Mechanism of the effect of Al and Sr substitution on the electrical resistance in CaCu3Ti4O12 ceramics

To investigate the mechanism of Al and Sr substitution on grain resistance (Rg) and grain boundary resistance (Rgb) in CaCu3Ti4O12 (CCTO) ceramics, various compositions of Ca1-xSrxCu3Ti4-yAlyO12 (x = y = 0; x = 0, y = 0.04; x = 0.6, y = 0; x = 0.6, y = 0.04) ceramics were synthesized. All samples exhibited excellent dielectric loss and breakdown field strength performance. These improvements can be attributed to the substantial rise in Rgb and an unconventional boost in Rg. Activation energy tests and X-ray photoelectron spectroscopy analysis indicate that both Rgb and Rg are strongly influenced by oxygen vacancies (V center dot center dot O) and the mixed structures of Cu+/Cu2+ and Ti3+/Ti4+. This study explains the mechanism of Al and Sr substitution based on atomic electronegativity, with Al inhibiting the formation of Cu+ and Ti3+ but promoting the generation of V center dot center dot O, while Sr inhibiting the formation of Ti3+ and V center dot center dot O but promoting the generation of Cu+. This research offers valuable theoretical instructive for the design of high-resistivity CCTO ceramics.