Novel high capacitance materials:- BaTiO3:La and CaCu3Ti4O12

A review is given of the origins of high permittivity in two groups of materials, La-doped BaTiO3 and a new barrier layer capacitor material, CaCu3Ti4O12. Factors that influence permittivity include: dopant, doping mechanism, processing conditions and grain size. La-doped BaTiO3 has high permittivity due to its ferroelectric nature at low temperatures and a novel doping mechanism: A-site substitution linked to the creation of B-site vacancies for charge compensation. Permittivities of 25,000 have been achieved, which can be increased further to ∼36,000 by additional doping with Zr. The value of impedance spectroscopy to characterize materials that have heterogeneous electrical microstructures is illustrated with the example of CaCu3Ti4O12; the high permittivity is not a bulk effect, as widely stated in the literature, but is a thin layer effect typical of a barrier layer capacitor. By attention to processing conditions to achieve large grain sizes, effective permittivities as high as 300,000 have been obtained.