Controlling dielectric properties of Nb + X (X = Al, Ga, In) co-doped and Nb-doped rutile-type TiO2 single crystals. Issue 4 (3rd January 2023)

• Record Type: Journal Article
• Authors: Kakimoto, Shota; Hashimoto, Yujiro; Kuwano, Taro; Kimura, Koji; Hayashi, Kouichi; Hagiwara, Manabu; Deguchi, Kazuhiko; Taniguchi, Hiroki
• Is Part Of: Journal of materials chemistry. Volume 11:Issue 4(2022)
• Page Start: 1304
• Page End: 1310
• Publication Date: 2023-01-03
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d2tc03914a
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Dielectric properties of Nb-doped TiO2 single crystals measured before and after the special post-annealing with Ga2 O3 embedding powder, shedding light on local structure engineering for permittivity boosting in dielectric materials. Abstract : Co-doping of heterovalent ions to rutile-type TiO2 has recently attracted attention as a new concept for designing high-permittivity materials with local structure engineering. However, the role of co-dopants in permittivity enhancement remains an open question. In the present study, dielectric measurements are performed in Nb + X (X = Al, Ga, In) co-doped and Nb-doped rutile-type TiO2 single crystals before and after annealing in X2 O3 powders. The apparently huge permittivity, on the order of 10 5, is observed in all as-grown samples. Systematic analyses of dielectric relaxation observed in the as-grown samples clarify that thermally excited carriers render the sample semiconducting, thus giving rise to the apparently huge permittivity. In the post-annealed samples, in contrast, the huge permittivity disappears, and the dielectric loss markedly decreases to indicate recovery of the insulating property. X-ray fluorescence analyses show that the insulation recovery stems from migration of X cations into the single crystal, which is caused by the post-annealing. The post-annealing time dependence of the dielectric properties indicates that minute control of the Nb-to-X ratio is crucial for simultaneously achieving both the large permittivity and the fine insulating property in the co-doped TiO2 . The present results offer an important clue toward clarifying the mechanism of permittivity boosting in co-doped TiO2 .