Cheng-Shong Hong

Piezoelectric and ferroelectric properties of CN-doped K0.5Na0.5NbO3 lead-free ceramics

In this paper, lead-free (Na0.5K0.5)NbO3 ceramics doped with 1 mol % CuNb2O6 ceramics have been prepared by the conventional mixed oxide method with sintering temperature at 1075 °C. Microstructural analyses of NKN–xCN ceramics have been carried out and compared using x-ray diffraction and scanning electron microscope. The dependence of doping amount of the CN-doped NKN ceramics on the piezoelectric and ferroelectric properties has been investigated. The results show that the CN-doped NKN specimens sintered at 1075 °C present excellent “hard” piezoelectric properties of kp=40%, kt=45%, k33=57%, and ferroelectric properties Ec=25.5 kV/cm and Pr=22.63 μC/cm2. The mechanical quality factor (Qm) of NKN ceramics with CN additive is extraordinarily high (1933).

Fabrication of high-power piezoelectric transformers using lead-free ceramics for application in electronic ballasts

CuO is doped into (Na0.5K0.5)NbO3 (NKN) ceramics to improve the piezoelectric properties and thus obtain a piezoelectric transformer (PT) with high output power. In X-ray diffraction patterns, the diffraction angles of the CuO-doped NKN ceramics shift to lower values because of an expansion of the lattice volume, thus inducing oxygen vacancies and enhancing the mechanical quality factor. A homogeneous microstructure is obtained when NKN is subjected to CuO doping, leading to improved electrical properties. PTs with different electrode areas are fabricated using the CuO-doped NKN ceramics. Considering the efficiency, voltage gain, and temperature rise of PTs at a load resistance of 1 kΩ, PTs with an electrode with an inner diameter of 15 mm are combined with the circuit design for driving a 13-W T5 fluorescent lamp. A temperature rise of 6°C and a total efficiency of 82.4% (PT and circuit) are obtained using the present PTs.

Effects of the sintering temperature on the diffused phase transition and the spin-glassy behavior in Pb0.95La0.05(Fe2/3W1/3)0.65Ti0.35O3 ceramics

In this paper, the effect of the sintering temperature on the low-field dielectric behavior of nonstoichiometric Pb0.95La0.05(Fe2/3W1/3)0.65Ti0.35O3 relaxor ferroelectrics is investigated. The x-ray patterns and the scanning electron microscope images are used to detect the pyrochlore phase and the perovskite structure. The electric properties of the resistivity, the space charge polarization, the temperature-dependent dielectric constant and dielectric loss are discussed. The diffused phase transition and the ordering state are fitted and discussed by using the empirical law and two ordering models. Furthermore, the glassy behavior is determined by using the Curie–Weiss law and the spin-glass model. According to the experimental data and fitting results, the dielectric picture is changed from the short range order relaxorlike behavior to the long range order normal ferroelectric state as increasing the sintering temperature and the glassy behavior is weakened at the lowest and highest sintering temperatu...

Effects of synthesized method on glassy behavior and freezing process of 0.75PFW–0.25PT ceramics

Two different methods, the conventional direct oxide synthesized method and the two-step indirect synthesized (IS) method, were employed to synthesize the 0.75Pb(Fe2/3W1/3)O3–0.25PbTiO3 ceramics. The low-field dielectric responses were investigated using the empirical law and the Curie–Weiss law. The temperature-dependent local ordering parameters were derived from the experimental results using the spin-glass model and the modified-Landau theory separately. According to the experimental data and the fitting results, it is concluded that the temperature-dependent local order parameters are changed from a short-range-ordered relaxor to a long-range-ordered ferroelectric state using the IS method. On the basis of the physical concepts of the spin-glass model, the modified-Landau theory and the ordering models, it is suggested that local polarizations are affected not only by degree of ordering but also by space charge polarization. In contrast, the glassy behavior of local polarization is affected only by d...

Diverse resistive switching behaviors of AlN thin films with different orientations

Aluminum nitride (AlN) thin films with different orientations (i.e., amorphous, (100)- and (002)-oriented) are deposited on Pt/Ti/SiO2/Si substrates via the radio-frequency (RF) sputtering method. Among the three films, the amorphous AlN film is found to provide both the lowest leakage current (2.6 × 10−11 A) and the largest memory window size (3.1 × 106). Moreover, the observation results suggest that the thermal activation energy has a greater effect on the conduction behavior of the Ag/AlN/Pt structures than the microstructure, surface morphology, or chemical bonds.