Frequency Dependent Dielectric Characteristics of Undoped and Vanadium-Doped SrBi_2Nb_2O_9 Ferroelectric Ceramics: A Comparative Study

摘要

The dielectric properties of undoped and vanadium (10 mol percent) doped SrBi_2Nb_2O_9 ferroelectric ceramics were studied in the 100 Hz to 1 MHz frequency range at various temperatures (300-823 K). The dielectric constants of vanadium doped ceramics were higher than those of undoped ceramics. A strong low frequency dielectric dispersion (LFDD) was encountered in these ceramics in the 573-823 K temperature range. The dispersion was stronger at low frequencies and higher temperatures for vanadium -doped ceramics. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonscher's dielectric dispersion relations: epsilon_r' = epsilon_(infinity) + sin (n (T) pi/2) omega~(n(T)-1) a(T)/epsilon_o and epsilon_r" = sigma/epsilon_0 omega + cos (n (T) pi/2) omega~(n(T)-1) a(T)/epsilon_o. The lattice dielectric constant (epsilon_(infinity)) shows a peak at T_c. The coefficient A(T)( = a(T)S/L) and the exponent n (T) of the Jonscher's expression were, determined. The exponent n (T) was found to be minimum at the Curie temperature, T_c. The value of n for the vanadium-doped samples was less than that of the undoped one. The parameter A(T), which indicates the polarizing power, showed a prominent peak in the vicinity of the Curie temperature for both the samples. However, the value of A for the vanadium-doped samples was higher than that of undoped SBN ceramics.