Manipulating dielectric relaxation via anisotropic field deviations in perovskite titanate grain-grain boundary heterostructure: a joint experimental and theoretical venture

Effect of de field is comprehended in impedance, dielectric, admittance and modulus spectra (40 Hz-20 MHz) of solid-state synthesized, polycrystalline calcium, strontium and barium titanate nanoparticles. The phase conformation, stoichiometry, optical and vibrational characteristics are investigated employing XRD-Rietveld analysis, DRS, FTIR and Raman spectra. The real/imaginary parts of impedance, dielectric and related functions are tailored by varying external field in the context of classical energy-storing bottleneck. The field-dependent Nyquist plots are interpreted from a proposed equivalent circuitry to quantify electrically heterogeneous, grain core-grain boundary (GC-GB) resistance correlations. Relaxation times, shape parameters and low/high-frequency limits are tailored following Cole-Davidson and Johnson's equations, that explicate Maxwell-Wagner interfacial polarization (MWIP). Using the modified Kohlrausch-Williams-Watts (KWW) equation, asymmetric broadening in modulus spectra is analyzed to attune the non-Debye relaxations, free from electrode effects. Large polaron hopping conduction is scrutinized using Jonscher's power law to emphasize variable-range and correlated-barrier hopping mechanisms, comprising delocalized/de-trapped carriers. Bias insurgence promotes Debye relaxations, which however suspends switching of the fundamental relaxation channel, leading to a single normalized master modulus curve. Static dielectric tensors, Born effective charges and field-induced charge cloud separation are enunciated via density functional theory (DFT) framework, whereas finite element simulations using experimentally extracted electrical parameters substantiate non-uniform and anisotropic field-diffusion within the GC-GB heterostructure. [GRAPHICS] .