Application of High Permittivity Bismuth Copper Titanate in Multilayer Capacitors

Abstract

A nonferroelectric high permittivity compound with the perovskite structure, Bi2/3Cu3Ti4O12, was synthesized at 900 ◦C. The ceramic powder and appropriate organic additives were used for preparation of a slurry for tape casting. The obtained green tapes were smooth, flexible, and with a uniform thickness of 25 μm after drying at 50 ◦C. Ag electrodes were screen printed on green rectangular sheets cut by a laser. Subsequent operations were screen printing of Ag internal electrodes, stacking of green sheets, isostatic lamination, cutting, deposition of external terminations and co-firing of dielectric and conductive layers at 850 ◦C. Scanning electron microscopy observations showed well sintered, dense, fine-grained microstructure of ceramic layers and good cooperation with the electrodes made of commercial Ag paste. Capacitance and dissipation factor of multilayer capacitors were examined in the temperature range from −55 to 330 ◦C at frequencies 10 Hz–2 MHz. The fabricated multilayer capacitors exhibit high capacitance and relatively low temperature coefficient of capacitance in the temperature range from −55 to 110 ◦C. The obtained lead-free high permittivity nonferroelectric material Bi2/3Cu3Ti4O12 is a spontaneously formed internal barrier capacitor. This material seems to be a promising alternative for conventional lead-based relaxor dielectrics in multilayer ceramic capacitors.