Solid State Ionics, Vol.315, 33-39, 2018
Structural and transport properties of doped bismuth titanates and niobates
Cobalt- or Zn-doped bismuth titanates and Mg + Cu-doped bismuth niobate were synthesized by the method of organic-inorganic precursors combustion. Distribution of dopants over the sites of the pyrochlore structure was elucidated by X-ray powder diffraction structure refinement and pycnometric density analysis. Zinc and cobalt cations are mainly located in Bi sites appearing also in Ti sites at their high content. Mg cations are located only in Nb sites, while Cu cations are equally distributed between Bi and Nb sites. Magnetic susceptibility data confirm Co2+ state of cobalt atoms revealed by NEXAFS. Antiferromagnetic exchange appears when Co atoms enter the titanium sites. Electronic conductivity of p-type dominates for Co-doped samples in the 160-750 degrees C temperature range. The oxygen mobility and surface reactivity were studied by the oxygen isotope hetero-exchange with (CO2)-O-18 in isothermal and temperature-programmed modes. Mobility of the lattice oxygen can be described by a homogeneous model. The oxygen mobility and surface reactivity are comparable for doped bismuth titanates and niobates correlating with conductivity and being the highest for Co and Cu-doped samples with disordered distribution of dopants between lattice sites.