Takehiro Konoike

BATIO3-BASED NON-REDUCIBLE LOW-LOSS DIELECTRIC CERAMICS

Dielectrics composed of BaTiO3-rare earth oxide-MgO have been studied to design a non-reducible low-loss dielectric material. Curie temperatures of dielectrics composed of BaTiO3–Gd2O3–MgO were lowered by Gd2O3, which provided the dielectrics with low power loss. It was found that the addition of BaZrO3 to BaTiO3–Gd2O3–MgO decreased the capacitance change with temperature. Gd2O3 diffused easily into BaTiO3, but, it could not easily diffuse into BaTiO3 to which BaZrO3 had been added. It was considered that BaZrO3 prevented the Gd2O3 diffusion into BaTiO3, resulting the remains of ferroelectricity and reduced capacitance change. Thus non-reducible and low power loss X7R dielectric ceramics were developed.

Piezoelectric Properties of Sn-Doped (K,Na)NbO3 Ceramics

It was previously reported that Ca-doped (K,Na)NbO3 + ZrO2 could be cofired with nickel inner electrodes in a reducing atmosphere. In the present study, the piezoelectric properties of Sn-doped (K,Na)NbO3 + ZrO2 ceramics were investigated. We prepared Sn-doped (K,Na)NbO3 + ZrO2 ceramics and Ca-doped (K,Na)NbO3 + ZrO2 ceramics by doping with Sn2+ and Ca2+ under reducing calcination. The Curie temperature Tc of the Sn-doped (K,Na)NbO3 + ZrO2 was 300 °C, which was the same as that of the Ca-doped (K,Na)NbO3 + ZrO2. The tetragonal–orthorhombic phase transition temperature and piezoelectric constant d33 of the Ca-doped (K,Na)NbO3 + ZrO2 were 130 °C and 130 pC/N while those of the Sn-doped (K,Na)NbO3 + ZrO2 were 50 °C and 190 pC/N, respectively. These results suggest that the piezoelectric d constant of (K,Na)NbO3-based multilayer ceramics with nickel inner electrodes can be increased by doping with Sn2+ instead of Ca2+.

Effect of Microstructure on Reliability of Ca(TiZr)O3-Based Multilayer Ceramic Capacitors

We examined the reliability of Ca(TiZr)O3 (CTZ)-based Ni-electrode multilayer ceramic capacitors (MLCs) prepared by two different processes with particular interest in the microstructure. One process was to calcine the mixture of CaCO3 and TiO2 to prepare CaTiO3 (CT) powder and the mixture of CaCO3 and ZrO2 to prepare CaZrO3 (CZ) powder, and then mix these calcined powders and sinter them to synthesize the CTZ-based ceramics. The other was to calcine the mixture of CaCO3, TiO2 and ZrO2 powders together to prepare CTZ powder and then sinter them. These two processes of CTZ ceramic preparation resulted in a different crystallinity and distribution of the elements. We found that these factors influenced the reliability of CTZ-based MLCs.

Orientation-controlled BaTiO3 thin films fabricated by chemical solution deposition

We synthesized orientation-controlled (100), (110), and (111) BaTiO3 films by the chemical solution deposition method. The electric properties of the fabricated BaTiO3 thin films were evaluated, and dielectric constants of 2000 were found for the (110)-oriented and (111)-oriented BaTiO3 film, with temperature dependence stabilized from 20 °C to 150 °C.

Study of nickel inner electrode lead-free piezoelectric ceramics

A (K,Na)NbO3 (KNN)-based multilayer piezoelectric ceramic with nickel inner electrodes was successfully fabricated by co-firing in a reducing atmosphere. We studied the compositional modification of KNN in order to increase reducing resistance in the sintering process, and obtained a good composition by using a solid solution with CaZrO3. A multilayer ceramic specimen had a ratio between the strain and induced electric field S/E of 360 pm/V, which is close to the highest value of KNN-type non-textured ceramics ever reported. Nickel is a suitable electrode material for multilayer structures with thinner ceramic layers, because of a high electro-migration resistance and low material cost. Thus, nickel inner electrode multilayer ceramics with KNN are good candidates as lead-free materials to replace PZT for several piezoelectric applications.

Effect of Ferroelectric Domain on Fatigue Fracture Behavior in Piezoelectric Ceramics

Fatigue tests on lead zirconate titanate (PZT) were performed by using single-edge-V-notched specimens under cyclic mechanical loading with or without superposition of a DC electric field. Fatigue life was prolonged by applying a DC electric field to the PZT ceramics. To estimate the domain contribution, fatigue tests on barium strontium titanate (BST) ceramics in both ferroelectric and paraelectric phase were carried out. The fatigue life of the ferroelectric phase was much shorter than that of the paraelectric phase. Comparing the fatigue lives of two PZT ceramics with different values of coercive electric field (Ec) revealed that the fatigue life of the PZT with higher Ec is about one order of magnitude longer than that with lower Ec when the stress-intensity factor of fatigue test is low. It is therefore concluded that non-180°domain switching probably deteriorates the fatigue life of ferroelectric ceramics.