Microwave dielectric properties and characteristics of polar lattice vibrations for Ba(Mg1/3Ta2/3)O3-A(Mg1/2W1/2)O3 (A = Ba, Sr, and Ca) ceramics

The microwave dielectric properties and the polar lattice vibrations were investigated for complex perovskite-structured Ba(Mg1/3Ta2/3)O-3-A(Mg1/2W1/2)O-3 (A = Ba, Sr, and Ca) ceramics. With 0.5 mol % Ba(Mg1/2W1/2)O-3 content, the dielectric quality factor, Q(d), reached the maximum of 40 000 at 10 GHz. In order to better understand the dielectric loss mechanism, the characteristics of the polar lattice vibrations were analyzed by using infrared reflectivity measurements. The results suggest that the intrinsic dielectric loss mechanism for Ba(Mg1/3Ta2/3)O-3-A(Mg1/2W1/2)O-3 can be attributed to the increase in the crystal potential anharmonicity caused by the A-site cation substitutions and to the phonon degeneracy or coupling due to the incorporation of Mg and W into the B-site sublattice of Ba(Mg1/3Ta2/3)O-3. For Ba(Mg1/3Ta2/3)O-3-Ba(Mg1/2W1/2)O-3 and Ba(Mg1/3Ta2/3)O-3-Sr(Mg1/2W1/2)O-3 the complex dielectric constants calculated from the reflectivity spectra were consistent with those measured at 10 GHz. However, for Ba(Mg1/3Ta2/3)O-3-Ca(Mg1/2W1/2)O-3, the difference between the calculated and measured Q values became larger with increasing Ca(Mg1/2W1/2)O-3 content. It is supposed that these behaviors are partly due to the Debye-like losses caused by the defect dipoles formed by the incorporation of Ca into the B-site sublattice. (C) 1999 American Institute of Physics. [S0021-8979(99)09202-6].