Determining metal ion distributions using resonant scattering at very high-energy K-edges: Bi/Pb in Pb₅Bi₆Se₁₄

Powder diffraction data collected at ∼86 keV, and just below both the Pb and the Bi K-edges, on an imaging plate detector using synchrotron radiation from the Advanced Photon Source have been used to examine the Pb/Bi distribution over the 11 crystallographically distinct sites in Pb₅Bi₆Se₁₄ [space group P2₁/m, a = 16.0096 (2) Å, b = 4.20148 (4) Å, c = 21.5689 (3) Å and β = 97.537 (1)°]. The scattering factors needed for the analyses were determined both by Kramers–Kronig transformation of absorption spectra and by analyses of diffraction patterns from reference compounds. Even with the relatively low scattering contrast that is available at the K-edges, it was possible to determine the Pb/Bi distribution and probe the presence of cation site vacancies in the material. The current results indicate that resonant scattering measurements at high-energy K-edges are a viable, and perhaps preferable, route to site occupancies when absorption from the sample or sample environment/container is a major barrier to the acquisition of high-quality resonant scattering data at lower-energy edges.