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The dielectric properties of undoped and vanadium (10 mol%) doped SrBi 2 Nb 2 O 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: ϵ r ′ = ϵ∞+ sin (n (T) π /2) ω n(T) − 1 a(T)/ϵ o and ϵ r ″ = σ/ϵ o ω + cos (n (T) π /2) ω n(T) − 1 a(T)/ϵ o . The lattice dielectric constant (ϵ∞) 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.
Acknowledgments
We acknowledge Mr. S. Vynatheya in scanning electron microscopy.
Paper originally presented at AMF-4, Bangalore, India, December 12–15, 2003