Complex permittivity characterization of double oxides of the perovskite crystal structure

Perovskite mineral structure is cubic, with one formula-weight per unit cell. Its name was given by the mineral CaTiO₃. A large number of double oxides (as well as some iodates and double halides) are classified as belonging to this type. In this work the dielectric properties of perovskite crystals are presented, namely the complex permittivity (real and imaginary part) and the loss factor (tan delta). Their values in the 20 Hz-1 MHz frequency range were obtained using the equivalent capacitance-conductance parallel circuit method. Specimens were prepared by mixing TiO₂ (of predominantly anatase structure) and CaCO₃ (calcite) powders and compressing them uniaxially to form pellets. These were sintered at temperatures as high as 1200 degC. According to the XRD results obtained, not only did the anatase convert to rutile and the calcite to lime (CaO), but also the double oxide CaTiO₃ was formed, as in the natural perovskite mineral. Its formation was related to higher dielectric constant values and significantly lower losses compared to specimens sintered at lower temperatures, where the perovskite structure was less intense. Such high-K and low-loss dielectric materials have lately found significant attention in the quest of smart antennas for telecommunication applications