Two‐Phase Ceramic Dielectrics

Two-phase dielectrics composed of a high dielectric constant phase (BaTiO 3 ) in combination with a high dielectric strength and low-loss phases have been investigated as candidates for high-voltage capacitors on Navy electrically powered systems. Second phase materials included BaO.Al 2 O 3 .2SiO 2 , MgAl 2 O 4 , and MgO, which showed good chemical compatibility with BaTiO 3 . Solid solubility was observed in the BaTiO 3 - LaAlO 3 system. The optimum sintering conditions were determined for each system, and the phase composition, microstructure, and dielectric properties of the composite materials were characterized. A significant decrease in changes of dielectric constant and volume changes at transformation temperature, as well as the shift of T c were observed for all the systems and related to stresses between the phases as a result of differences in the properties of the components. A decrease in the tetragonality of BaTiO 3 was also observed. The experimental dielectric data show that no single theoretical model can describe the behavior of two-phase materials in all the systems studied. However, they are all in the desirable range showing promise for development of capacitors utilizing the advantageous properties of the components.