Research trends in microwave dielectrics and factors affecting their properties: A review

Ceramists are constantly looking for materials to be used as dielectric resonators in the telecommunication industry. These applications require materials with epsilon(r) similar to 4-120, Q x f(0) > 10000 GHz and tau(f) similar to 0 ppm K-1. Additionally, efforts are also underway to lower the sintering temperatures (e. g. <= 800 degrees C) to reduce processing and electrode costs. The simultaneous achievement of all the three properties mentioned above is difficult; nevertheless, some materials have been synthesized fulfilling the criteria for microwave applications. This study is an overview of various studies on materials for possible applications as microwave dielectrics and factors affecting their microwave properties. These factors include crystal structure, defects, fabrication route, and the type and concentration of substituents and additives.