Key Engineering Materials Vols. 512-515

Abstract: The ferroelectricity of Bi_3.25Sm_0.75Ti₃O₁₂ (BST), and Bi_3.25Sm0_.75Ti_2.97V_0.03O₁₂ (BSTV) ceramics prepared at 1100°C by a conventional ceramic technique was investigated. These ceramics possess random-oriented polycrystalline structure. The remanent polarization (Pr) and coercive field (Ec) of the BST ceramics are 16 µC/cm² and 64kV/cm, respectively. Furthermore, V substitution improves the Pr value of the BST ceramics up to 25 μC/cm², which is much larger than that of the BST ceramics. Therefore, co-sustitution of Sm and V in is effective for the improvement of the ferroelectricity of Bi₄Ti₃O₁₂ ceramic.

Abstract: Based on piezoceramic stack actuators, a stage (dimension of 50mm×50mm×11mm) with a symmetric displacement magnifying mechanism is studied in this paper. FEM simulations are carried out to reveal the performance of the micropositioning stage and the amplification radio of the flexure hinge is 4.76. The working mode of the flexure hinge of the stage is also simulated by finite element method, and its natural frequency is 3291Hz. A series of tests about piezoceramic stack actuators have been done, including static, dynamic and temperature tests. The experimental results are identical to the theoretical analysis and give help to the application of piezoceramic stack actuators. It can also help the precise micropositioning stage driven by PZT to achieve higher positioning accuracy and resolution.

Abstract: The 0-3 and 1-3 composites have been widely used to produce various kinds of piezoelectric devices. This article focuses on the damping properties of the epoxy/piezoelectric composites. Due to the piezoelectric effect, the composites are expected to improve the damping properties and can be used in the field of vibration reduction and noise control. Two piezoelectric materials were embedded into the epoxy resin to make specimens, T-ZnOw/epoxy resin as 0-3 and PZT fibers/epoxy resin as 1-3 composite. With the method of dynamic mechanical analysis, the temperature dependence of the mechanical storage modulus and the loss factor (tanδ) were measured at different frequencies. The experimental results clearly show that the loss factor increases when testing frequency is higher. In this study, the piezoelectric damping and the viscoelastic effect are discussed and both of them contribute to the damping property of the composite system.

Abstract: By a novel freeze-casting technique, PZT ceramics with unidirectional pore channel structure were fabricated using tert-butyl alcohol (TBA) as pore forming template, PVB as adhesive, and arabic gum as dispersing agent. The solid loading in the initial slurry varied from 15 vol.% to 40 vol.%. The porous structure can be controlled by the freezing temperature condition which was chosen by dry ice (-78°C). The sintered PZT ceramics with a high porosity showed high piezoelectric coefficient. The d₃₃ value of some samples with the porosity 26% was larger than the dense PZT ceramics which was 690 pC/N. Meanwhile, pore morphology of the porous PZT ceramics was observed with SEM and analyzed changing with the solid loading of PZT in slurry. In addition, the influences of solid loading in PZT slurry on piezoelectric and dielectric properties of the porous PZT ceramics were discussed from a theoretical perspective.

Abstract: Extending the investigations on (Na0.5K0.5)NbO3-based solid solution for lead-free piezoelectric ceramics, this paper consider the complex solid-solution system (Na0.5K0.5)NbO3–Bi0.5(Na0.93K0.07)0.5TiO3 [NKN-BNKT]. (Na0.5K0.5)NbO3 with 2 ~ 6 mol% Bi0.5(Na0.93K0.07)0.5TiO3 has been prepared following the conventional mixed oxide process. A morphotropic phase boundary (MPB) between orthorhombic (O) and rhombohedral (R) was found at the composition 0.98NKN-0.02BNKT with correspondingly enhanced dielectric and piezoelectric properties. The electromechanical coupling factor and dielectric constant are higher for compositions near the MPB. The dielectric constant (KT33), planar coupling coefficient (kp) and thickness coupling coefficient (kt)of 0.98NKN-0.02BNKT ceramics were 1040, 47% and 48%, respectively.

