Comparative dielectric studies of nanostructured BaTiO3, CaCu3Ti4O12 and 0.5BaTiO3? 0.5CaCu3Ti4O12 nano-composites synthesized by modified sol–gel and solid state methods

BaTiO₃ (BTO), CaCu₃Ti₄O₁₂ (CCTO) and 0.5BaTiO₃·0.5CaCu₃Ti₄O₁₂ (BTO–CCTO), as a new nano-composite ceramic, were successfully designed and fabricated by a semi-wet gel route and a modified solid state method. The dielectric 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.