Electron spin resonance investigation of Mn^{2+} ions and their dynamics in manganese doped SrTiO_3

TL;DR

This study used electron spin resonance to analyze the lattice position and dynamics of Mn2+ ions in manganese-doped SrTiO3 ceramics, revealing off-center positions and reorientation dynamics linked to dielectric anomalies.

Contribution

It provides detailed ESR analysis of Mn2+ ions in SrTiO3, identifying off-center positions and quantifying their reorientation dynamics, which relate to dielectric properties.

Findings

Mn2+ ions substitute mainly for Sr at off-center positions.

Motional narrowing observed between 120 K and 250 K.

Activation energy for ion reorientation is 86 mV.

Abstract

Using electron spin resonance, lattice position and dynamic properties of Mn2+ ions were studied in 0.5 and 2 % manganese doped SrTiO3 ceramics prepared by conventional mixed oxide method. The measurements showed that Mn2+ ions substitute preferably up to 97 % for Sr if the ceramics is prepared with a deficit of Sr ions. Motional narrowing of the Mn2+ ESR spectrum was observed when temperature increases from 120 K to 240-250 K that was explained as a manifestation of off-center position of this ion at the Sr site. From the analysis of the ESR spectra the activation energy Ea = 86 mV and frequency factor 1/?0 ? (2-10)x10^(-14) 1/s for jumping of the impurity between symmetrical off-center positions were determined. Both values are in agreement with those derived previously from dielectric relaxation. This proves the origin of dielectric anomalies in SrTiO3:Mn as those produced by the reorientation dynamics of Mn2+ dipoles.