High Temperature Sodium Bismuth Titanate Capacitors - A New Product Realized

This paper describes the development of a lead free, high temperature ceramic capacitor material having the base composition of (Na-0.5 Bi-0.5) TiO3. The goal is to modify this structure to create a material that has the relative permittivity of barium titanate with extended X7R-like properties to 250 degrees C -an X14R. After an extensive compositional and theoretical modeling investigation a composition was selected and capacitors developed. The dielectric has a 1-kHz relative permittivity of similar to 1200 with <+/- 15% variation from -25 to +250 degrees C and <5% loss from -55 to +250 degrees C. These capacitors also have very low voltage coefficients, indeed they are positive at the low end of the temperature range, resulting in a combined T-C-Vc capacitance variation 0%/-25% of nominal from -55 to +200 degrees C with applied voltage stress from 20 to 260 V/mil.