BLT Ceramics Research Articles

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Abstract Ceramics with formula (1 − x )Pb(Zr 0.52 Ti 0.48 )O 3 – x (Bi 3.25 La 0.75 )Ti 3 O 12 (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.

Microstructure Characteristics and Electrical Properties of Sintered (Bi,La)<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Ferroelectric Ceramics

1mm-thick BLT ceramics were sintered in accordance with a bulk ceramic fabrication process. All XRD peaks detected in the sintered ceramics were indexed as the Bi-layered perovskite structure without secondary phases. Density was increased with increasing the sintering temperature up to 1050°C and the maximum value was about 98% of the theoretical density. The remanent polarization (2Pr) value of BLT ceramic sintered at 1050°C was approximately 6.5 μC/cm2 at the applied voltage of 4.5kV. The calculated electromechanical couping factor (kt) of it was about 5% and the mechanical quality factor (Qm) was about 2200. From these results, a BLT ceramic target for plused laser deposition (PLD) system was successfully fabricated.

Ferroelectric phase transition of Nb-doped Bi3.25La0.75Ti3O12 ceramics

Bi3.25La0.75Ti3-yNbyO12 (y=0.0, 0.03, 0.09, 0.15, 0.21) were synthesized using the solid-state reaction method. The effects of Nb doping on ferroelectric properties were studied through dielectric and P-E measurements. The value of Pr increases with increasing Nb content. Bi3.25La0.75Ti3-yNbyO12 ceramics exhibit a maximum remanent polarization of Pr=27 μC/cm2 at an Nb content of y=0.09. These results indicate that Nb doping can improve the ferroelectric properties of BLT ceramics. The Curie temperature, Tc, decreased with increasing Nb-content, and the ferroelectric phase transition of BLTNy is a second-order transition without thermal hysteresis.

Phase Transition and Temperature Dependences of Electrical Properties of [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 Ceramics

Lead-free piezoelectric ceramics [Bi0.5(Na1-x-yKxLiy)0.5]TiO3 (abbreviated BNT–BKT–BLT) were prepared by the conventional oxide method. The effects of BKT and BLT amounts on the phase transition and electrical properties were examined. BNT–BKT–BLT ceramics give good performances with piezoelectric constant d33=216 pC/N and planar electromechanical coupling factor kp=40.1% at 20 mol % BKT with a fixed BLT amount of 10 mol %. Also, the optimal d33 of 173 pC/N and kp of 38.0% are obtained at 10 mol % and 7.5 mol % BLT, respectively when the BKT amount is 17.5 mol %. The addition of BKT reduces the depolarization temperature Td, however, it increases the Curie temperature Tc. In contrast, Td and Tc are shifted towards a higher temperature with increasing amount of BLT. BNT–BKT–BLT ceramics show typical ferroelectric features at room temperature. The addition of BKT increases the remnant polarization Pr and lowers the coercive field Ec significantly. The polarization–electric field (P–E) hysteresis loops at different temperatures reveal that the loops deform at a high temperature as a result of the phase transition from ferroelectric to antiferroelectric during the heating process, so that d33 diminishes rapidly.