Impact of tunable oxygen vacancy on microstructure, conduction mechanism and dielectric properties of Y3+/Mg2+ modified calcium copper titanate ceramics

Pure CaCu 3 Ti 4 O 12 and rare-earth co-doped Ca 1- x Y x Cu 2.95 Mg 0.05 Ti 4 O 12 ( x = 0.02, 0.04, 0.06) ceramics were synthesized by conventional solid state reaction method. X-Ray Diffraction (XRD) peaks confirmed the CaCu 3 Ti 4 O 12 phase formation accompanied by a minor CuO peak around 35.5°. X-Ray Photoelectron Spectroscopy (XPS) was employed to predict the concentration of oxygen vacancies (intrinsic factor) and elucidate the presence of variable oxidation states (Cu 2+ /Cu + and Ti 4+ /Ti 3+ ) in prepared compositions. Photoluminescence (PL) study revealed the presence of blue-UV emission peaks in all samples related to shallow defects whereas the blue-green emission attributed to oxygen vacancies ( V O · , V O · · ), Ti 4+ ↔ Ti 3+ transitions or deep defects. Field Emission Scanning Electron Microscopy (FESEM) revealed that the simultaneous doping of Y 3+ /Mg 2+ at Ca 2+ /Cu 2+ site reduced the grain size from 3.44 μm to 1.78 μm. Transmission Electron Microscopy (TEM) was utilized to determine the grain boundary thickness (t gb ) and reduced from 5.06 nm to 2.14 nm for CCTO and CY6CM5TO ceramic. The impedance studies demonstrated that grain boundary resistance (R gb ) exceeds bulk resistance (R g ) in all prepared samples, which consequently favors the IBLC model (R gb >>R g ). Moreover, the grain boundary resistance enhanced with increasing Y 3+ contents and was reported to be order of 10 6 (Ω) in Ca 0.94 Y 0.06 Cu 2.95 Mg 0.05 Ti 4 O 12 ceramics. It was observed that the simultaneous doping of Y 3+ /Mg 2+ in CCTO host matrix tailored the electrical response of ceramics by improving the dielectric constant (ε') values and minimizing dielectric losses (tanẟ). Ca 0.94 Y 0.06 Cu 2.95 Mg 0.05 Ti 4 O 12 ceramic witnessed the lowest dielectric losses (tanẟ = 0.0079 at 323 K and 1 kHz) making it a promising material for energy storage applications.