Tuning the dielectric and optical properties of Pr–Co–substituted calcium copper titanate for electronics applications

Pr–Co–substituted calcium copper titanate (CCTO) ceramic with chemical composition Ca_1-xPr_xCu_3-yCo_yTi₄O₁₂ (x = 0.0, 0.1, 0.2, 0.3 and y = 0.0, 0.4, 0.5, 0.6) was synthesized by the sol-gel method. The X-ray diffraction patterns indicate that all the synthesized samples exhibit a pure phase of CCTO ceramic with absence of secondary phases such as CaTiO₃ and CuO. The weight losses observed in the thermogravimetric analysis graph cease to occur at 895 °C, indicating the formation of the final CCTO product. Field-emission scanning electron microscopy micrographs show dense and closely arranged faceted grains with the absence of agglomeration and liquid oxide phase. Energy-dispersive X-ray spectroscopy spectra confirm the stoichiometry of the synthesized CCTO ceramic, and Raman analysis rules out the presence of secondary phases; hence, the purity of the synthesized CCTO ceramic is further supported by Raman and energy-dispersive X-ray spectroscopy spectra. The optical band gap increased with Pr–Co substitution, and a maximum value of 3.88 eV was obtained in the sample with x = 0.0/y = 0.0. The dielectric properties are explained on the basis of a Maxwell-Wagner relaxation process. The sample with x = 0.0/y = 0.0 shows the highest room-temperature dielectric constant (4920) at a frequency of 100 Hz. The lowest value of the room-temperature dielectric loss tangent (0.194) at 100 Hz was observed in the sample with x = 0.1/y = 0.4. The Cole-Cole plot indicates that most of the contribution to the dielectric properties of the synthesized CCTO ceramics originates from grain-boundary resistance.