EPR and NEXAFS spectroscopy of BiNb1-xFexO4-δ ceramics

The methods of EPR and NEXAFS spectroscopy were employed for the study of BiNb1-xFexO4-δ solid solutions of triclinic and orthorhombic modifications. The analysis of the NEXAFS Fe2p-spectra of iron oxides and the iron-containing solid solutions revealed that Fe atoms were mainly in an oxidation state of +3. In the EPR spectra of the BiNb1-xFexO4-δ samples of orthorhombic modification, a broad line with the center at g of 2.16-2.37 was registered along with the low-intensity signal with a g-factor of ∼4.3 observed on its low-field wing. EPR spectra of the triclinic structure samples exhibited a complex system of lines in the range of 80-300 mT. An intense complex line having features at g of 4.74-4.80, 4.04-4.10 and 3.76-3.80 was recognized in the low-field signal. The low-field wing of the line was complicated by a shoulder with g of 5.3 and by a line in the form of an absorption signal with g of 7.7-8.0. As a result of the modeling of EPR spectra, the spin-Hamiltonian parameters of Fe(III) in the structure of BiNb1-xFexO4-δ of triclinic modification were obtained.