Electrical and structural characteristics of lanthanum-doped barium titanate ceramics

TLDR

Single phase La‑doped BaTiO₃ with formula Ba₁₋ₓLaₓTi₁₋ₓ/₄O₃ (0 ≤ x ≤ 0.20) was prepared by solid‑state reaction of oxide mixtures at 1350 °C for 3 days in O₂. Increasing La content reduces the tetragonal distortion, drives the material cubic for x ≥ 0.05, lowers the tetragonal/cubic and orthorhombic/tetragonal transition temperatures that merge near x ≈ 0.08, raises the permittivity maximum from ~10 000 at x = 0 to ~25 000 at x = 0.06 before broadening into relaxor‑type behavior at higher x, and causes a transition from insulating to semiconducting behavior when fired in air due to oxygen loss.

Abstract

Single phase La-doped BaTiO3 with the formula Ba1−xLaxTi1−x/4O3: 0⩽x⩽0.20 was prepared by solid state reaction of oxide mixtures at 1350 °C, 3 days, in O2. The tetragonal distortion in undoped BaTiO3 decreased with x and samples were cubic for x⩾0.05. Both the tetragonal/cubic and orthorhombic/tetragonal transition temperatures decreased with x, but at different rates, and appeared to coalesce at x∼0.08. The value of the permittivity maximum at the tetragonal/cubic phase transition in ceramic samples increased from ∼10 000 for x=0 at 130 °C to ∼25 000 for x=0.06 at ∼−9 °C. At larger x, the permittivity maximum broadened, showed “relaxor”-type frequency dependent permittivity characteristics and continued to move to lower temperatures. Samples fired in O2 were insulating and showed no signs of donor doping whereas air-fired samples were semiconducting, attributable to oxygen loss.