Site occupancy and cation binding states in reduced polycrystalline SrxBa1−xNb2O6

Site occupancy and cation binding states in the proposed thermoelectric n-type oxide SrxBa1−xNb2O6 (SBN100x) were investigated using X-ray photoelectron spectroscopy (XPS). Sr 3d XPS spectra from unreduced polycrystalline SBN100x with various compositions contained two distinct spin-orbit doublets corresponding to Sr occupying either A1 or A2 positions in the SBN lattice; the higher binding energy state was associated with Sr ions at A2 sites, presumably due to their increased coordination over Sr at A1 sites. To gain insight into optimizing the thermoelectric properties of reduced SBN, sintered SBN50 specimens were reduced in Ar/H2 or N2/H2 ambient. A decrease in the average Nb valence was observed in Nb 3d photoemission through the growth of low-binding energy components after reduction in either environment; evidence of surface NbN formation was apparent with longer reducing times in N2/H2. Both the single-component Ba 3d emission and the A2 component of the Sr 3d spectra show shifting to lower binding...