Effect of MnO on the Phase Development, Microstructures, and Dielectric Properties of 0.95Na0.5K0.5NbO3–0.05LiTaO3 Ceramics

Lead-free piezoelectric ceramics in the system 0.95Na_0.5K_0.5NbO₃–0.05LiTaO₃ were modified with ≤1 mol% MnO. Maximum densities occurred at a sintering temperature of 1050°C. Characteristic changes in the relative intensity of X-ray diffraction peaks were consistent with Mn ions substituting on the perovskite lattice to produce a change from orthorhombic to a mixture of tetragonal and orthorhombic phases. Grain growth during secondary recrystallization was also affected, leading to increased grain sizes. The dielectric constant increased from ∼600 in unmodified ceramics to ∼1040 in ceramics prepared with 0.5 mol% MnO.     

Influence of Copper Nanoparticles Concentration on the Properties of Poly(vinylidene fluoride)/Cu Nanoparticles Nanocomposite Films

In this study, the nanocomposite films of polyvinylidene fluoride/copper nanoparticles were prepared by mixing of copper nanoparticles in a solution of dimethylformamide and polyvinylidene fluoride. The prepared nanocomposites were investigated by fourier transform infrared spectroscopy and X-ray diffraction techniques, showed an obvious α- to β-phase transformation compared to pure PVDF. Scanning electron microscope micrographs showed spherulitic crystal structure of PVDF. The spherulitic morphology of the pure PVDF is maintained for the PVDF nanocomposites; the size of the spherulites decreased by increasing weight fraction of copper nanoparticles. The optical band gap values deduced from the UV–Visible absorption spectra were found to reduce from 4.77 eV in pure PVDF to 3.2 eV after embedding 1 wt% of copper nanoparticles. The surface resistivity values were decreased with increasing copper nanoparticles content. Thermal stability of the nanocomposites was studied by thermogravimetric analysis (TGA). TGA curves showed that nanocomposite films have higher resistance to thermal degradation compared to pure PVDF.     

Dependence of photocatalytic activity on structural and optical properties of nanocrystalline ZnO powders

Nanocrystalline ZnO powders were prepared from cetyltrimethylammonium bromide (CTAB)-modified NaOH, NH₄OH and (CH₂)₆N₄ solutions. The calcined ZnO powders exhibited a hexagonal structure without any secondary phase. Different shapes of ZnO powders were formed depending on CTAB concentration and type of precipitating agent. As (CH₂)₆N₄ solution was used, rod-like ZnO structure was changed to a spherical shape when CTAB concentration was increased. The widest E_g value of approximately 3.23 eV was obtained from the sample containing the lowest defect concentration. The decolorization efficiency was higher than 90% after irradiating for 90 min and the sample with higher E_g value showed higher decolorization efficiency.     

Structural and electrical properties of Na0.47K0.47Li0.06NbO3 lead-free piezoelectric ceramics modified by AgSbO3

(1?x)Na_0.47K_0.47Li_0.06NbO₃ (NKLN)–xAgSbO₃ lead-free piezoelectric ceramics were prepared using a reaction sintering method. The effects of AgSbO₃ doping on the structural and electrical properties of NKLN ceramics sintered at 1000–1040 °C were studied. The dopant affected densification, phase content, sintering temperature, microstructure and electrical properties. Variations in the relative intensity of X-ray diffraction peaks were consistent with Ag⁺ and Sb⁵⁺ ions substituting on the perovskite lattice to produce a change in the proportions of co-existing tetragonal and orthorhombic phases. Grain growth during secondary re-crystallization was also affected. The temperature of the orthorhombic–tetragonal (O–T) phase transition and the Curie temperature (T_C) decreased as a result of AgSbO₃ modifications. The dielectric and piezoelectric properties are enhanced for the composition near the orthorhombic–tetragonal polymorphotropic phase boundary. The 0.92Na_0.47K_0.47Li_0.06NbO₃–0.08AgSbO₃ ceramics exhibited optimum electrical properties (d₃₃=252 pC/N, ε_r=1450, tan δ=0.02, and T_C=280 °C). These results reveal that (1?x)Na_0.47K_0.47Li_0.06NbO₃–xAgSbO₃ ceramics are promising materials for lead-free piezoelectric application.     

Reaction-sintering of lead-free piezoceramic compositions: (0.95 − x)Na0.5K0.5NbO3–0.05LiTaO3–xLiSbO3

Incorporation of LiSbO₃ into the lead-free piezoceramic composition 0.95Na_0.5K_0.5NbO₃–0.05LiTaO₃ produced a change from an orthorhombic to tetragonal crystal system in samples produced by reaction-sintering. The inferred limit of solid solution along the compositional join, (0.95 − x)Na_0.5K_0.5NbO₃–0.05LiTaO₃–xLiSbO₃, occurred at x ~ 0.06. Differential scanning calorimetry indicated broad peaks at temperatures associated with ferroelectric–paraelectric transitions. The transition temperatures decreased with increasing values of x, up to x = 0.06. Microstructures showed secondary grain growth; a slight decrease in grain-size with increasing LiSbO₃ modification was identified.     

