Dielectric properties of stabilized barium titanate films

Abstract

Barium titanate, because of its exceptionally high dielectric constant, has been used extensively as a capacitor material. It, however, possesses two undesirable characteristics, namely decreased insulation resistance (degradation) under high dc voltage stresses at temperatures in excess of the Curie point of 120 [/spl deg/C] and a high-temperature coefficient of capacitance near the Curie point. In the present investigation improvement in life-time were achieved by the incorporation of lanthanum oxide into barium titanate. Films of composition 99 mole % BaTiO/sub 3/ and 0.3 mole % La/sub 2/O/sub 3/ were prepared by the sol-gel method using metal alkoxides, and tested for high-temperature stability. It was found that the resistance of barium titanate to the degradation of dielectric properties can be improved by the incorporation of small quantities (0.1/spl sim/0.5 mole %) of La/sub 2/O/sub 3/. A survey of dielectric properties for compositions forming lanthanum-barium titanate solid solutions indicated that the, temperature coefficient of capacitance and dissipation factor can be reduced to quite low values for certain compositions along the join BaTiO/sub 3/-La/sub 2/O/sub 3/. The compositions containing 0.3 mole % La/sub 2/O/sub 3/ exhibit the most satisfactory dielectric properties but abbreviated lifetimes.