Electron spin resonance investigation of Mn²⁺ ions and their dynamics in Mn-doped SrTiO₃

Abstract

Using electron spin resonance (ESR), the lattice position and dynamic properties of Mn²⁺ ions were studied in 0.5 and 2 at. % manganese-doped SrTiO₃ ceramics prepared by the conventional mixed oxide method. The measurements show that Mn²⁺ ions preferably (up to 97%) substitute for the Sr if the ceramics are prepared with a deficit of Sr ions. Motional narrowing of the Mn²⁺ ESR spectrum was observed when the temperature increased from 120  to 240–250 K, which was explained as a manifestation of the off-center position of this ion at the Sr site. From the analysis of the ESR spectra, the activation energy E_a=86 mV and frequency factor 1/τ₀≈(1–5)10¹³ s^-1 for the jumping of the impurity between symmetrical off-center positions were determined. Both are in agreement with those previously derived from the dielectric relaxation. This proves that the origin of the dielectric anomaly in SrTiO₃:Mn is produced by the reorientation dynamics of Mn²⁺ dipoles.