Abstract: The introduction of lithium ion into BNT-BKT-BT ceramics with sol-gel method allows the development of high-performance lead-free piezoelectric ceramics. Nanoscale precursor powders were synthesized through calcination of amorphous gels, and densified ceramics with single perovskite structure were prepared at a relatively low sintering temperature 1110 °C. Crystal grain growth was fully developed with the Li+ addition through scanning electron microscope observation. Enhanced electrical properties, piezoelectric constant d33~184 pC/N and planar electromechanical coupling factor kp~0.30, were obtained for the ceramics.

Abstract: Piezoelectric barium zirconate-titanate ceramic nanofibers were prepared by combination of Sol-Gel processing and electrospinning technique. The average diameter of barium zirconate-titanate ceramic nanofibers is nearly 200 nm. The x-ray diffraction pattern of the fibers showed that their crystalline structures displayed tetragonal perovskite structures. Interdigitated electrodes were sprayed on an epoxy resin substrate. BaTi_0.9Zr_0.1O₃ nanofibers were then aligned on the interdigitated electrodes and covered with the solution of epoxy resin, so as to obtain Piezoelectric Fiber/polymer Composites. The periodic output voltages with maximum value of 0.26V were obtained under harmonic excitation, by using a finger to apply a dynamic load on the top of the composites.

Abstract: Dielectric and piezoelectric properties of ceramic solid solutions based on the compositions close to the MPB in the system (1-x)BiScO3 – xPbTiO3 (x- 0.63, 0.635, 0.64) have been studied. The 1st order phase transitions were observed at temperatures near 700 K. Increase in the lead titanate content stimulates slight increase in the TC value. Cr2O3 additives in amounts up to 0.2 w. % favor to the decrease of total conductivity and dielectric loss at high temperatures. Increase in the d33 and kt piezocoefficients was observed in modifed ceramic. Besides peaks in temperature dependences of dielectric permittivity and dielectric loss marked ferroelectric to paraelectric phase transitions, effects of dielectric relaxation, determined by oxygen vacancies were revealed.

Abstract: Calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is a high Curie temperature (Tc) piezoelectric material, however, their piezoelectric properties are very poor. In order to improve the piezoelectric performance of CBN, the Eu modification and texture method (templated grain growth, TGG) were applied in this material system. The piezoelectric properties of CBN ceramics were significantly enhanced by Eu modification. The 5mol% Eu dopants in CBN ceramics have a higher piezoelectric constant and higher Tc (d₃₃=12.8pC/N, Tc=945°C) than that of undoped CBN ceramics (d₃₃=6.2pC/N, Tc=930°C). Highly textured 5mol% Eu doped CBN ceramics with 92% Lotgering factor were obtained by the TGG technique. The piezoelectric properties of textured and modified CBN ceramics are anisotropic on different directions of perpendicular (d₃₃=0.1pC/N) and parallel (d₃₃=20.5pC/N) to tape stacking direction. Furthermore, they had excellent thermostable piezoelectric properties from room temperature to near Curie temperature. The textured Eu modified CBN ceramics with high Tc and high piezoelectric properties might be a promising candidate for high-temperature piezoelectric applications.

Abstract: Lead-free potassium sodium niobate ceramic thin films were synthesized using rf magnetron sputtering technology for MFIS structures. The optimal sputtering parameters of the as-deposited KNN thin films for depositing times of 1h were obtained. Regarding the measured physical properties, the micro-structure and thickness of as-deposited KNN thin films for different oxygen concentration were obtained and compared by XRD patterns and SEM images. The surface roughness of KNN thin film was also observed by AFM morphology. The average grain size and root mean square roughness were 250 and 7.04 nm, respectively. For KNN thin films in the MFIS structure, the capacitance and leakage current density were 280 pF and 10^-8A/cm², respectively. We investigated that the leakage current density and the memory window increased, the capacitance critically increased as the oxygen concentration increased from 0 to 40%. However, the excess oxygen concentration process was decreased the electrical and physical of as-deposited KNN thin film. The effect of oxygen concentration on the physical and electrical characteristics of KNN thin films was investigated and determined.