Noriyuki Kubodera

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+.

Potassium Sodium Niobate-Based Lead-Free Piezoelectric Multilayer Ceramics Co-Fired with Nickel Electrodes

Although lead-free piezoelectric ceramics have been extensively studied, many problems must still be overcome before they are suitable for practical use. One of the main problems is fabricating a multilayer structure, and one solution attracting growing interest is the use of lead-free multilayer piezoelectric ceramics. The paper reviews work that has been done by the authors on lead-free alkali niobate-based multilayer piezoelectric ceramics co-fired with nickel inner electrodes. Nickel inner electrodes have many advantages, such as high electromigration resistance, high interfacial strength with ceramics, and greater cost effectiveness than silver palladium inner electrodes. However, widely used lead zirconate titanate-based ceramics cannot be co-fired with nickel inner electrodes, and silver palladium inner electrodes are usually used for lead zirconate titanate-based piezoelectric ceramics. A possible alternative is lead-free ceramics co-fired with nickel inner electrodes. We have thus been developing lead-free alkali niobate-based multilayer ceramics co-fired with nickel inner electrodes. The normalized electric-field-induced thickness strain (Smax/Emax) of a representative alkali niobate-based multilayer ceramic structure with nickel inner electrodes was 360 pm/V, where Smax denotes the maximum strain and Emax denotes the maximum electric field. This value is about half that for the lead zirconate titanate-based ceramics that are widely used. However, a comparable value can be obtained by stacking more ceramic layers with smaller thicknesses. In the paper, the compositional design and process used to co-fire lead-free ceramics with nickel inner electrodes are introduced, and their piezoelectric properties and reliabilities are shown. Recent advances are introduced, and future development is discussed.

Improvement of the Reliability of Dielectrics for MLCC

To achieve enough reliability of monolithic ceramic capacitor, it is important to know the contribution of grain boundary and grain interior to its reliability and insulation resistance. As the number of grain boundaries per layer increased, mean time to failure (MTTF) increased. In addition, as the number of grain boundaries per layer increased, samples showed lower current leakage in the measured electric field range. Using these data, the grain boundary E-J curves were determined by simulation. As a result, temperature and electric field dependence of insulation resistance of grain boundary were very low. The insulation characteristics of one BaTiO3 grain per layer were examined. The resistance and reliability of grain interior were very low. To improve the degradation resistance of grain interior, Ca-doped BaTiO3-based dielectrics were developed. The influence of Ca substitution on MTTF was investigated and it was found out that MTTF increased with the increase of Ca substitution.

Processing and enhanced piezoelectric properties of highly oriented compositionally modified Pb(Zr,Ti)O3 ceramics fabricated by magnetic alignment

Highly oriented compositionally modified Pb(Zr,Ti)O3 (PZT) ceramics were successfully obtained by slip casting in a high magnetic field. PZT is a well-known superior ceramic with the highest piezoelectric properties, and these properties have been expected to be further improved through crystalline orientation. However, highly oriented PZT ceramics fabricated by slip casting in a high magnetic field have never been reported. We obtained oriented ceramics using compositionally modified PZT with Pb(Ni,Nb)O3, and their Lotgering factor was 0.77. The electromechanical coupling coefficient (k31) increased by 30%, and an extremely high value of 0.44 was achieved for the oriented ceramics.