Studies of the impact of copper doping on the electric, dielectric, and conduction mechanism of calcium titanate prepared by sol–gel process

This study presents a comprehensive investigation into the effects of copper substitution on the structural, microstructural, and electrical properties of Ca_1−xCu_xTiO₃ samples synthesized via the sol–gel method. Through a systematic examination of samples with x = 0 (CTO), x = 0.04 (CCTO_0.04), and x = 0.08 (CCTO_0.08), novel insights into their behavior are revealed. X-ray diffraction analysis and Rietveld refinement confirm that all samples crystallized in the orthorhombic Pbnm space group, with copper-doped samples exhibiting a minor secondary cubic phase due to the incorporation of Cu²⁺ into the CaTiO₃ lattice. Microstructural investigations reveal significant changes induced by copper substitution, including the formation of a liquid phase. Energy-dispersive X-ray spectroscopy (EDS) point mapping near grains and grain boundaries unveils copper segregation, with Cu preferentially integrating into the grains rather than the grain boundaries. This copper distribution within the microstructure is likely to influence the material’s overall electrical properties. Impedance spectroscopy reveals a unified relaxation process associated with grain behavior at temperatures below 340 K, indicated by the presence of a single semicircle in the impedance spectra. However, at temperatures above 360 K, two distinct semicircles emerge, signifying the coexistence of dual relaxation mechanisms, one associated to grains and the other to grain boundaries. Analysis of alternating current (AC) conductivity (σ_ac) as a function of temperature and frequency reveals that the substitution of Ca²⁺ with Cu²⁺ significantly alters the electrical behavior of the material, with CCTO_0.04 and CCTO_0.08 showing enhanced conductivity and reduced activation energy. The activation energy values suggest that conduction in these materials is primarily governed by the migration of simply ionized oxygen vacancies. These findings emphasize the critical role of copper dopant concentration in modulating the electrical properties of CCTO, offering valuable insights for applications in electronic devices, where precise control of electrical conductivity and dielectric behavior is essential.