Dielectric and Relaxor Properties of Ba_9MNb_(14)O_(45) Ceramics

摘要

The ceramics with two types of nominal compositions including (6:1:4.5) Ba_6M~(2+)Nb_9O_(29.5) and (9:1:7) Ba_9M~(2+) Nb_(14)O_(45) (M = Mg, Co, Zn) have been synthesized and studied with regard to their phase composition and dielectric properties. The materials with Ba_6M~(2+)Nb_9O_(29.5) nominal compositions corresponded to the two-phase region containing 9:1:7 tetragonal tungsten bronze-type (TTB) phase and the 3:1:1 perovskite Ba (M~(2+) _(1/3)Nb_(2/3))O_3. In contrast, 9:1:7 TTB ceramics were near single phase. All of the studied 9:1:7 TTB phases exhibited high values of dielectric permittivity (ε = 800-1100) together with strong frequency dispersion. The observed dispersion of permittivity was accompanied by the monotonic rise of dielectric loss. The dielectric spectra of 9:1:7 TTBs demonstrated a typical relaxor behavior. At low temperatures (100-300 K), two relaxation modes have been found in the tan δ (7) dependencies, which can be associated with two different types of structural disorder in the TTB crystal lattice.