Almond-West type grain and grain boundary conduction-modified dielectric relaxation in NdCoO₃

In this present work, the bulk NdCoO₃ was prepared via conventional solid-state synthesis route and its single-phase formation with a cubic crystal structure of space group Pm anti 3m [No. 221] were investigated with a perspective to understand its grain and grain-boundary contribution in dielectric and conduction processes. A general equation for grain and grain-boundary contribution in conduction-modified dielectric relaxation processes for ionically conducting material was proposed the first time and also correlated with our experimental observation, ε(ω)_total = ε_∞ + (ε_s-ε_∞)/(1+((iω)/(ω_r))^1-α) + (σ₀)/(ε_0ω)[1 + i((ω)/(ω_h))^n₁ + i((ω)/(ω_h))^n₂] where (ω_r, α), (ω_h, n₁) and (ω_h, n₂) couples explain the lattice and charge carriers responses for grain and grain boundary respectively. The relaxation-type conduction-modified dielectric behavior was observed from low to high-frequency region (100 Hz-1 MHz) and fitted conduction spectra with modified Jonscher power law which reveals the existence of grain and grain boundary effect with dc activation energy 0.86 eV. The impedance response was resolved into two contributions associated with intra-grain (bulk) and inter-grains (grain boundary) and the grain boundary resistance and capacitance exhibit a higher value than its grain counterparts. The suppressed and asymmetric semicircle in the Cole-Cole plot of impedance confirms the existence of the non-Debye-type of relaxation in NdCoO₃. (orig.)