The Jahn–Teller effect in Cr5+-doped PbTiO3: a multi-frequency electron paramagnetic resonance study

Abstract

Electron paramagnetic resonance (EPR) spectra ofCr5+ defects incorporated onTi4+ sites in powderedceramics of PbTiO3 were investigated in the temperature range 50–400 K at 9 GHz (X), 34 GHz (Q) and 94 GHz(W band). The Jahn–Teller effect stabilizes the vibronic ground state of the3d1 electronof the Cr5+ ion and leads to a tetragonally distorted defect-O6 octahedron with thepoint symmetry D4h. The spontaneous electrical polarization present in the ferroelectric phase ofPbTiO3 appears as a further perturbation producing an additionalg-tensor contribution by the quadratic field effect. Its symmetry is dependent on the orientation of theelectrical polarization with respect to the Jahn–Teller distortion axis, the tetragonal axis of the defect-O6 octahedron. If the polarization of a domain is anti- or parallel to this axis, the local tetragonal symmetryof the Cr5+ ion persists whereas it is reduced by a perpendicular orientation.Anisotropic EPR spectra of tetragonally and orthorhombic distortedCr5+O612− are detected at low temperatures. Increasing the temperature, the peaks of the twospectra are broadened and a motionally averaged isotropic spectrum appears at200 K.