On BSCCO Superconductor-Related Bi2Sr2MnO6+x and BiPbSr2MnO6: X-Ray Absorption Spectroscopy and Diffraction Study

Bi2Sr2MnO6+x and BiPbSr2MnO6, isotypic with the 2201 BSCCO superconductor, were investigated by X-ray powder diffraction and X-ray absorption spectroscopy (synchrotron radiation). The unit-cell constants are a = 21.796(3), b = 5.4268(7), c = 23.612(2) Å, and a = 5.3186(8), b = 5.3892(8), c = 23.765(3) Å, respectively. Superlattice modulation peaks (h ≠ 4n) are evident in the diffractogram of the first phase. XAFS spectra at the K edge of manganese were recorded for the two compounds and for metallic Mn, MnO, and Mn2O3. An energy shift of about 1.5 eV is observed between the profiles of the two phases. By comparison of spectral features with those of the simple oxides, the oxidation state of Mn is inferred to be +2.6(1) and +2.9(1) in Bi2Sr2MnO6+x and BiPbSr2MnO6, respectively.