Papers by Keyword: Bismuth Sodium Titanate (BNT)

Abstract: This study investigated the influence of excess Bi₂O₃ and Na₂CO₃ on the crystal structure, microstructure and dielectric properties of (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics. The BNT ceramics were synthesized using the solid-state reaction method with various excess Bi₂O₃ and Na₂CO₃ levels (0, 1, 2, 3 and 4 mol%). The X-ray characterization revealed that all samples had a rhombohedral structure. A pure perovskite phase was obtained in all samples. The lattice parameter a tended to increase with increased excess Bi₂O₃ and Na₂CO₃ content in the calcined powders and sintered ceramics. The average particle size increased while, the average grain size tended to decreased with increased of excess Bi₂O₃ and Na₂CO₃ content. The depolarization temperature (T_d) and the Curie temperature (T_c) were slightly decreased with the increase of excess Bi₂O₃ and Na₂CO₃ content. The dielectric properties were related to the density.

Abstract: In this work, Praseodymium (Pr) doped bismuth sodium titanate, (Bi0.5Na0.5)TiO3 (BNT) is successfully produced using the soft combustion technique. The effects of Pr doping on stoichiometry, microstructure, density and dielectric properties are studied. Pure phase can be obtained in all samples containing 0, 5, 10 and 20% Pr after calcination at 800°C for three hours. The powders are then pressed into pellets and sintered at 1050°C for three hours. The crystallite size and grain size decrease with increasing Pr amount because Pr acts as grain growth inhibitor. Maximum density is obtained in 5% Pr doped BNT, beyond which density decreasing. Maximum dielectric constant of 756 was obtained in 5% Pr doped BNT and decreases beyond that. Pr doped in BNT also causes dielectric loss to decrease. The result is in agreement with structural, microstructure and density analysis.

Abstract: 0.995(Bi1/2Na1/2)TiO3-0.005Bi(B’,B”)O3 solid-solution ceramics (B’,B” denote Zn, Mg, Ni, Ti, Nb) were fabricated and their ferroelectric properties were investigated. Based on the structural characteristics of Bi(B’,B”)O3 analyzed by first-principles calculations, a materials design for obtaining a large piezoelectric strain is proposed: an index Z= Ps∙(ε33*∙s33)1/2, where Ps is spontaneous polarization, ε33* is relative permittivity and s33 is elastic compliance. A positive correlation was observed between Z and effective piezoelectric constant d33* observed for strain measurements.

Abstract: Single crystals of x (Bi0.5K0.5)TiO3-(1-x)(Bi0.5Na0.5)TiO3 (BKT-BNT) solid solution were grown by a flux method, and their ferroelectric properties were investigated along [100]cubic (the cubic notation). While the flux growth soaked at 1250 °C led to the crystals with a composition of x less than 0.14, the crystals with x of 0.45 were obtained by decreasing soaking temperature to 1150 °C. The crystals of BKT-BNT (x = 0.45) exhibited a relatively large remanent polarization of 39  C/cm2 and a low coercive field of 23 kV/cm.

Abstract: 0.999Bi0.5Na0.5TiO3-0.001BaTiO3 (BNT-0.1%BT) single crystals with a maximum size of 1×1×1 mm3 were successfully grown by a flux method using BNT-6%BT powder and Bi2O3 as a flux. The crystals showed a remanent polarization of 33 μC/cm2 and coercive electric field of 40 kV/cm along [100]Cubic. Electric-field induced strain measurements along [100]Cubic revealed an effective piezoelectric strain constant d33 * of 80 pm/V.

Abstract: (1-x)(Bi1/2Na1/2)TiO3-xBiAlO3 [BNTA100x (0 ≤ x ≤ 0.14)] ceramics were prepared by a conventional ceramic fabrication process. Single-phase perovskite structures were formed when x ≤ 0.08 for BNTA100x. The depolarization temperature, Td, at which piezoelectricity disappears, decreased with increasing x. The piezoelectric constant, d33, increased with increasing x because of the increase in free permittivity accompanied with decreasing Td. d33 and the electromechanical coupling factor, k33, of BNTA6 were 93 pC/N and 0.41, respectively. Normalized strain d33* (= Smax/Emax) at 60 kV/cm at the maximum field-induced strain was 122.2 pm/V for BNTA8. The value of d33* was higher than the calculated value of d33.

Abstract: The factor determining texture development was examined for Bi0.5Na0.5TiO3 ceramics made by the reactive-templated grain growth process using platelike Bi4Ti3O12 particles as reactive template. Platelike, skeleton Bi0.5Na0.5TiO3 particles were formed by the reaction between Bi4Ti3O12 and Na2CO3 in calcined compacts. Coalescence of small grains in the skeleton particles to form single template particles was important to obtain highly textured ceramics.

Abstract: The phase transition temperatures of divalent and trivalent ions substituted (Bi1/2Na1/2)TiO3 ceramics were investigated in detail by electrical measurement. BNT ceramics substituted by divalent (Ca2+, Sr2+ and Ba2+) and trivalent (La3+, Nd3+, Ho3+ and Yb3+) ions were prepared by conventional ceramic fabrication process. For these ceramics, the depolarization temperature, Td, the rhombohedral-tetragonal phase transition temperature, TR-T, and the temperature of the maximum dielectric constant, Tm, were determined on the basis of the temperature dependences of dielectric and piezoelectric properties. In this study, we demonstrated the relationship between phase transition temperature and ionic radius of ions substituted in the A-site of BNT ceramics.

Abstract: Lead-free (1-x) Bi1/2Na1/2TiO3-xKNbO3 (x=0, 0.01, 0.02, 0.04, 0.05 0.06, 0.10) piezoelectric ceramics were prepared by conventional ceramics fabrication technique. The results of x-ray diffraction (XRD) show that these ceramics possess pure perovskite structures with a symmetry transition from rhombohedral to cubic at about x = 0.05. The piezoelectric properties of these ceramics were reported and found to reach extreme values at x = 0.04 with d33 up to 113pC/N and kp up to 22%. The temperature dependence of dielectric constant and dielectric loss of these ceramics were also investigated. The Curie temperature and depolarization temperature dropped with the increase of KNbO3 amount.

Abstract: Lead-free piezoelectric ceramics based on bismuth sodium titanate (BNT) -barium hafnate titanate (BHT) were prepared by a two-step synthesis process. The final BNT-BHT ceramics sintered at 1180oC for 2 h in air showed a perovskite structure with high density. The morphotropic phase boundaries (MPB) were found in BNT based piezoelectric ceramics with 8~10 wt% BHT in composites. In the case of Bi0.5Na0.5TiO3-0.08BaHf0.05Ti0.95O3 ceramics, a maximum piezoelectric coefficient d33 of 122.6 pC/N was obtained. The remnant polarization (Pr) and coercive field (Ec) were measured and the relationship between ferroelectricity and the BHT fraction in the compounds was investigated. The BNT-BHT ceramics were expected to be a new and promising candidate for lead-free piezoelectric device applications.