Fabrication of combined 0–3 and 1–3 connectivities PZT/epoxy resin composites

PZT/epoxy resin composites of combined 0–3 and 1–3 connectivities were fabricated, for the first time, using suction, dice and fill techniques. Two types of composites (PZT(m)/epoxy resin and PZT(sp)/epoxy resin) were produced using PZT powders prepared by mixed oxide and spray-drying methods. Physical, mechanical, dielectric and piezoelectric properties of the composites were examined. Generally, overall results between the two composites were found to be very similar (volumetric changes ∼34–37%, d₃₃∼20.2–25.3 pC/N, K_p∼0.54–0.61). Higher density was found in PZT(sp)/epoxy resin, however, due to better packing of particles. Moreover, both PZT/epoxy resin composites exhibited very low acoustic impedance (Z∼4.12–4.84 Mrayls), which is very close to that of human tissue and water. Therefore, these new composites may be suitable for use in medical applications. PACS 81.05.Qk; 81.05.Zx; 77.87.-s     

Structural and electrical properties characterization of (1–x)PbZr0.52Ti0.48O3–xBaFe0.5Nb0.5O3 system

The structural and electrical properties of (1-x)PbZr_0.52Ti_0.48O₃–xBaFe_0.5Nb_0.5O₃ ceramics system with the composition near the morphotropic phase boundary were investigated as a function of the BaFe_0.5Nb_0.5O₃ content by X-ray diffraction (XRD) and dielectric measurement technique. Studies were performed on the samples prepared by solid state reaction for x=0.1, 0.2, 0.3, 0.4 and 0.5. The XRD analysis demonstrated that with increasing BFN content in (1-x)PZT–xBFN, the structural change occurred from the tetragonal to the cubic phase at room temperature. Changes in the dielectric behavior were then related to these structural depending on the BFN content. PACS 77.84.Dy; 77.22.Ch; 77.22.Gm     

Phase evolution and effect of pre-heating temperature on the characteristics of PZT thin films grown by using a triol sol--gel route

Lead zirconate titanate (PZT) films were fabricated on Pt(111)/Ti/SiO₂/Si(100) using the triol sol--gel method. The effect of the pre-heating temperature on the phase transformations, microstructures, electrical properties and ferroelectric properties of the PZT thin films was investigated. Randomly-oriented PZT thin films pre-heated at 400°C for 10?min and annealed at 600°C for 30?min showed well-defined ferroelectric hysteresis loops with a remanent polarization of 26.57?µC?cm^?2 and a coercive field of 115.42?kV?cm^?1. The dielectric constant and dielectric loss of the PZT films were 621 and 0.0395, respectively. The microstructures of the thin films are dense, crack-free and homogeneous with fine grains about 15–20?nm in size.     

Enhancement of DNA hybridization under acoustic streaming with three-piezoelectric-transducer system

Recently, we have demonstrated that DNA hybridization using acoustic streaming induced by two piezoelectric transducers provides higher DNA hybridization efficiency than the conventional method. In this work, we refine acoustic streaming system for DNA hybridization by inserting an additional piezoelectric transducer and redesigning the locations of the transducers. The Comsol? Multiphysics was used to design and simulate the velocity field generated by the piezoelectric agitation. The simulated velocity vector followed a spiral vortex flow field with an average direction outward from the center of the transducers. These vortices caused the lower signal intensity in the middle of the microarray for the two-piezoelectric disk design. On the contrary, the problem almost disappeared in the three-piezoelectric-disk system. The optimum condition for controlling the piezoelectric was obtained from the dye experiments with different activation settings for the transducers. The best setting was to activate the side disks and middle disk alternatively with 1 second activating time and 3 second non-activating time for both sets of transducers. DNA hybridization using microarrays for the malaria parasite Plasmodium falciparum from the optimized process yielded a three-fold enhancement of the signal compared to the conventional method. Moreover, a greater number of spots passed quality control in the optimized device, which could greatly improve biological interpretation of DNA hybridization data.     

The effect of Zr content on electrical properties of Ba(Ti<Subscript>1-x</Subscript>Zr<Subscript>x</Subscript>)O<Subscript>3</Subscript> ceramics

The effect of Zr content on the crystal structure and electrical properties of barium zirconate titanate (Ba(Zr,Ti)O₃) was studied by X-ray diffraction and dielectric, ferroelectric and impedance spectroscopy. An increase of Zr content into BaTiO₃ leads to a reduction in its c-parameter and an increase in its a-parameter, resulting in a change from tetragonal to cubic symmetry of the BaTiO₃ unit cell. The Curie temperatures are lowered and the relative permittivity values are decreased with increasing Zr content. The presence of BaZrO₃ secondary phases has the affect of decreasing tanδ. A higher applied electric field is required during the polarization process because of the effect of domain-wall pinning caused by oxygen vacancies. Impedance spectroscopy studies of Ba(Ti_0.95Zr_0.05)O₃ ceramics show a decrease in the bulk resistance with increasing temperature, indicating a typical negative temperature coefficient of resistance. PACS 74.62.Bf; 74.62.Yb; 77.22.Ch; 77.80.Bh; 77.84.Dy     

