The high pressure behavior of galenobismutite, PbBi2S4 : A synchrotron single crystal X-ray diffraction study

High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a F-E-f(E) plot, yielding V-0 = 697.4(8) angstrom(3), K-0 = 51(1) GPa and K' = 5.0(2). The axial moduli were M-0a = 115(7) GPa and M-a' = 28(2) for the a axis, M-0b = 162(3) GPa and M-b' = 8(3) for the b axis, M-0c = 142(8) GPa and M-c' = 26(2) for the c axis, with refined values of a(0), b(0), c(0) equal to 11.791(7) angstrom, 14.540(6) angstrom 4.076(3) angstrom, respectively, and a ratio equal to M-0a:M-0b:M-0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.