Diffusion and solubility of holmium ions in barium titanate ceramics
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Hajime Hanedaa) National Institute for Materials Science/Advanced Materials Laboratory, Tsukuba, Ibaraki 305-0044, Japan; and Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Fukuoka 816-8560, Japan
Shunichi Hishita, Isao Sakaguchi, Naoki Ohashi, and Dae-Chul Park National Institute for Materials Science/Advanced Materials Laboratory, Tsukuba, Ibaraki 305-0044, Japan
Isamu Yashima Mitsui Mining & Smelting Co. Ltd., Corp. R&D Center, Saitama 362-0021, Japan (Received 19 March 2004; accepted 6 August 2004)
Ho ion solubility and diffusivity were evaluated in barium titanate ceramics in which Ho ions were implanted with an accelerating voltage of 500 keV. The depth profile of the ions was composed of three regions in the post-annealed sample: the first was the precipitation region, the second was a region created by lattice diffusion of Ho ions, and the third was a region created by grain-boundary diffusion. The Ho lattice diffusion characteristics were similar to those of Ni ion diffusion in barium titanate ceramics, and we concluded that the diffusion mechanism was the same as that responsible for Ni ions. The Ho ions diffused through the B-site (Ti-site) and were then exchanged with A-site ions. This mechanism suggests that a small number of Ho ions dissolved in the B-site. Preferential grain-boundary diffusion was also observed. The grain-boundary diffusion coefficients were four to five orders of magnitude larger than the volume diffusion coefficients. The solubility of Ho ions was estimated to be a few thousand parts per million in barium titanate ceramics. I. INTRODUCTION
Mobile electronic devices such as cellular phones and personal computers have become smaller and lighter, with better performance, and lower power consumption. The integration and miniaturization of passive components, such as capacitors, inductors, and resistors, have also been accelerating. Multilayer ceramics capacitors (MLCCs) are particularly important electronic components that are used in almost all areas of electronics.1 Traditionally, MLCCs have been made of internal electrode layers of precious metals and barium titanate dielectrics (BTO). It is obvious that replacing the precious metal electrodes with base metal electrodes (BMEs) would significantly reduce production costs.2 Saito et al. found the best candidate for such replacement to be Ni.3
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0466 3512
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 12, Dec 2004 Downloaded: 23 Feb 2015
Using Ni for the internal electrodes had been found to pose problems such as ion migration, which occurred at the metal (electrode)–dielectric interface, and the establishment of techniques to control the interface properties has become a matter of some urgency. In response to this, we have already reported on the diffusivity of Ni (internal electrode material) into dielectrics.4 Our results indicated that dielectrics of submicron thickness could be used
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