Features of the Preparation of Ni-Doped Bismuth Tantalate Pyrochlore

The possibility of high-temperature solid-phase synthesis of Ni-doped bismuth tantalate pyrochlore, not only from the oxide compounds BiTaO4 and NiO but also using nickel chloride NiCl2 as a precursor, was shown for the first time. The concentration range of the formation of nickel pyrochlore Bi2NixTa2O9-delta (0.85 <= x <= 1.0) at an equal molar ratio of bismuth(III)/tantalum(V) ions was determined. This indicates that the pyrochlore structure may be stable at 20-33% vacant bismuth sublattice. The influence of non-stoichiometric composition relative to bismuth and tantalum, by the example of Bi2 +/- xNiTa2O9-delta and Bi2NiTa2-xO9-delta (x <= 0.5) compositions, on the phase composition of ceramics was studied. X-ray powder diffraction phase analysis of Bi2Ni1+yTa1.75-yO9-delta samples made it possible to determine the solubility limit of nickel ions in the tantalum sublattice. It was shown that the molar ratio of metal atoms (Ta, Ni) in the B2O6 (B-Ni(II), Ta(V)) octahedral sublattice of mixed pyrochlores is also limited.