MICROWAVE DIELECTRIC-PROPERTIES AND PHONON CHARACTERISTICS FOR BA(MG13TA2/3)O-3-A(MG1/2W1/2)O-3 (A=BA, SR, AND CA) CERAMICS/

The microwave dielectric properties and the polar lattice vibrations w ere 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 GKz. In order to better understand the dielectric los s mechanism, the characteristics of the polar lattice vibrations were analyzed by using infrared reflectivity measurements. The results sugg est 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 pote ntial anharmonicity caused by the A-site cation substitutions and to t he 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 d ielectric constants calculated from the reflectivity spectra were cons istent with those measured at 10 GHz. However, for Ba(Mg1/3Ta2/3)O-3-C a(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 s upposed that these behaviors are partly due to the Debye-like losses c aused by the defect dipoles formed by the incorporation of Ca into the B-site sublattice.