Relaxation Effects in Nonstoichiometric NBT-Based Ceramics

Effects of cation nonstoichiomtry on crystal structure parameters, microstructure, and dielectric properties of ceramics (Na0.5+xBi0.5)TiO3 and (Na0.5-xBi0.5)TiO3 with Bi/Na<1 and of solid solutions [(Na0.5Bi0.5)1-xKx]TiO3 and (Na0.5Bi0.5)(Ti1-xMgx)O3 with x = 0 – 0.1 have been studied. Changes in the unit cell parameters and microstructure of the samples observed in ceramics prepared correlate well with both preparation conditions and radii of substituting cations. Ferroelectric phase transitions near ~ 400 K and ~ 600 K were confirmed ib the systems studied. Phase transitions near ~ 400 K demonstrate a pronounced relaxor behavior determined by the presence of polar regions in a nonpolar matrix. Besides, additional anomalies related to presence of relaxing dipoles formed by oxygen vacancies were observed on temperature dependences of dielectric permittivity at temperatures higher than 700 K. The results obtained confirmed that increase in nonstoichiometry lead to increase in ionic conductivity of the samples.

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