The optical, dielectric and non-Ohmic properties of La-modified CdCu3Ti4O12 thin films

Two-dimensional (2D) materials with dual-functional dielectric and varistor properties, such as CdCu 3 Ti 4 O 12 (CdCTO) films, have great application potential in multi-functional integration of electronics and energy systems. However, reducing the dielectric loss tangent (tanδ) and increasing the breakdown field strength ( E b ) of CdCTO films, while maintaining their high dielectric constant (ε′) is still a challenge. In this work, La 3+ doping via a sol-gel method was implemented to modify the optical, dielectric and non-Ohmic properties of CdCu 3 Ti 4 O 12 thin films. The La-doped thin films exhibited a single-phase structure and suppressed the grain growth at varying optical band gaps from 3.61 to 3.21 eV. The grain boundary (GB) resistance and the barrier height were increased significantly in the doped films, thereby exerting positive effects on tanδ, E b and nonlinear coefficient (α). The ε′ parameter followed the internal barrier layer capacitor (IBLC) model, decreasing with the grain size, but remained at a relatively high value. As a result, an extremely low tanδ of ∼ 0.011 and high E b of ∼ 82.1 kV/mm along with ε′ of ∼ 8890 and α of ∼ 6.64 were obtained in Cd 0.91 La 0.06 Cu 3 Ti 4 O 12 film. The relaxation mechanism in the medium frequency range was ascribed to a Maxwell–Wagner relaxation related to GBs. Therefore, effective methods were proposed to obtain double-functional films that possess excellent dielectric and non-Ohmic properties simultaneously.