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https://doi.org/10.1007/s11664-020-08515-x  2020 The Minerals, Metals & Materials Society

Effects of Y Doping on Dielectric and Varistor Properties of CaCu3Ti4O12 Thin Films HUA MAN,1,2 WENWEN YE,2 LIANG ZHANG,2 YUJUN DENG,2 SUJUAN ZHONG,3 SANMING DU,4 and DONG XU 1,2,5 1.—College of Material Science and Engineering, East China Jiaotong University, Nanchang 330013, China. 2.—Key Laboratory of Metallurgical Emission Reduction and Resources Recycling (Anhui University of Technology), Ministry of Education, Ma’anshan 243002, China. 3.—Zhengzhou Research Institute of Mechanical Engineering, Zhengzhou 450001, China. 4.—School of Materials Science and Engineering, Henan University of Science and Technology, Luoyang 471000, China. 5.—e-mail: [email protected]

Ca13x/2YxCu3Ti4O12 (x = 0, 0.05, 0.1, 0.15, and 0.2) (CCTO) thin films were prepared by a modified sol–gel method. The effects of Y doping on the microstructure and electrical properties of the CCTO thin films were investigated. According to x-ray diffraction analysis, the main phase of all Y-doped  Meanwhile, some secondary phases were deCCTO thin films is cubic Im3. fected. Scanning electron microscopy analysis showed that Y doping can easily lead to a smaller grain size and larger porosity in CCTO thin films. Roomtemperature dielectric analysis showed that the dielectric constant of different Y doping samples at 1 kHz was 4213, 4523, 4974, 4824, and 4777, and the dielectric losses were 0.053, 0.051, 0.062, 0.067, and 0.049, respectively. The study of Y-doped CCTO thin films showed that Y doping increased the dielectric constant of the films at low frequencies, but at the same time it increased their dielectric loss and decreased their dielectric frequency and temperature stability range. Y-doping had little effect on the nonlinearity of the films and did not significantly change their nonlinear coefficients. Key words: Sol–gel method, doping, CaCu3Ti4O12, dielectric properties, nonlinear coefficient

INTRODUCTION In 2000, Subramanian et al.1,2 first reported CaCu3Ti4O12 (CCTO) with a large dielectric constant, of 12,000 at 1 kHz. The dielectric constant was almost constant over a wide temperature range (100–400 K), and no phase change occurred in this range. In addition, in 2004, Chung et al.3 found that polycrystalline CCTO ceramics have good varistor characteristics, and the nonlinear coefficient a of a sample measured in the range of 5–100 mA was as high as 912, which is much larger than that of a conventional ZnO varistor.4,5 In recent years, these excellent electrical properties have made CCTO of

(Received December 11, 2019; accepted September 22, 2020)

more interest for researchers in the field of electronic ceramics.6–10 However, the dielectric loss of CCTO ceramics is very high,11,12 which is still a problem that cannot be ignored in practical applications. Many researchers have proposed various methods to reduce the tand of CCTO. For example, adding a secondary phase,13,14 replacing a suitable metal ion,11,15 reducing the grain size,16,17 increasing