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

Abstract

In this work, Y2/3Cu3Ti4O12 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 Y2/3Cu3Ti4O12 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 Y2/3Cu3Ti4O12 samples. Density functional theory (DFT) calculations were used to investigate the most stable structure of the Y2/3Cu3Ti4O12 ceramics. Our DFT results reveal that two calcium vacancies (VCa) are isolated from each other. We also determined the lowest energy configuration of an oxygen vacancy (VO) in the Y2/3Cu3Ti4O12 ceramics occurred during the sintering process. We found that the VO 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 Y2/3Cu3Ti4O12 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 Y2/3Cu3Ti4O12 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 Y2/3Cu3Ti4O12 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 VO. Consequently, high dielectric permittivity in Y2/3Cu3Ti4O12 may have originated from an internal barrier layer capacitor (IBLC) effect.