Alternating-current conductivity and dielectric permittivity of polyaniline doped with β-naphthalene sulphonic acid

The alternating-current (ac) conductivity σ(ω) and the dielectric permittivity of polyaniline doped with β-naphthalene sulphonic acid (NSA) have been extensively studied in the temperature range of 300 K to 80 K and in the frequency range of 500 Hz to 10 MHz. The ac conductivity follows a power law in frequency, σ(ω) α ω^s, at high frequency, where s (≃0.85-0.88) is nearly independent of temperature. At low temperature the ac conductivity spectra show saturations for frequencies of the order of 10⁶ Hz. The ac conductivity exhibits a scaling behaviour in the form σ(ω)/σ₀ = 1 + (ω/ω₀)ⁿ with 0.8 < n < 0.9. The dielectric loss spectra reveal two peaks corresponding to two plateaus of σ(ω) at low and high frequencies. The broad and asymmetrical loss peaks of the dielectric spectra have been analysed on the basis of stretched- exponential decay of the electric field, φ(t) = exp - (t/τ₀)^β, where 0 < β ≤1. The loss spectra at low temperatures collapse onto a single scaling curve determined by the height and position of the peak.