Dielectric properties of Mn doped SrTiO₃

Abstract

The dielectric permittivity (100 Hz–1 MHz) and IR reflectivity of SrTiO3:Mn(0.1 at.%) crystals and SrTiO3:Mn(0.1–3 at.%) ceramics prepared maintaining the ratio (Sr+Mn)/ Ti = 1 or (Ti+Mn)/Sr = 1 (A- and B-type ceramics, respectively) were studied. Surprisingly, the magnitude and ε'(T) dependence for the crystals and B-type ceramics with 0.1 at.% of Mn appeared to be nearly the same; the magnitudes rise on cooling and reach ∼3000 at T = 7 K. At the same time, IR spectra of SrTiO3:Mn(0.1 at.%) crystals reveal that TO (transverse optical) phonons yield a magnitude of low frequency permittivity of ∼4000 at T = 5 K, evidencing crystal inhomogeneity. Both crystals, like B-type SrTiO3:Mn(0.1 at.%) ceramics, reveal faint low temperature relaxations with the Arrhenius activation energies ∼37–40 meV and ∼120–130 meV (P- and T-relaxations). These relaxations emerge in losses only and were tentatively attributed to reorientation of defects associated with MnTi2+–O−-type polaronic centres and Oh1–D4h18 phase transition related effects, respectively. In reduced crystals P-relaxation strongly enhances, becoming distinctly seen in the real part of the permittivity. More heavily Mn doped A- and B-type ceramics reveal strongly pronounced Arrhenius-type dielectric relaxation with activation energy ∼59–68 meV depending on the Mn concentration.