Microwave dielectric losses caused by lattice defects

Dielectric loss tangent at microwave frequency is mainly determined by the anharmonic terms in the crystal's potential energy. In addition, there is a kind of lattice defect that increases the dielectric loss tangent seriously. This paper presents the experimental results for two materials; the system Ba(Zn,Ta)O3–BaZrO3 and (Zr,Sn)TiO4. The dielectric loss tangents of the system Ba(Zn,Ta)O3–BaZrO3 increases seriously when the B-site ions distribute disorderedly in the crystal. The doping of oxygen vacancies and acceptor ions in (Zr,Sn)TiO4 increase tan δ by the way they increase the gradient and intercept of linear frequency dependency of tan δ. These experimental results are reasonably explained by Schlömann's theory. He predicted that the dielectric loss tangent increases when the ions are distributed disorderedly in a way that they break the periodic arrangement of charges in the crystal, and that the increase of tan δ is negligible if the disordered charge distribution maintains the charge neutrality within a short range of the lattice constant in the crystal.