Fractional power-law spectral response of CaCu3Ti4O12 dielectric: Many-body effects

Abstract

Spectral character of dielectric response in CaCu3Ti4O12 across 0.5 Hz–4MHz over 45–200 K corresponding to neither the Debyean nor the KWW relaxation patterns rather indicates a random-walk like diffusive dynamics of moments. Non-linear relaxation here is due to the many body dipole-interactions, as confirmed by spectral-fits of our measured permittivity to the Dissado-Hill behaviour. Fractional power-laws observed in ε*(ω) macroscopically reflect the fractal microscopic configurations. Below ∼100 K, the power-law exponent m (n) steeply decreases (increases), indicating finite length-scale collective response of moment-bearing entities. At higher temperatures, m gradually approaches 1 and n falls to low values, reflecting tendency towards the single-particle/Debyean relaxation.