in CaCu₃Ti₄O₁₂ ceramics (arising from a semiconducting grain/insulating grain boundary microstructure) has been revealed by impedance spectroscopy of ceramics sintered for 3 and 24 h: a rise in permittivity from 9000 to 280 000 was found. The easy-to-prepare CaCu₃Ti₄O₁₂ is a hot candidate for ceramic capacitor applications. (D. C. Sinclair et al., September 16, Adv. Mater. 2002, 14, 1321-1323)