Influence of B2O3 on electrical properties and phase transition of lead-free Ba(Ti0.9Sn0.1)O3 ceramics

The phase transition and electrical properties of Ba(Ti_0.9Sn_0.1)O₃ ceramics with B₂O₃ added were investigated to explore the effect of B₂O₃ addition on enhanced densification and dielectric constant of these ceramics. With increasing B₂O₃ content, a linear reduction of ferroelectric to paraelectric transition temperature was observed. In addition, higher B₂O₃ concentrations enhanced a ferroelectric relaxor behavior in the ceramics. Changes in this behavior were related to densification, second-phase formation and compositional variation of the ceramics.     

Impedance study of giant dielectric permittivity in BaFe0.5Nb0.5O3 perovskite ceramic

Single-phase BaFe_0.5Nb_0.5O₃ (BFN) ceramics were prepared by solid-state reaction method and were characterized by X-ray Diffraction (XRD) technique. Then, impedance spectroscopy measurements were conducted in a frequency range from 100 Hz to 1 MHz and in a temperature range from 293 to 600 K. Relaxation phenomena of non-Debye type have been observed in the BFN ceramics, as confirmed by the Cole–Cole plots. The higher values of ε′ at the lower frequencies are explained on the basis of the Maxwell–Wagner (MW) polarization model. Complex impedance analysis enables us to separate the contributions from grains and grain boundaries of our samples. We found that at higher temperatures grain boundary resistance is higher than grain resistance, irrespective of composition.     

Sol–gel synthesis and characterization of BaTi2O5 powders

BaTi₂O₅ powders were synthesized using a sol–gel method and characterized. Phase evolution and characteristics of the samples were studied using differential scanning calorimetry, thermogravimetric analysis and X-ray diffractometry. The results show that the formation of BaTi₂O₅ starts around 800 °C and continues until 1200 °C in air, and in this calcination temperature range all powders appear to be single-phase monoclinic BaTi₂O₅. The mechanism of BaTi₂O₅ formation was studied by Fourier-transform infrared spectroscopy. The infrared absorption peaks confirm the existence of a substitution reaction with the chelating reagent corresponding to different modes of vibration characteristic of the acetate group. Scanning electron microscopy observations reveal that the size of the particles that are nearly round in shape formed due to agglomeration is about 0.1–1.5 μm and increases with calcination temperature. PACS 81.70.Pg; 81.20.Fw; 77.84.Dy; 61.10.Nz; 33.20.Ea     

Properties of Sr- and Sb-doped PZT–Portland cement composites

Lead zirconate titanate (PZT) ceramic-cement-based composites have increasingly been recognized as an attractive new composite material for use as a sensor in structural applications. In this work, PZT was doped with Sr and Sb (PSZT) to give it greater dielectric constant (ε _r) and higher piezoelectric coefficient (d ₃₃) values than normal PZT and is the first time that it is mixed with normal Portland cement to produce a 0–3 connectivity PSZT–Portland cement composite using PSZT contents of 50% and 70% by volume. Scanning electron micrographs show PSZT ceramic particles closely surrounded by the hydrated cement matrix where a dense microstructure can be observed in the interfacial zone. Both the ε _r and d ₃₃ values were found to increase with PSZT content and the values are amongst the highest so far for these types of composites, where the ε _r and d ₃₃ values reached 590 and 48 pC/N, respectively.     

Dielectric and impedance measurements on (1−x)Ba(Fe1/2Ta1/2)O3-xBa(Zn1/3Ta2/3)O3 ceramics

In this work, ((1−x)Ba(Fe_1/2Ta_1/2)O₃-xBa(Zn_1/3Ta_2/3)O₃), ((1−x)BFT-xBZT) ceramics with x = 0.00–0.12 were synthesized by the solid–state reaction method. X-ray diffraction data revealed that both the powders and ceramics were of a pure-phase cubic perovskite structure. All ceramics showed large dielectric constants. For the x = 0.12 sample, a very high dielectric constant (>20,600) was observed. A lowering in the dielectric loss compared to pure BFT ceramics was observed with the BZT addition. The impedance measurements indicated that BZT has a strong effect on the bulk grain and grain boundary resistance of BFT ceramics. These results are in agreement with the measured dielectric properties. Based on dielectric and impedance results, (1−x)BFT-xBZT ceramics could be of great interest for high performance dielectric materials applications due their giant dielectric constant behavior.