EPR evidence of extrinsic symmetry-breaking defects in nominally pureKTaO3

Abstract

EPR measurements on nominally pure (undoped) ${\mathrm{KTaO}}_3$ single crystals at low temperature (4.2 K) are reported. Evidence is brought of impurity defects analyzed through the experimental spin-Hamiltonian parameters. Axial EPR spectra of ${\mathrm{Fe}}^{3+}$ in different cation positions are detected. An orthorhombic spectrum is found and attributed to ${\mathrm{Fe}}^{3+}$ substituting for ${\mathrm{K}}^{+}$ ions and involving nearby potassium vacancies as charge compensators. Manganese impurities are also observed following illumination of the sample to cause a change of the Mn valence state.