Distinct dominant dielectric relaxation mechanisms in CaCu3Ti4O12 – LaMO3 (M = Mn and Fe) perovskite oxide solid solution

Abstract

Two synthesized perovskite oxide solid solutions, CaCu3Ti4O12 – LaMnO3 and CaCu3Ti4O12 – LaFeO3, possess a crystalline structure embracing an amalgamation of two distinct phases, namely, hexagonal and orthorhombic phases in CaCu3Ti4O12 – LaMnO3 and cubic and orthorhombic phases in CaCu3Ti4O12 – LaFeO3. Examination of dielectric properties reveals colossal dielectric constant (εr), the peak magnitude of εr at 1 kHz being approximately 6×103 and 2.5×104 for Mn and Fe based compound, respectively. Further, complex impedance investigation (CII) establishes the activation energy (Ea) of grains (0.21 eV and 0.07 eV for Mn and Fe based solid solution, respectively) and grain boundaries (0.19 eV and 0.19 eV for Mn and Fe based solid solution, respectively). The deviation in Ea of grains and grain boundaries, as established through CII, in both, Mn and Fe based samples validates the existence of Maxwell-Wagner (M − W) relaxation. The AC conductivity spectrum for both the samples obeying the Jonscher's universal power law (JUPL): σ(ω,T)=σdc+Aωn. The Ea of bulk samples (0.37 eV and 0.19 eV for Mn and Fe based solid solution, respectively) authenticates predominant M − W relaxation (interfacial polarization) with polaron hopping playing the secondary role in Mn based sample, while both, polaron hopping and M − W relaxation being identical contributors towards dielectric nature of Fe based sample.