Dielectric characteristics of a (Cd2+, F-) co-doped CaCu3Ti4O12/CaTiO3 binary system improved with increased dielectric permittivity and decreased dielectric loss tangent

Abstract

Improved dielectric properties can be achieved in a binary-phase system of CaCu3Ti4O12/CaTiO3 by doping it with CdF2 to produce Ca2-xCdxCu2Ti4O12-2yF2y (x = y = 0, 0.05, 0.10, and 0.15). These ceramics were fabricated using a solid-state reaction method. A composite phase between CaCu3Ti4O12/CaTiO3 at a ratio ∼ 66.7/33.3 mol% was found in Ca2-xCdxCu2Ti4O12-2yF2y samples. The grain size of Ca2-xCdxCu2Ti4O12-2yF2y decreases with increasing dopant concentration. Interestingly, the dielectric permittivity of Ca2-xCdxCu2Ti4O12-2yF2y ceramics is more than doubled from 3446 → 7461 by increasing CdF2 levels from x = y = 0 to x = y = 0.15, while its loss tangent is lower than 0.03. Dielectric permittivity was found to be unaltered over a broad temperature range. According to density functional theory (DFT) analysis, Cd2+ is more likely to occupy the Cu2+ sites in the CaCu3Ti4O12 phase, while Cd2+ replaces Ca2+ ions in the CaTiO3 phase. Impedance spectroscopy findings suggest that the principal source of the tremendous dielectric response in this binary-phase system is an internal barrier layer capacitor composed of semiconducting grains and insulating grain boundaries. According to XPS analysis, electronic charge hopping between Cu+↔Cu2+ and Ti3+↔Ti4+ could be a primary source of n-type semiconducting grains of the CaCu3Ti4O12 phase.