Dielectric properties and defect chemistry of (Ba1−xLax)(Ti1−xLux)O3 ceramics

Abstract

The single-phase (Ba1−xLax)(Ti1−xLux)O3 (0.02 ≤ x ≤ 0.05) ceramics (BLTL) were prepared at 1400 °C using a solid-state reaction method. The structure, microstructure, point defects, and dielectric properties of BLTL were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, electron paramagnetic resonance (EPR), and dielectric measurements. The fine-grained BLTL (∼0.9 μm) is tetragonal for x ≤ 0.03 and cubic for x ≥ 0.04. The x = 0.05 ceramic with Y5S dielectric specification (ε′RT ∼1800) exhibits a lowest dielectric loss (tan δ = 0.01) as compared to (Ba1−xLax)(Ti1−xRx)O3 with x = 0.05 (R = Tb, Dy). A regularity is discovered that the dielectric loss decreases with lanthanide contraction when BaTiO3 is co-doped with La and R (R is a rare-earth ion) under the same preparation conditions. Lu3+ exhibits a weak amphoteric behavior in BLTL. The defect chemistry, the low dielectric loss, the origin of EPR signals of vacancy point defects and an unexpected, broad and intense EPR signal at g = 2.2, are discussed. An approach to the completely self-compensated LaBa•−LuTi' mode with the increase of x is the main reason of the low dielectric loss.