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 Pb ₅Bi₆Se₁₄ [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.