Dielectric permittivity in weakly concentrated SrTiO₃:Mn crystals and ceramics

Dielectric permittivity ε + iε'' (100 Hz – 1 MHz) supplemented by IR (20 – 650 cm⁻¹) reflectivity and Micro-Raman spectra studies were performed on weakly concentrated SrTiO₃:Mn (0.1%) crystals and ceramics sintered with deficit of Ti, keeping the ratio (Ti+Mn)/Sr = 1. Surprisingly, magnitude of permittivity in SrTiO₃:Mn crystals appeared to be depressed at low temperatures as in ceramics, reaching only ∼3000 at T = 10 K. At the same time, low temperature IR reflectivity in STO:Mn crystals evidences that TO phonons contribution into low-frequency permittivity is nearly the same as in undoped serial SrTiO₃ quantum paraelectric crystals. Together with Micro-Raman data, such features are understood as evidences of STO:Mn(0.1%) crystals inhomogeneity and presence of Mn oxides enriched nano-regions. Currently discussed in literature Mn doping related low-temperature dielectric relaxation is faintly pronounced in dielectric losses of STO:Mn(0.1%) crystals and ceramics and increased in reduced crystals, where at least two relaxation contributions with activation energy ∼40 meV and ∼120 meV can be distinguished displaying at ∼20 – 40 K and 76-114 K temperature regions respectively. The fist relaxation is attributed to reorientation of polaronic defects localized on Mn²⁺ related centres. Possible nature of the second one is discussed.