Comparative dielectric studies of nanostructured BaTiO 3 , CaCu 3 Ti 4 O 12 and 0.5BaTiO 3 ⋅ 0.5CaCu 3 Ti 4 O 12 nano-composites synthesized by modified sol–gel and solid state methods Laxman Singh a , Uma Shanker Rai b , Kam Deo Mandal c , Byung Cheol Sin a , Hyung-il Lee a , Hoeil Chung d , Youngil Lee a, ⁎ a Department of Chemistry, University of Ulsan, 93 Daehak-ro Nam-gu, Ulsan 680-749, Republic of Korea b Department of Chemistry, Centre of Advanced Study, Faculty of Science, Banaras Hindu University, Varanasi 221005, U.P., India c Department of Chemistry, Indian Institute of Technology, Banaras Hindu University, Varanasi 221005, U.P., India d Department of Chemistry, Hanyang University, Haengdang-dong 17, Seongdong-Gu, Seoul 133-791, Republic of Korea abstract article info Article history: Received 12 February 2014 Received in revised form 15 July 2014 Accepted 17 July 2014 Available online 18 July 2014 Keywords: Nano-structure Electron microscopy Semi-wet gel route Dielectric properties BaTiO 3 (BTO), CaCu 3 Ti 4 O 12 (CCTO) and 0.5BaTiO 3 ·0.5CaCu 3 Ti 4 O 12 (BTO–CCTO), as a new nano-composite ceram- ic, were successfully designed and fabricated by a semi-wet gel route and a modified solid state method. The di- electric properties of the BTO–CCTO ceramic were compared to those of the BTO and CCTO ceramics at lower sintering temperatures and durations. The X-ray diffraction analysis revealed that the BTO and CCTO ceramics form a single crystalline phase and the average crystalline sizes calculated from X-ray diffraction data were in the range of 40–65 nm. The particle sizes of the BTO, CCTO, and BTO–CCTO ceramics obtained from transmission electron microscopy images were in the ranges of 40–65 nm, 80–110 nm, and 70–95 nm, respectively. The phase composition and microstructure were studied by X-ray diffraction and scanning electron microscopy. The energy dispersive X-ray results demonstrated the purity and stoichiometry of the BTO–CCTO nano-composite. The grain sizes of the BTO, CCTO and BTO–CCTO ceramics were found to be in the ranges of 500 nm–1 μm, 4–24 μm, and 250 nm–4 μm, respectively. The AC conductivity as a function of frequency confirmed the semiconducting nature of all of the ceramics and obeyed the Jonscher's power law. The impedance spectrum measurement result showed that the CCTO ceramic possessed an exceptional grain boundary resistance, which supports the internal barrier layer capacitance (IBLC) mechanism present in this ceramic and is responsible for the high ε r values. © 2014 Elsevier Inc. All rights reserved. 1. Introduction Materials possessing a large dielectric constant have gained a great deal of attention. Since the discovery of ferro-electricity in a single crys- tal of Rochelle salt in 1921 [1], there have been many attempts to find new materials which possess a high dielectric constant (ε r ). The urgent demand for ceramic capacitors with high dielectric constants has been a key issue leading to the development of ceramic capacitor technology. High dielectric constant materials are desirable for the miniaturization of capacitors required for integrated circuits in electronic devices. BaTiO 3 and SrTiO 3 -based ferroelectric materials exhibit high dielectric constants, but the dielectric constants of these materials show strong temperature dependencies, which are not desirable from the device point of view [2,3]. Recently, we utilized BaTiO 3 or relaxor ferro- electrics such as Pb(Mg 1/3 Nb 2/3 )O 3 [PMN], Pb(Zn 1/3 Nb 2/3 )O 3 [PZN] and Pb 1 - x La x (Zr 1 - y Ti y )O 3 [PLZT] [4], which are not environmentally friendly as capacitor materials (dielectric constant = 1000–20,000). BaTiO 3 is a ferroelectric perovskite which is quite unstable and shows phase transition. High-K ferroelectric materials exhibiting phase transi- tion near the Curie temperature are not the best choices. On the other hand, CaCu 3 Ti 4 O 12 (CCTO) ceramic has a high dielectric constant (ε r ≈ 10 4 –10 5 ) independent of frequency (10 2 –10 6 Hz) and tempera- ture (100–600 K) [5,6], which makes it a promising material for applica- tion in microelectronics and memory devices as a static dielectric material suitable for miniaturization. It may be widely used in electronic industries to manufacture electronic components such as multilayer ca- pacitors (MLCCs), dynamic random access memory (DRAM), micro- wave devices, and electronic devices in automobiles and aircrafts [7–10]. Unfortunately, CCTO ceramic with its large dielectric constant ex- hibits high dielectric loss that limits its practical applications in elec- tronic industries. Based on this, scientists and technologists are intensively developing thermally stable high ε r material alternatives which have a constant value over a wide frequency region. Up to now, although several investigations have been conducted on the di- electric properties of CCTO ceramics and their single crystal as well as related materials, the high loss tangent (tan δ) of CCTO ceramics Materials Characterization 96 (2014) 54–62 ⁎ Corresponding author. E-mail address: nmryil@ulsan.ac.kr (Y. Lee). http://dx.doi.org/10.1016/j.matchar.2014.07.019 1044-5803/© 2014 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect Materials Characterization journal homepage: www.elsevier.com/locate/matchar