Dielectric permittivity epsilon' + i epsilon '' (100 Hz - 1 MHz) supplemented by IR (20 - 650 cm(-1)) reflectivity and Micro-Raman spectra studies were performed on weakly concentrated SrTiO(3):Mn (0.1%) crystals and ceramics sintered with deficit of Ti, keeping the ratio (Ti+Mn)/Sr = 1. Surprisingly, magnitude of permittivity in SrTiO(3):Mn crystals appeared to be depressed at low temperatures as in ceramics, reaching only similar to 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 SrTiO(3) 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 similar to 40 meV and similar to 120 meV can be distinguished displaying at similar to 20-40 K and 76-114 K temperature regions respectively. The fist relaxation is attributed to reorientation of polaronic defects localized on Mn(2+) related centres. Possible nature of the second one is discussed.
Dielectric permittivity in weakly concentrated SrTiO(3):Mn crystals and ceramics
AZZONI, CARLO;GALINETTO, PIETRO;MOZZATI, MARIA CRISTINA;
2007-01-01
Abstract
Dielectric permittivity epsilon' + i epsilon '' (100 Hz - 1 MHz) supplemented by IR (20 - 650 cm(-1)) reflectivity and Micro-Raman spectra studies were performed on weakly concentrated SrTiO(3):Mn (0.1%) crystals and ceramics sintered with deficit of Ti, keeping the ratio (Ti+Mn)/Sr = 1. Surprisingly, magnitude of permittivity in SrTiO(3):Mn crystals appeared to be depressed at low temperatures as in ceramics, reaching only similar to 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 SrTiO(3) 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 similar to 40 meV and similar to 120 meV can be distinguished displaying at similar to 20-40 K and 76-114 K temperature regions respectively. The fist relaxation is attributed to reorientation of polaronic defects localized on Mn(2+) related centres. Possible nature of the second one is discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
