The ceramics with two types of nominal compositions including (6:1:4.5) Ba6M2+Nb9O29.5 and (9:1:7) Ba9M2+Nb14O45 (M = Mg, Co, Zn) have been synthesized and studied with regard to their phase composition and dielectric properties. The materials with Ba6M2+Nb9O29.5 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(M2+1/3Nb2/3)O3. 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 (T) dependencies, which can be associated with two different types of structural disorder in the TTB crystal lattice.
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