Broad-band dielectric spectroscopy analysis of relaxational dynamics in Mn-doped SrTiO3 ceramics

Dielectric properties of Sr1-x Mnx TiO3 ceramics (x=0-0.15 and 1) prepared by conventional mixed oxide method were investigated in radio frequency, high frequency, terahertz, and infrared ranges. It is shown that the real and imaginary parts of the dielectric permittivity between 100 Hz and 1 MHz exhibit a relaxation in the temperature range of 30-80 K, shifting to higher temperatures with increasing Mn content. The dielectric relaxation is also observed at higher frequencies (around 100 K for high frequencies and up to room temperature for terahertz frequencies) in Sr0.95 Mn0.05 TiO3 ceramics. Activation energy U∼ 52-78 meV and relaxation time pre-exponent τ0 ∼(1-12)× 10-14 s are obtained using Arrhenius and Vogel-Fulcher relations. Such dielectric behavior is attributed to Mn off-center relaxation at Sr site of highly polarizable SrTiO3 lattice. Moreover, a reduction of the phonon contribution to the dielectric constant with Mn doping accompanying a stiffening of the soft lattice mode is found in infrared reflectivity spectra and could be related to the interaction of the soft mode with off-centered Mn ions and polar clusters.