Giant dielectric response and low dielectric loss in Al_2O_3 grafted CaCu_3Ti_4O_(12) ceramics

摘要

This study sheds light on the effect of alumina on dielectric constant and dielectric loss of novel CaCu_3Ti_4O_(12) composite ceramics. Alumina, at several concentrations, was deposited on the surface of CaCu_3Ti_4O_(12) particles via sol-gel technique. The dielectric constant significantly increased for all frequencies and the dielectric loss substantially decreased for low and intermediate frequencies. These observations were attributed to the change in characteristics of grains and grain boundaries. It was found that the insulating properties of the grain boundaries are improved following the addition of Al_2O_3. The relative density of CaCu_3Ti_4O_(12)/Al_2O_3 composite ceramics decreased compared to the pure CaCu_3Ti_4O_(12) and the grain size was greatly changed with the alumina content affecting the dielectric properties. With the addition of alumina into CaCu_3Ti_4O_(12), tighter interfaces formed. The 6%- and 10%-alumina ceramics showed the minimum dielectric loss and the maximum dielectric constant, respectively. Both the dielectric constant and loss tangent decreased in the 20%-alumina ceramic due to the formation of CuO secondary phase. It was revealed that Al serves as an electron acceptor decreasing the electron concentration, if Al~(3+) ions substitute for Ti~(4+) ions, and as an electron donor increasing the electron concentration, if Al~(3+) ions substitute for Ca~(2+) ions. We established a processing-microstructure-properties paradigm which opens new avenues for novel applications of CaCu_3Ti_4O_(12) composite ceramics.