Shigeki Sato

Mechanism of improvement of resistance degradation in Y-doped BaTiO3 based MLCCs with Ni electrodes under highly accelerated life testing

Abstract The mechanism of improvement of resistance degradation in Y-doped BaTiO3 based multilayer ceramic capacitors (MLCCs) with Ni electrodes has been studied using electrical measurement techniques, minor phase identification and the measurement of oxygen vacancy concentration. Admittance spectroscopy and thermally stimulated current measurements show the relaxation due to barium vacancy states caused by Y doping. The minor phase identification by XRD indicated those Y3+ substitutes for perovskite A-site. Oxygen vacancy concentration measurement indicated that Y decreases the oxygen ion vacancy concentration in BaTiO3. These results suggest that Y3+ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance degradation.

Effect of Y-Doping on Resistance Degradation of Multilayer Ceramic Capacitors with Ni Electrodes under the Highly Accelerated Life Test

The effect of Y-doping on the degradation behavior of insulation resistance for multilayer ceramic capacitors with Ni electrodes has been studied using electrical measurement techniques such as admittance spectroscopy, thermally stimulated current (TSC), and electrical conductivity measurements. TSC measurements show that a strong internal bias field remained after applying an electrical field at a high temperature, like during highly accelerated life testing. This internal bias field originated from the migration of positive carriers. Admittance spectroscopy indicated three types of relaxation, with activation energies of 0.4, 0.8, and 0.8–1.0 eV. The intensity of the 0.4 eV relaxation peak increased with Y3+ doping and disappeared at low oxygen partial pressure ( PO2) annealing. The existence of holes was also observed from the temperature dependence of insulation resistance. The 0.4 eV relaxation is considered to be due to the transition of electrons from the valence band to barium vacancy states. These results suggest that Y3+ acts as a donor and creates barium vacancies, which compensate for the oxygen vacancies and thereby improve the resistance to degradation.

Fabrication and Electrical Properties of Mn-Doped KNbO3 Ceramics Synthesized from KHCO3 as a Starting Material

Potassium niobate-based ceramics with 0.1 wt % MnCO3, K(1+x)NbO3+MnCO3 0.1 wt % (KN10000x+Mn, x = 0.0000–0.0010), were fabricated using KHCO3 powder as a starting material. The KN10000x+Mn ceramics were basically fabricated using a conventional ceramic fabrication process and MnCO3 powders were added at the milling stage after the calcination. High density ratios above 95% were prepared for the wide compositional range of excess K amount for KN10000x+Mn ceramics. From these results, Mn ions are thought to act as a sintering aid for KN ceramics. Mn-doped KN10000x ceramics also showed high resisitivities of approximately 1012 Ω cm for the wide variety of x (10000x=0–9). Moreover, the electromechanical coupling factors k33 for KN10000x+Mn had constant values of higher than 0.50.

Synthesis and Characterization of Barium Titanate Nano-Powders by the Hydrothermal Process

Barium titanate (BaTiO3) nano-particles with high crystalinity were synthesized by hydrothermal process using Ba(OH)2·8H2O and TiO2 as source materials. The average size of the synthesized BaTiO3 particles decreased as the TiO2 particle size decreased. The amount of hydroxide ions incorporated into the perovskite lattice decreased as the BaTiO3 particle size increased and then became constant above 50 nm. Moreover, the ratio of the c- to a-axis length increased when the BaTiO3 particle size was above 50 nm. Sintered ceramics with a grain size smaller than 100 nm were obtained by using highly crystallized hydrothermal BaTiO3 particles.

High-Power Piezoelectric Characteristics of Sr2Bi4Ti5O18-Ca2Bi4Ti5O18-Based Ferroelectric Ceramics

The high-power piezoelectric characteristics of lead-free piezoelectric ceramics, based on a bismuth layer-structured ferroelectric, MnCO3-doped (Sr0.7Ca0.3)2Bi4Ti5O18 (abbreviated as SCBT0.3 + Mn x wt%), were studied. SCBT0.3 + Mn x wt% lead-free ceramics showed an extremely high mechanical quality factor (Qm) of more than 3000 in the (33) vibration mode under small-amplitude vibration. The high-power piezoelectric characteristics of SCBT0.3 + Mn x wt% were measured using the high-power measurement method based on frequency sweep driving under a constant voltage condition. It was found that the vibration velocity v0-p of SCBT0.3 + Mn 0.2 wt% linearly increased up to approximately 3.0 m/s. Therefore, the Mn-doped SCBT0.3-based ceramics are a promising candidate for lead-free high-power applications.

Powder and Dielectric Characterization of Hydrothermally Synthesized Barium Titanate Nanopowders

Barium titanate (BaTiO3) particles with average size of smaller than 100 nm were synthesized by a hydrothermal process at 100°C to 300°C. The c- to a-axis ratios of the particles increased as the synthesis temperature increased. Disk capacitors were fabricated with as-synthesized particles and some additives to obtain X7R capacitors. The temperature coefficient of capacitance with particles synthesized at 100°C was much larger than that for 300°C, indicating that the former had uniform composition in the grain while the latter had a core-shell structure. This data show that barium titanate particles hydrothermally synthesized at high temperature are useful when creating the X7R capacitors with small grain size.

Fabrication and Reproducibility of Dense KNbO3 Ceramics Synthesized from KHCO3 as a Starting Material

Dense potassium niobate ceramics, K(1+x)NbO3 (KN-10000x, x = 0–0.001), were fabricated using KHCO3 powder as a starting material to improve their reproducibility, and the densification flow were also discussed in this paper. The KN-7.2 ceramics all had high density ratios exceeding 96% and resistivities of above 1012 Ω˙cm. The relative density ratios of all the KN-7.2 ceramics were similar, showing the excellent reproducibility obtained using KHCO3 powder as a starting material. The electromechanical coupling factor k15 and piezoelectric strain constant d15 of the KN-7.2 ceramics were 0.46 and 153 pC/N, respectively.