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Rare-earth (RE ¼ La, Nd, Sm)-substitution into BiT (Bi 4ÀX RE X Ti 3 O 12 ) 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 lowtemperature calcination of coprecipitated precursors. Complete substitution with RE was achieved for samples up to X ¼ 2:5 at 1100 C. Dielectric permittivity (" r )-temperature curves of the La-2.0, Nd-2.0, and Sm-2.0 ceramics showed " r maxima in a frequency-dependent manner. The " r 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 ¼ 2:0 to 2.5 resulted in a much suppressed " r 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 Smsubstituted BiT samples. They revealed specified magnetization-magnetic field curves with a small hysteresis loop, suggesting the presence of a weak canted antiferromagnetic interaction.

A BaBi 2 Nb 2 O 9 (BBN) powder was synthesized by the double-calcination method at 800 C, which considerably suppressed the formation of the stable intermediate Ba 5 Nb 4 O 15 phase. Sintering of the stoichiometric BBN powder at 950 C for 4 h resulted in the production of densified BBN ceramics with a relative density of 90%. The La 3þ substitution was conducted for Ba-deficient BBN powders with nominal compositions of x ¼ 0:03 and 0.10 in Ba 1Àx Bi 2 Nb 2 O 9À , which were pre-formed by the double-calcination method prior to sintering. The result of the phase identification with XRD, microstructural observation and elemental analysis with SEM and TEM, and dielectric permittivity-temperature relationship that were obtained for the La 3þ -doped BBN ceramics suggested that the La 3þ cations could be predominantly substituted for the Ba 2þ -sites in the tetragonal BBN structure.

Reaction controlled sintering was applied to the fabrication of BaBi 2 Nb 2 O 9 (BBN) ceramics at lower temperature. A powder mixture of BaCO 3 and Nb 2 O 5 was heated at 600°C in a 1st step calcination to produce a binary precursor of BaNb 2 O 6 . The pre-heated powder was then mixed with a fixed amount of Bi 2 O 3 , which was subsequently pressed into a disk pellet. After a powder compact of the mixture was subjected to heating at 950°C for 4 h, a BBN bulk sample with a relative density of 92% was successfully obtained. The low-temperature fabrication of dense BBN ceramics could be attributed to the inhibited formation of an intermediate phase of Ba 5 Nb 4 O 15 and the production of submicron powder with an appropriate reactivity during a 1st step calcination.

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