Synthesis, dielectric properties, and influences oxygen vacancies have on electrical properties of Na1/2Bi1/2Cu3Ti4O12 ceramics prepared by a urea combustion method

The influences of oxygen vacancies on the dielectric and electrical properties of Na1/2Bi1/2Cu3Ti4O12 ceramics prepared using a urea combustion method were investigated via an annealing treatment in an O2 atmosphere. Interestingly, a single Na1/2Bi1/2Cu3Ti4O12 phase was successfully prepared using a low calcination temperature of 800 °C. High dielectric permittivity (e′) and dense ceramic microstructure were achieved by sintering compacted powders at a low temperature of 980 °C. e′ and the loss tangent (tanδ) were decreased by annealing in an O2 atmosphere. This was associated with the oxygen vacancy concentration at grain boundaries (GBs). A decrease in low-frequency tanδ was caused by enhancement of GB resistance, which was due to filling oxygen vacancies at GBs. A slight decrease in e′ was attributed to the reduction in GB capacitance. Through use of an annealing process, the conduction activation energy at GBs was increased, whereas the conduction activation energy inside the grains remained unchanged. These results clearly indicated the effect of oxygen vacancy concentration at the GBs on the giant dielectric response and correlated GB response.