Giant dielectric properties of Na1/2La1/2Cu3Ti4O12 perovskite ceramic: First-principles and experimental investigations

Na1/2La1/2Cu3Ti4O12 ceramics were successfully fabricated via a sol-gel method. We found that the crystal structure of these sintered ceramics is identical to that of CaCu3Ti4O12, ICSD number 01-075-2188. A small quantity of CuO was observed due to the substitution of Na + at Cu2+ sites of the CaCu3Ti4O12 structure. Additionally, a small number of related Cu phases were discovered at grain junctions in these ceramics. Our Ab initio Molecular Dynamic simulations clearly revealed that oxygen vacancies are created during the sintering process. Additionally, at room temperature, our simulations showed that sites of the oxygen vacancies in the Na1/ 2La1/2Cu3Ti4O12 lattice are occupied by free oxygen, resulting in a lower oxygen vacancy density. Sintered Na1/ 2La1/2Cu3Ti4O12 ceramics present excellent dielectric properties, a high dielectric permittivity of 7780-9000 and a rather low dielectric loss tangent (0.041-0.042). From our electron density analysis, it was clearly seen that Cu+ and Ti3+ observed by the XPS measurements originated from the presence of oxygen vacancies in the Na1/ 2La1/2Cu3Ti4O12 structure. Electrical, DFT, and XPS studies indicated that the internal barrier layer capacitor (IBLC) model is the most appropriate for the colossal dielectric response in these ceramics.