Effect of Oxygen Partial Pressure on the Dielectric Properties and Microstructures of Cofired Base‐Metal‐Electrode Multilayer Ceramic Capacitors

Abstract

The dielectric properties, dopant distributions, and microstructures of BaTiO 3 -based multilayer ceramic capacitors (MLCCs) sintered in H 2 -N 2 -H 2 O atmospheres with P O 2 5 10 À7.5 Pa (BMX-7.5) and P O2 5 10 À9.5 Pa (BMX-9.5) were studied, and the effects of oxygen partial pressures were analyzed. Dielectric measurements showed that BMX-7.5 had a lower dielectric constant at temperatures above 201C, but a higher dielectric constant at temperatures below 101C when compared with BMX-9.5. The coexistence of core-shell and core grains was observed in bright field (BF) transmission electron microscopy images in both types of capacitors. Triple-point and grain boundary phases were observed more frequently in BMX-9.5 than in BMX-7.5, and energy-dispersive X-ray spectrometer point-by-point analysis revealed that these second phases contained high concentrations of dopants such as Si, Y, and Ca. The dopant concentration in the shell regions in BMX-7.5 was higher than that in similar regions in BMX-9.5. Smeared and twisted grain boundaries with fringes observed in both types of MLCCs indicated that the shell regions in both samples were formed either by diffusion of foreign ions into BaTiO 3 or by crystallization of grain boundary and triple-point liquid phases. It was deduced that the partial pressure of oxygen in the sintering atmosphere influenced the microstructures, dopant distributions, and coreshell ratios of the grains in these materials. J ournal

Dielectric and piezoelectric properties of (Ba0.95Ca0.05)(Ti0.88Zr0.12)O3 ceramics sintered in a protective atmosphere

“…The two devices which benefit in particular are multilayer ceramic capacitors (MLCCs) 1 and multilayer ceramic actuators. 2 These devices, however, must be sintered in a reducing atmosphere to prevent oxidation of the electrodes.…”

Evaluation of dielectric and piezoelectric behavior of unpoled and poled barium titanate polycrystals with oxygen vacancies using phase field method

“…In the aforementioned two papers, it was shown that the permittivity and piezoelectric constant increase with decreasing average grain size and reach the maximum at about 1 μm. On the other hand, it has been shown that the electrical properties and microstructures of the BaTiO 3 ceramics depend on the oxygen partial pressure [8,9]. Although grain size and oxygen activity have been found to play a significant role in dielectric and piezoelectric behavior of BaTiO 3 ceramics, it is difficult to find the optimal conditions experimentally.…”

Sintering and electrical properties of Cu-particle-dispersed (Na,K,Li)NbO3

“…It is also reported that perovskite PZT films can be directly deposited onto base www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 36 (2010) 583-587 metal Cu foils [14,15] for microelectromechanical systems (MEMs) application. The processing atmosphere should be controlled in an appropriate oxygen partial pressure window in order to avoid oxidation of base metals [12][13][14][15]. In this study, we demonstrated that perovskite (Na,K)NbO 3 -based (NKN) piezoceramics can also be cofired with base metal Cu in a protective atmosphere.…”

“…Base metal electrode (BME) has become a hot issue for a long time [11]. The Ni electrode is commonly cofired with BaTiO 3 -based dielectrics to produce BME MLCCs [12,13]. It is also reported that perovskite PZT films can be directly deposited onto base www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 36 (2010) 583-587 metal Cu foils [14,15] for microelectromechanical systems (MEMs) application.…”