Papers by Keyword: BNT

Abstract: The properties of modified Bi_0.5Na_0.5TiO₃ (BNT) based lead-free ceramics were investigated. The BNT-based ceramics were prepared by a solid-state mixed oxide method Phase formation was determined by X-ray diffraction technique (XRD). The X-ray diffraction analysis of the ceramics suggested that all samples exhibited a perovskite structure without second phase. The value of dielectric constant increased with increasing in sintering temperature. Moreover, high sintering temperatures could improve ferroelectric properties of BNT base lead-free ceramics.

Abstract: The properties of modified Bi_0.5Na_0.5TiO₃ (BNT) based lead-free ceramics were investigated. The BNT-based ceramics were prepared by a two-steps sintering method. The ceramics were sintered at T₁=1373 K and T₂= 1173 K for various dwell times (0, 2, 4, and 8h). The properties of the ceramics were characterized by many techniques. The ceramic samples exhibited a pure perovskite phase with rhombohedral symmetry. The microstructural analysis by a scanning electron microscopy (SEM), indicated that all ceramics had a similar microstructure. Piezoelectric and mechanical properties of the ceramics were improved at a suitable dwell time at T₂.

Abstract: Perovskite-structured (Bi_1/2Na_1/2)TiO₃ (BNT) ferroelectric with Curie temperature about 320°C is considered to be a good candidate of high temperature lead-free materials with a positive temperature coefficient of resistance (PTCR). In this study, lead-free PTCR ceramics with compositions of (1-x)BaTiO₃-x(Bi_1/2Na_1/2)TiO₃ (BT-BNT x=0.5-55mol%) were successfully prepared without any additional donor or acceptor dopants. The effects of BNT content on the Curie temperature T_c and the PTC effect of the ceramic materials were investigated. The X-ray diffraction data indicated that BT phase and BNT phase formed a solid solution during sintering even though the x value was up to 55mol%. The Curie temperature T_c of the samples increased from ~130°C to ~216°C with the increase of the BNT amount (x value) from 0.5mol% to 40mol%. However, it decreased when excess BNT was added (x value increased from 40mol% up to 55mol%), which was resulted from the volatile effects of Bi³⁺ and Na⁺ ions during sintering. The sample of 0.6BaTiO₃- 0.4(Bi_1/2Na_1/2)TiO₃ with T_c =216°C, room-temperature resistivity 10⁴ Ω·cm and R_max/R_min= 10^2.7 was obtained. There is a relationship between the Curie temperature and the cell volume of the perovskite structured lattice.

Abstract: In this research work, the investigation of the morphotropic phase boundary, physical properties and electrical properties of lead- free piezoelectric materials of bismuth sodium titanium oxide: (Bi0.5Na0.5)TiO3 (BNT) and potassium niobium oxide : KNbO3 (KN) in the ceramic system of (1-x)BNT- xKN where x= 0.00, 0.03, 0.05, 0.08, 0.10 and 0.15 by modified mixed oxide method was carried out. The BNT and KN powders were prepared separately using calcination technique with optimum calcination temperature for producing both BNT and KN powders of about 800°C. XRD results revealed that the BNT-KN ceramics with low KN content of x less than 0.05 contain ferroelectric perovskite phase with rhombohedral symmetries while the higher KN content ceramics have mixed symmetries between rhombohedral and orthorhombic. From the evidences including phases, microstructures and dielectric data of the BNT-KN ceramics, it may be assumed that the morphotropic phase boundary may be at around the composition of x = 0.05.

Abstract: In this research, 0-3 composites between non-lead based piezoceramic and polymer were fabricated using the suction technique. Bismuth sodium titanate (Bi0.5Na0.5TiO3:BNT) which prepared from conventional mixed oxide method was used as active phase whereas epoxy resin was used as matrix phase. The 50% volumetric fraction of BNT/epoxy resin can obtain from suction technique. The physical and piezoelectric properties of composites samples were examined. It can be found that density of composite samples were about 1.78 g/cm3. Moreover, the piezoelectric coefficient (d33) of sample was 13 pC/N. Furthermore, the microstructure of composites was determined using SEM technique.

Abstract: Zirconium-doped bismuth sodium titanate ceramics were prepared using the conventional processing method. X-ray diffraction analysis indicated the materials were single phase with a systematic shift due to increased unit cell size. The measured densities and grain size of the ceramic samples were found to range from 5.79-6.03 g/cm3 and 0.5-1.6 µm, respectively. The dielectric constant as a function of temperature became broader as Zr content increased. The piezoelectric constant was found to decrease with increasing Zr. Within the range of the solid solutions investigated, the materials seem to be promising for high temperature applications where stable dielectric constant is required.

Abstract: Thin films of lead-free piezoelectric ceramics (Bi1/2Na1/2)TiO3 (abbreviated as BNT) were prepared on pure titanium substrates by a hydrothermal method. Several properties of BNT films synthesized in various Bi3+ and Ti4+ concentrations of starting materials were investigated using SEM, EDX, XRD and other instruments. Moreover, the effects of ion concentrations of starting materials on permittivity and piezoelectric effect of BNT films were discussed. The Bi2O3 crystals were more deposited on the surface of films with the increase of the concentration of Bi3+. The relationship between the deflection and applied electric field was measured on unimorph cantilever type actuators made from three samples which had different XRD patterns. The results showed that the piezoelectric effect of BNT films was dependent on the crystallization level of BNT.

Abstract: Ferroelectric properties of (Bi1/2Na1/2) TiO3-SrTiO3 were studied. The dielectric properties were measured at 1KHz. It was found that the dielectric constants are improved with the increase of additive amount of BNT. If the amount continues increasing, the properties become worse, the optimum dielectric constant of the samples can reach 4300. When the proportion of (Bi1/2Na1/2)TiO3: SrTiO3 is 65:35, with the increase of additive amount of MnCO3, the Curie temperature descends obviously. The dielectric constant increased at beginning and dropped sharply when the amount of MnCO3 exceeds 1.1wt%.

Abstract: (Na0.5Bi0.5)TiO3 (Abbreviated to BNT) was synthesized by hydrothermal process and the average gain size was 15 nm with narrow size distribution. Pure perovskite structure of BNT particles was identified by XRD analysis. The nanoscale BNT powder was selected as raw material to fabricate BNT based ceramics with BaTiO3 (Abbreviated to BT) and Ba(Cu0.5W0.5)O3 (Abbreviated to BCW) doping. SEM images show that the ceramic using nanoscale BNT powder as raw material has a high dense body with the average gain size from 0.5 μm to 1 μm. The experimental results show that with increasing amount of BCW, d33 and Kp of (0.94-x)BNT-0.06BT-xBCW increase initially, then reach the maximum values of 130 pC/N and 0.32 when 5mol% of BCW was added. Further increasing amount of BCW leads to decreasing d33 and Kp. The optimal piezoelectric and dielectric properties were obtained as d33 = 130 pC/N, Kp = 0.32, εr = 800, tgδ = 0.06.