The effects of oxygen vacancies and their migrations on the dielectric responses of pure BaTiO3 (BT) ceramics and (Ba0.9Ca0.1)1.01(Ti0.9Zr0.1)O3 (BCTZ) ceramics, where portions of Ba and Ti were respectively substituted with Ca and Zr, were studied using wideband dielectric spectroscopy. The decrease in the dipole polarization of BT ceramics after annealing in a reducing atmosphere was due to domain-wall clamping by oxygen vacancies, while that of ionic polarization was attributable to lattice hardening by the incorporation of oxygen vacancies into the BT lattices. The dipole polarization of BCTZ ceramics indicated the same change as did that of BT ceramics after annealing, but the ionic polarization was independent of PO2 in annealing because of the anti-reducing behavior of BCTZ ceramics. The oxygen vacancy migration in BCTZ ceramics could be detected as a change of wideband dielectric spectra. The change observed only in the dipole polarization could be explained the oxygen vacancy migration from the anode to the cathode.
In this study, BaTiO3 powder was synthesized by using the co-precipitation of BaCl2 and TiOCl2 in a highly-alkaline solution at ambient pressure and a heating temperature lower than 100 • C. Control of both the pH of the sodium hydroxide (NaOH) solution and the concentrations of the starting raw materials was studied to evaluate their effects on the grain size and the homogeneity of the powder. Under the condition of a solution pH of 14 and a reaction temperature of 80 • C, an average particle size of 80 nm was estimated. X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy analyses showed that with high-energy ball milling in a bead mill, the uniformity and the dispersion of BaTiO3 particles could be enhanced.
Nonlinear dielectrics such as ferroelectrics, relaxors and frequency-tunable capacitors are desired to be handled in circuit simulators such as the SPICE. We have developed a software package to simulate a wide variety of nonlinear dielectrics in the SPICE. In the simulation of the polarization vs. electric field curve (P-E curve), the program code ''P-E simulator'' divided the P-E curve into two parts, a nonlinear dielectric part and a domain-switching part. In the former, the polarization was calculated as a linear expansion in terms of electric field, while in the latter, the polarization due to domain switching was calculated by assuming that the distribution of domain-switching probability was represented by Gaussian distribution functions. Two Gaussian distribution functions were required to accurately simulate the P-E curves of ferroelectric materials with the 180-degree and the non-180-degree domains. A circuit model with two capacitors and an arbitrary voltage source was proposed for a macromodel of nonlinear dielectrics in the SPICE. The netlist data to the SPICE were automatically generated using the program code ''Mk-netlist'' from the parameters determined using the P-E simulator. The P-E curves of a PZT thin film and multilayered ceramics capacitors were successfully simulated in the SPICE without the trial-and-error process.
A simple room temperature aerosol deposition (AD) process was used to fabricate silver thick films for high efficiency metallization that can be applied to decrease the resistance–capacitance delay and increase the signal propagation speed in integrated circuits. To obtain more advanced performance than aerosol-deposited silver films reported in previous studies, experimental parameters (orifice size of nozzle and gas consumption) that could directly affect electrical resistivity were optimized in advance. The proper small orifice size was selected for facilitated reduction of electrical resistivity by activating the percolation effect and making more conduction channels. High gas consumption also reduced the electrical resistivity of the silver films, forming plenty of metal clusters. Using experimental parameters that showed the lowest resistivity, silver thick films were fabricated via the AD process and their properties were analyzed. The results of the X-ray diffraction confirmed that the silver particles underwent impact-induced plastic deformation. As the film thickness was thickened up to 12 scans, the collided particles filled up the rough alumina substrate. After 12 scans, the silver films became densified due to severe plastic deformation of the as-deposited silver particles. Therefore, the growth mechanism suggests that most silver particles in the initial deposition step contribute to mechanical interlocking, and the subsequent particles could lead to film densification.
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