ tetrahedra, which makes the band gap greater than that of PbO.