MICROWAVE CERAMICS T. Siegrist, T.A. Vanderah, R.S. Roth, Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974 NIST, Ceramics Division, Gaithersburg, MD 20899

Modern wireless communication systems incorporate oxide ceramics with unique electrical properties. Cellular phones, for instance, may contain up the 14 individual pieces of ceramics, mainly as filters. Magnetic ceramics are used where device action is controlled via an external magnetic field. For this purpose, magnetic ions have to be incorporated in good dielectrics. This has led to the detailed study of the Ba-Ti-Fe-O phase diagram. New phases based on hexagonal perovskites where found. These phases can be described by combining octahedra and tetrahedra, resulting in complex stacking sequences. The crystal chemistry of various new phases will be discussed.