Impact of tunable oxygen vacancy on microstructure,conduction mechanism and dielectric properties of Y^(3+)/Mg^(2+)modified calcium copper titanate ceramicsOA

Pure CaCu_(3)Ti_(4)O_(12)and rare-earth co-doped Ca1-xYxCu_(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 3.44μm to 1.78μm.Transmission Electron Microscopy(TEM)was utilized to determine the grain boundary thickness(tgb)and reduced from 5.06 nm to 2.14 nm for CCTO and CY6CM5TO ceramic.The impedance studies demonstrated that grain boundary resistance(Rgb)exceeds bulk resistance(Rg)in all prepared samples,which consequently favors the IBLC model(Rgb>>Rg).Moreover,the grain boundary resistance enhanced with increasing Y^(3+)contents and was reported to be order of 106()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.