Synthesis and dielectric-magnetic properties of rare-earth (La, Nd, Sm)-modified Bi₄Ti₃O₁₂

Rare-earth (RE = La, Nd, Sm)-substitution into BiT (Bi_4-XRE _XTi₃O₁₂) was conducted in a composition range of 0 ≤ X ≤ 3.0. BiT powders, into which fixed amounts of RE cations were incorporated, were directly synthesized by low-temperature calcination of coprecipitated precursors. Complete substitution with RE was achieved for samples up to X = 2.5 at 1100°C. Dielectric permittivity (ε_τ)-temperature curves of the La-2.0, Nd-2.0, and Sm-2.0 ceramics showed ε_τ maxima in a frequency-dependent manner. The ε_τ maxima were located at around 540-560°C (at 1 kHz), which corresponded to the transition from the ferroelectric to paraelectric phase. Increasing Nd-substitution from X = 2.0 to 2.5 resulted in a much suppressed ε_τ maximum at 200-300°C, which may be due to substantial reduction in the structural distortion giving rise to ferroelectricity of the BiT-based phase. The appearance and enhancement of magnetization was found for the Nd- and Sm-substituted BiT samples. They revealed specified magnetization-magnetic field curves with a small hysteresis loop, suggesting the presence of a weak canted antiterromagnetic interaction.