304 | wileyonlinelibrary.com/journal/jace J Am Ceram Soc. 2020;103:304–314. © 2019 The American Ceramic Society 1 | INTRODUCTION BaTiO 3 (BT) based dielectric ceramics have been exten- sively applied in electronic and electrical industries such as multilayer ceramic capacitors (MLCC), 1,2 random access memory, 3 and actuators 4 owing to their excellent dielectric properties. To meet the application requirements of working in harsh environments, 5 intense efforts have been devoted to maintain their high dielectric constant over a wide range of temperatures. 6,7 For example, forming solid solutions 8 and constructing core‐shell structures 9 by doping with various additives are thought to be effective approaches to enhance the dielectric temperature stability of BT‐based ceramics. The core‐shell structure is a chemically heterogeneous struc- ture within ceramics, which consists of three parts: pure BT grain core, paraelectric shell containing dopant elements and local gradients. It is generally thought that the combination of compositional gradient regions with various Curie tempera- tures results in a rather diffused and flat ε r ‐T curve. 10 Despite the fact that the core‐shell structure formation mechanism remains uncertain, general consensus has been reached that a limited diffusion process of dopants into BT Received: 25 May 2019 | Revised: 3 August 2019 | Accepted: 6 August 2019 DOI: 10.1111/jace.16735 ORIGINAL ARTICLE The role of diffusion behavior on the formation and evolution of the core‐shell structure in BaTiO 3 ‐based ceramics Cheng Chen 1 | Hua Hao 1 | Jingjing Cui 2 | Cong Yu 2 | Yingfei Tang 2 | Minghe Cao 2 | Zhonghua Yao 1 | Baoquan Wan 3 | Hanxing Liu 2 1 State Key Laboratory of Silicate Materials for Architectures, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, China 2 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, International School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, China 3 State Key Laboratory of Power Grid Environmental Protection, China Electric Power Research Institute, Wuhan, China Correspondence Hua Hao, State Key Laboratory of Silicate Materials for Architectures, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan, Hubei, China. Email: haohua@whut.edu.cn Funding information Natural Science Foundation of China, Grant/Award Number: U1601209, 51790490 and 51872213; National Key Basic Research Program of China (973 Program), Grant/Award Number: 2015CB654601; State Key Laboratory of Power Grid Environmental Protection, Grant/Award Number: GYW51201801173 Abstract In this work, the influence of starting particle size and sintering conditions on the microstructures and dielectric properties of BaTiO 3 ‐based ceramics coated with 0.3Bi(Zn 1/2 Ti 1/2 )O 3 ‐0.7BaTiO 3 were investigated to reveal the core‐shell structure by using high resolution transmission electron microscopy technique coupled with energy‐dispersive spectrometer analysis. The ion‐diffusion behavior plays a critical role in the formation and evolution of the core‐shell structure and, therefore, signifi- cantly influences the dielectric properties. When using starting powders containing BaTiO 3 particles larger than 100 nm in size and sintering for shorter dwelling times (0.5‐2.0 hours), a core‐shell structure could be formed and retained owing to the lim- ited diffusion behavior, enabling BaTiO 3 ‐based ceramics to meet the X8R specifica- tion for multilayer ceramic capacitors applications at high temperatures. However, when using 80 nm BaTiO 3 nanopowders and further extending the dwelling time to 6.0 hours, more driving energy was provided to prompt ion diffusion, which led to the compositional inhomogeneity becoming homogenized. KEYWORDS BaTiO 3 , core‐shell structure, dielectric properties, diffusion behavior