Ferroelectric and Ferromagnetic Glass Ceramics for Microwave Applications

Conventional ferroelectric and ferromagnetic ceramics are crystalline ceramics. The amount of crystalline phase is almost closed to hundred percent. The introduction of a small amount glass phase or other second phase will much reduce the dielectric permittivity and the magnetic susceptibility of the materials. However, in many cases such as microwave applications, high permittivity and high susceptibility are not preferable to the requirements. In many cases, very complicated and comprehensive requirements of electric, magnetic, mechanic behaviors are of much importance to the specific applications. The processing requirements to the materials such as co-firing of the material with other materials and/or electrodes, sometimes dominates the selection of materials. A new group of microcrystalline ferroelectric and ferromagnetic glass ceramics is introduced to meet such special requirements. Most major ferroelectrics and ferromagnetics can be prepared as glass ceramics by using sol-gel technology. The glass content of the glass ceramics can be adjusted in very wide range from less than a few percent to more than ninety percent. The size of ferroic crystallites can be controlled in the range from nanometer sizes to micrometer sizes. The electric and magnetic behaviors of the glass ceramics will mostly inherit from the crystalline components, while the mechanical and thermal processing behaviors will be mostly depending on the glass components. The electric, magnetic, elastic, and thermal behaviors of the glass ceramics can be tailored in much wider range compare to crystalline counter parts. The ferroic glass ceramic can be prepared in the form of bulk ceramics, thick and thin films. There are a lot of advantages of glass ceramics, such as low densification temperatures, fine and dense microstructures, low specific density, low acoustic impedance, low and adjustable thermal expansion, good mechanical strength and toughness, better temperature and frequency stability of dielectric/magnetic behaviors. Discuss of the idea to develop the ferroelectric and ferromagnetic glass ceramics will be given in this presentation. Examples of the processing and microwave applications of the materials will be also given.