High frequency dielectric properties of CaTiO3-based microwave ceramics

We have investigated the far-JR, submillimetre and microwave (MW) dielectric response of CaTiO3 (CT)-Sr(Mg1/3Nb2/3)O-3 (SMN), CT-Sr(Zn1/3Nb2/3)O-3 (SZN), CT-NdAlO3 (NA) and CT-LaGaO3 (LG) solid solutions ceramics series. The contribution of extrinsic losses has been analysed by extrapolation of the far-IR and terahertz dielectric data down to the MW range and comparison with directly measured data. This procedure has also been justified by comparing the losses in CT and LG ceramics with the losses in their crystalline forms published in the literature. The compositional dependences of the permittivity and temperature coefficient on the resonance frequency have been analysed and fitted by appropriate expressions. We have found that in the case of CT-NA and CT-LG ceramics, the best fits can be obtained using a Clausius-Mossotti equation with linearly mixed polarizabilities. On the other hand, for CT-SMN and CT-SZN ceramics the Lichtenecker logarithmic rule and the Hashin-Shtrikman expression have been used. We explain this difference as a consequence of the different character of short-range ordering in the studied ceramic systems.