3C–6H phase transition in BaTiO3 induced by Fe ions: an electron paramagnetic resonance study

Abstract

X-ray diffraction (XRD) patterns and electron paramagnetic resonance (EPR) powder spectra (9 and34 GHz) of BaTiO3+0.04 BaO+0.5xFe2O3 (0.0005≤x≤0.02) ceramics were studied to investigate the development of the hexagonal phase(6H modification) of Fe-doped material in dependence upon doping levelx and sinteringtemperature Ts. Three axially symmetric EPR spectra assigned toFe3+ ions substituted at Ti lattice sites corresponding to the different distorted octahedra intetragonal and hexagonal modification are observed at room temperature. Thepresence of a hexagonal phase is shown by the XRD pattern and the EPR spectra.The 6H modification begins to occur at a nominal Fe concentration of betweenx = 0.005 and 0.01 and increases with increasing sintering temperature.BaTiO3 ceramicswith x = 0.02 sintered at Ts = 1400 °C is hexagonal. As discussed in the case of other 3d ions we propose the Jahn–Teller(JT) distortion as the driving force for the cubic–hexagonal transition at hightemperatures whereas a sufficiently high concentration of oxygen vacancies isthe second condition for this transformation process. In the case of Fe-dopedBaTiO3 a minimumconcentration of Fe4+ in the ceramic grains could trigger the transmutation into the hexagonal phase.