Design and performance testing of an ultrasonic linear motor with dual piezoelectric actuators

In this work, design and performance testing of an ultrasonic linear motor with dual piezoelectric actuator patches are studied. The motor system consists of a linear stator, a pre-load weight, and two piezoelectric actuator patches. The piezoelectric actuators are bonded with the linear elastic stator at specific locations. The stator generates propagating waves when the piezoelectric actuators are subjected to harmonic excitations. Vibration characteristics of the linear stator are analyzed and compared with finite element and experimental results. The analytical, finite element, and experimental results show agreement. In the experiments, performance of the ultrasonic linear motor is tested. Relationships between velocity and pre-load weight, velocity and applied voltage, driving force and applied voltage, and velocity and driving force are reported. The design of the dual piezoelectric actuators yields a simpler structure with a smaller number of actuators and lower stator stiffness compared with a conventional design of an ultrasonic linear motor with fully laminated piezoelectric actuators.     

Determination of piezoelectric and pyroelectric coefficients and thermal diffusivity of 1-3 PZT/epoxy composites

PZT/epoxy composites with 1-3 connectivity were prepared using the dice-and-fill technique. The samples were poled with an electric field of 10 MV/m for 30 minutes at room temperature. The piezoelectric and pyroelectric coefficients for the composites were measured. From the laser interferometric measurements, it was found that the piezoelectric d/sub 33/ coefficients for the composites were independent of the volume fraction and averaged (190 /spl mnplus/ 10) pm/V, which was about half of the measured value of lead zirconate titanate (PZT) ceramic. Measurements of the pyroelectric coefficient showed that the coefficients increased with the ceramic content and reached values as large as 54 /spl mu/C/m/sup 2/ /spl deg/C. The thermal diffusivity of the composites was also determined using a technique based on the measurement of the phase retardation of a thermal wave passing through the material. The average value for the composites was (2.15/spl mnplus/ 0.05) /spl times/ 10/sup -7/ m/sup 2//s.     

Microstructure and ferroelectric properties of sol–gel graded PZT (40/52/60) and (60/52/40) thin films

Graded Pb(Zr_x,Ti_1−x)O₃ films with Zr compositions varied across the thickness direction were deposited on Pt/Ti/SiO₂/Si substrate using a conventional spin-coating method. The up- and down-graded PZT films exhibited the perovskite polycrystalline structure. Microstructure investigations of the films showed a dense texture and successive layers of different compositions. The relative permittivities of the up- and down-graded PZT films measured at 1 kHz and room temperature were 1846 and 1019, respectively. Good dielectric and ferroelectric properties as well as the low-temperature processing suggested that the compositionally graded PZT films were promising for memory device applications.     

Optical and photocatalytic properties of La-doped ZnO nanoparticles prepared via precipitation and mechanical milling method

The synthetic method used for preparing ZnO nanoparticles strongly influenced the products obtained. The ZnO powders incorporated more La when prepared by the mechanical milling method whereas the La₂O₃/ZnO composite nanoparticles were formed better using the precipitation method. The phase formations were detected by the X-ray diffraction technique and the morphology of the samples was followed by scanning electron microscopy. The La contents affected the crystallite size. This was explained by the formation of LaOZn on the surface of the samples and by the Zener pinning effect. The band gap energy of the samples was influenced by repulsion between the valence and conduction bands and the presence of a secondary phase. The photocatalytic degradation of a methylene blue solution by the samples depended upon the number of oxygen vacancies.     

Effect of Calcination Conditions and Excess Alkali Carbonate on the Phase Formation and Particle Morphology of Na0.5K0.5NbO3 Powders

Sodium-potassium niobate [Na_0.5K_0.5NbO₃] powders were prepared following the conventional mixed oxide method. An orthorhombic XRD pattern, consistent with single-phase Na_0.5K_0.5NbO₃, was obtained after calcination at 900°C for 6 h. Introducing 5 mol% excess Na₂CO₃ and K₂CO₃ into the starting mixture allowed milder calcination conditions to be used, for example 800°C for 2 h. Primary particles in 5 mol% excess samples were cuboid, with maximum sizes of ∼2.5 μm. Equiaxed 0.3–0.4-μm particles were formed for non-excess powders, and also for powders prepared with 1 and 3 mol% excess alkali carbonates. The results suggest liquid formation during calcination of the excess 5-mol% starting powders.