Dielectric Properties and Nonlinear Electrical Response of Nb⁵⁺/Cr³⁺-Codoped CaCu₃Ti₄O₁₂ Ceramics

Adding Nb5+/Cr3+ codopants to CaCu3Ti4O12 ceramics via a solid-state reaction can significantly reduce the low-frequency loss tangent (tan delta approximate to 0.043) compared to undoped and single-doped (either with Nb5+ or Cr3+) CaCu3Ti4O12 ceramics. Interestingly, very high dielectric permittivities of 99,098 are obtained together with excellent dielectric-frequency stability. In comparison to single-doped ceramics, the grain boundary resistance (R-gb similar to 5.0 x 10(6) Omegacm) at room temperature has increased significantly. Based on density functional theory calculations, the Cr3+ ion tends to remain distant from the Nb5+ ion in this lattice. Furthermore, it was found that Cr3+ can induce oxygen vacancies in the Nb5+/Cr3+-codoped CaCu3Ti4O12 structure, resulting in an increase in the oxygen vacancy concentration within the grains of the samples containing Cr ions. Both experimental and computational results support the internal barrier layer capacitor model. This model highlights the grain boundary properties responsible for controlling the giant dielectric properties of the Nb5+/Cr3+-codoped CaCu3Ti4O12 ceramics.