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Microstructural,optical, and electrical characteristics of Ni/C doped BST thin films
Authors:Fahimeh Emadi  Ali Nemati  Manuel Hinterstein  Esmaeil Adabifiroozjaei
Affiliation:1. Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran;2. Institute for Applied Materials, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany;3. Research Center for Functional Materials (RCFM), National Institute for Materials Science (NIMS), Tsukuba 305-0047, Japan
Abstract:In the present work the effect of simultaneous doping of carbon and nickel on the microstructural, optical, and electrical properties of barium strontium titanate (BST) is investigated. Thin films of BST were prepared by the sol-gel method in six different compositions ((Ba0.6Sr0.4)(NixCyTi1-x-y)O3): x?=?y?=?0.00 (BST), x?=?0.04?y?=?0.00 (BST4N), x?=?0.04?y?=?0.01 (BST4N-1C), x?=?0.04?y?=?0.02 (BST4N-2C), x?=?0.04?y?=?0.03 (BST4N-3C), and x?=?y?=?0.04 (BST4N-4C). Structural features and chemical bonds of the films were studied by TGA/DSC, XRD, FT-IR, and FE-SEM. The electrical and optical properties of the films were analysed by impedance spectroscopy and UV–VIS spectroscopy. The results show that addition of Ni and C leads to Ti4+-Ni2+ and Ti4+-C4+ replacements, respectively. These replacements lead to a gradual increase in the band gap energy; from 3.15?eV for BST to 3.44, 3.5, 3.66, 3.73 and 3.76?eV for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. In contrast, the dielectric loss decreases significantly from 0.055 for BST to 0.031, 0.033, 0.03, 0.022 and 0.01 for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. At the same time, the quality factor Qf (1/ tanδ) increases substantially from 15 for BST to 32, 30, 33, 44 and 87 for BST4N, BST4N-1C, BST4N-2C, BST4N-3C, and BST4N-4C, respectively. In contrast, the frequency dependence of the capacity decreases in comparison to un-doped BST. Among all films, the BST4N-4C had the highest figure of merit (FOM), least dielectric loss, and very low frequency-dependence, making it the best candidate for tuneable device applications.
Keywords:Ion doping  Dielectric properties  Optical properties  Sol-gel  Thin-film
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