Impurity centers and host microstructure in weakly doped SrTiO 3:Mn crystals: New findings

Abstract

Electron paramagnetic resonance (EPR), optical absorption and low-frequency (100 Hz - 1 MHz) dielectric permittivity investigations on Verneuil as-grown and reduced SrTiO3:Mn (0.1% at.) crystals were carried out to establish connection between the structure of Mn doping related centers and the SrTiO3 dielectric properties. At room temperature the EPR spectrum of as-grown crystals evidences isotropic Mn4+ and Mn2+ centers. The Mn2+/Mn4+ ratio increases, according to the EPR spectra, by decreasing the temperature and the signals intensity of both centers strongly decreases approaching T∼120 K. Such behavior is attributed to antiferromagnetic interaction in MnO and MnO2 nano-clusters. Also the dielectric permittivity behavior evidences samples inhomogeneity as well as absence of pronounced dielectric relaxation in as grown crystals. In reduced crystals the Mn2+ concentration increases and the dielectric relaxation emerges evidencing a polaronic-related nature of dipole reorientations. © 2007 IOP Publishing Ltd.