Computational investigation of dielectric absorption at microwave frequencies in binary oxides

In this work, a computational study of the dielectric absorption and Q-factor at microwave frequencies in rocksalt oxides is presented. This work is performed within a theory for the two-phonon anharmonic absorption process in terms of third-order force constant matrices, phonon eigendata, and Born effective charges. The complex dielectric permittivity is expressed by means of Green’s functions. This theory is used on model systems that are described using empirical Buckingham potentials with shells. The Q-factor and its temperature dependence in AO (A=Mg, Ca, Ba, Sr) oxides with the rocksalt structure is calculated. For MgO, the calculated Q-factor at room temperature agrees relatively well with experiments, and the temperature dependence is in qualitative agreement. The Q-factor in a model “AO” system is also calculated to determine the effects of cation mass and size on the Q-factor. Increased cation size is found to lower the Q-factor, whereas increasing cation mass is found to increase the Q-factor when the cation mass is higher than that of Ca.