Dielectric permittivity and Cr3+ impurity ion probe luminescence in SrTiO3 sol–gel ceramics

In order to inspect bulk properties of the SrTiO3 ceramics grains, dielectric permittivity and temperature shift of a zero-phonon R-emission line of the Cr3+ impurity-ion probes were studied in sol–gel SrTiO3:Cr (3 × 10−2%) ceramics of the average grain size ∼24 μm. We found that non-dispersive permittivity (100 Hz to 1 MHz) increases on cooling less steeply than in single crystals reaching ∼5000 at 30 K. At lower temperatures the dispersion appears and the permittivity saturates at ∼8 K (ɛ′ ≈ 7000, 400 Hz). However, the temperature shift of the R-line in ceramics remains practically identical to that for SrTiO3 single crystals, in which R-line shifts with temperature is Δν ∼ 1/ɛ′ ∼ ω TO 1 2 . This indicates that the bulk of the grains in ceramics exhibits properties inherent to SrTiO3 quantum paraelectric, which agrees with the “generalized brick-wall” approach developed recently to describe polarization response of granular high permittivity materials.