Microwave dielectric permittivity of NaTaO3 ceramics exhibits increase on cooling and saturation at low temperatures, which is typical for incipient ferroelectrics. The temperature dependence of permittivity was successfully fit with the Barrett formula and explained by polar phonon behaviour detected in infrared and THz spectra. Solid solution of NaTaO3 with Na0.5Bi0.5TiO3 (NBT) exhibits increase of both permittivity and dielectric loss with rising Na0.5Bi0.5TiO3 concentration. This is caused by increasing contribution of dielectric relaxation seen in THz dielectric spectra. The relaxation relates to dynamics of polar nanoclusters and ferroelectric domains in NBT cermics.
COBISS.SI-ID: 25942823
The dependence of the dielectric permittivity on the uniaxial compressive stress was investigated for the case of Na0.5Bi0.5TiO3–KTaO3 ceramics. The results were connected with the transition from the ferroelectric to the relaxor state in the concentration region between 5 and 10 mol% of KTaO3. With this transition, the permittivity–stress dependence changes from non-linear, irreversible and time dependent to linear, instantaneous and reversible. In samples with 10–30 mol% of KTaO3 some minor relaxations were observed, which were suppressed under a small pre-stress. The stress sensitivity was higher at a lower measuring frequency and the reversible change of the permittivity was the highest in the sample with 20 mol% of KTaO3 (the absolute and relative changes of permittivity were 196.5 and 10.3%, respectively, at a pressure change between 8 and 219 MPa).
COBISS.SI-ID: 26421543
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 (e = 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.
COBISS.SI-ID: 26132519