On the incorporation of iron into hexagonal barium titanate: I. electron paramagnetic resonance (EPR) study

Electron paramagnetic resonance (EPR) investigations of BaTiO₃  +  0.04 BaO  +  x/2 Fe₂O₃ (0.007  ⩽  x  ⩽  0.05) ceramics and BaTi_0.98Fe_0.02O₃ single crystals were performed to study the incorporation of Fe ions in the hexagonal 6H-BaTiO₃ lattice and their defect properties. The samples were characterized by x-ray diffraction and wavelength-dispersive x-ray electron probe microanalysis. EPR spectra were recorded both in X- and Q-bands at room temperature. Angle-dependent single crystal EPR investigations and simulations of the ceramic powder EPR spectra revealed three different centers, which can be attributed to Fe³⁺ ions incorporated on crystallographically different Ti sites. Only one of them was already known before. Two spectra with axial symmetry belong to isolated Fe³⁺ ions incorporated at Ti(1) sites (exclusively corner-sharing oxygen octahedra) and Ti(2) sites (face-sharing octahedra). The difference of their spectral parameters arises from the different trigonal distortions of the two types of octahedra. The third spectrum has orthorhombic symmetry and is caused by Fe³⁺ centers associated with a nearest-neighbor charge-compensating oxygen vacancy. A model for the location of this associate is proposed.