Solubility and diffusivity of Ho ions were evaluated in ceramics into which Ho ions were implanted using an accelerating voltage of 500keV. The depth profile of the ions was composed of 3 regions in post-annealed samples: 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 it was 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 suggested 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 5 orders of magnitude larger than the volume diffusion coefficients. The solubility of Ho ions was estimated to be a few thousand ppm in barium titanate ceramics.

Diffusion and Solubility of Holmium Ions in Barium Titanate Ceramics. J.Itoh, H.Haneda, S.Hishita, I.Sakaguchi, N.Ohashi, D.C.Park, I.Yashima: Journal of Materials Research, 2004, 19[12], 3512-20