High dielectric permittivity and dielectric relaxation behavior in a Y2/3Cu3Ti4O12 ceramic prepared by a modified Sol?Gel route

In this work, Y_2/3Cu₃Ti₄O₁₂ ceramics were fabricated via a modified sol?gel route. Structural, dielectric, and electrical parameters were systematically investigated. The XRD results indicate that a CaCu₃Ti₄O₁₂ phase (JCPDS No. 75–2188) is present in every sintered sample. SEM images of Y_2/3Cu₃Ti₄O₁₂ ceramics disclose a fine-grained ceramic microstructure. Interestingly, high dielectric permittivity, ～6600–7600, with loss tangents of ～0.918–1.086 were achieved in the sintered Y_2/3Cu₃Ti₄O₁₂ samples. Density functional theory (DFT) calculations were used to investigate the most stable structure of the Y_2/3Cu₃Ti₄O₁₂ ceramics. Our DFT results reveal that two calcium vacancies (V_Ca) are isolated from each other. We also determined the lowest energy configuration of an oxygen vacancy (V_O) in the Y_2/3Cu₃Ti₄O₁₂ ceramics occurred during the sintering process. We found that the V_O is trapped close to the Y atom in this structure. Both computational and experimental studies specify that the oxygen vacancy is located close to the Y atom in the Y_2/3Cu₃Ti₄O₁₂ lattice and it might be a bivalent oxygen vacancy. As a result, due to charge balance, charge compensation of the transition ions, i.e., Cu and Ti ions, might take place. The charge compensation mechanisms in the Y_2/3Cu₃Ti₄O₁₂ lattice were verified using an XPS technique. Impedance spectroscopy confirms the presence of an inhomogeneous microstructure consisting of semiconducting grains and insulating grain boundaries in the sintered Y_2/3Cu₃Ti₄O₁₂ ceramics. This electrical result is consistent with the computational analysis, showing that a charge compensation mechanism might be involved in generation of the grains' semiconductive region due to the presence of a V_O. Consequently, high dielectric permittivity in Y_2/3Cu₃Ti₄O₁₂ may have originated from an internal barrier layer capacitor (IBLC) effect.