Structural, electrical and optical properties of Ba(Ti1−xYb4x/3)O3 ceramics

Ytterbium (Yb) doped barium titanates, Ba(Ti1−xYb4x/3)O3 (0.00≤x≤0.10, in a step of 0.02) have been prepared through the solid state reaction route. Structural studies suggested a transition from tetragonal to cubic symmetry with increase in Yb3+ ion content, supported by Rietveld refinement technique. Photoluminescence study confirmed formation of shallow defects. The prepared materials are found to belong to violet, blue and green zone. Optical band gap values calculated from UV–visual diffuse reflectance spectra showed a decreasing trend with increase in Yb3+ ion concentration. Disk shaped pellets were prepared using PVA as binder. The effect of the partial presence of Yb3+ ions at Ti4+ ionic sites on the microstructure, dielectric and relaxor behavior of the ceramics were investigated. A drastic decrease in grain size is observed in the composition exhibiting the phase transition. Dielectric studies were performed over a wide temperature range from 15 K to 600 K at different frequencies. Normal ferroelectric character was obtained uptill x≤0.04 with subsequent increase in dielectric constant and a gradual decrease in the Curie temperature. Diffuse phase transition (DPT) was obtained at x=0.06 while relaxor like behavior was observed for x≥0.08. A sharp decrease in Curie temperature as well as dielectric constant followed. The dielectric relaxation for x=0.08 and 0.10 was modeled using the Vogel–Fulcher relation and a decrease in activation energy and an increase in frequency dispersion with increasing Yb3+ ion content was observed. P–E hysteresis loops showed a domain pinning effect which increased with increase in Yb3+ ion content resulting in a decrease in the values of remnant polarization.