Atmosphere-driven microstructural and dielectric tuning in CCTO ceramics

Calcium copper titanate (CCTO) ceramics are strong candidates for solid-state energy storage due to their high dielectric constant, which is closely linked to microstructural features such as secondary phases and grain size, also structural defects, such as oxygen vacancies or cation substitutions. This study investigates how different sintering atmospheres (air, helium, hydrogen, and oxygen) affect the microstructure, structure and dielectric properties of CCTO ceramics. SEM analysis revealed that helium and hydrogen atmospheres favor larger grains and broader size distributions, while oxygen prevents significant grain growth and reduces secondary phases. Impedance spectroscopy indicated a direct correlation between sintering atmosphere and dielectric behavior. The highest dielectric constant (∼37,600) with low dielectric loss (tanδ = 0.10) at 1 kHz was achieved for samples sintered in helium, attributed to synergistic effects of grain growth and oxygen vacancy that caused an increase in the conductivity of the grain and the increase in the resistivity of the sub-grain and grain boundaries. The near-constancy of grain activation energy ( = 0.091–0.112 eV), across all sintering atmospheres, provides compelling evidence for percolation-dominated transport within the grains. These results highlight the importance of atmosphere control during sintering to tune CCTO microstructure and optimize dielectric performance for advanced capacitor applications.