Spectroscopic characterization of a new series of bismuth tantalate pyrochlores doped with 3d-ions

Abstract

X-ray spectroscopy methods (XPS, NEXAFS) were used to study the electronic state of the ions that make up pyrochlores (sp. gr. Fd-3m, No. 227) Bi2Mg1-xMxTa2O9+Δ (M − Cr,Mn,Fe,Co,Ni,Cu). It has been established that doping of bismuth magnesium tantalate pyrochlore with 3d-ions does not affect the electronic state of bismuth and magnesium ions, which are found in the ionic form Bi(+3), Mg(+2). Tantalum ions are in the same charge state Ta(+5-δ) due to the characteristic shift of the energy position of peaks towards the lower energies compared to the binding energy in pentavalent tantalum oxide. An energy shift in the Ta4f and Ta5p spectra is observed for all transition ions without a strict regularity in the magnitude of the signal shift depending on the nature of the dopant. Ions of some 3d-elements in the composition of pyrochlores, according to X-ray spectroscopy, have several oxidation states, for example, Cu(+1,+2), Co(+2,+3), Mn(+2,+3), Cr(+3,+6). The iron and nickel ions predominantly have the +3 and + 2 oxidation states, respectively.