Electron paramagnetic resonance of Mn⁴⁺ in BaTiO₃

The Electron Paramagnetic Resonance (EPR) of Mn4+ in the rhombohedral low- temperature phase of BaTiO3 has been observed at 19.3 and 13.0 GHz. The spectra have axial symmetry along 〈111〉 directions. Intensity measurements prove that the Mn4+ EPR reflects {111} domain orientation. The spin-Hamiltonian constants are g{norm of matrix}=1.9968(19), g{norm of matrix}=2.0015(5), A{norm of matrix}=67.48(5)×10-4cm-1, A{norm of matrix}=73.04(15)×10-4cm-1, and D=0.65(1)cm-1 at 4.2 K. The very large D value is more than 20 times that found for the isoelectronic Cr3+. The latter ion remains centered in its surrounding octahedral oxygen cage, whereas the Mn4+ is off-center with similar coordinates as Ti4+. This result is deduced from a superposition-model analysis. © 1987.