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The pursuit for an appropriate universal scaling factor to satisfy the time-temperature superposition principle for grain and grain boundary responses has been explored in the ac conductivity domain for polycrystalline double perovskite oxides A2HoRuO6 (AHR; A = Ba, Sr, Ca). The samples show different structural phases ranging from cubic to monoclinic with decreasing ionic radii. The degree of distortion in the materials is correlated to the strength of bonding through the bond valence sum (BVS). The conductivity spectra for all the samples obey the power law behaviour. The contribution of different microstructural features to the conduction process is established. Thermal variation of dc resistivity points towards a gradual crossover from nearest neighbour to variable range hopping. The activation energies obtained from dc conductivity, hopping frequency and relaxation frequency show close correlation between the conduction and relaxation mechanisms. The scaled conductivity curves for AHR showed the presence of two different conduction processes with dissimilar activation energies in the grain boundary and grain response regimes. It is thus concluded that a single scaling parameter is insufficient to satisfy the time temperature superposition principle universally when two different thermally activated regions are present simultaneously in the materials.

Mn doping reduced the band gap to 1.72 eV from 2.18 eV which is confirmed from electronic structure calculations. GdFe0.7Mn0.3O3 exhibits 99% Rh-B degradation at 25 minutes. The multiple oxidation states of Fe and Mn enhances the conductivity and Mn doping reduces the barrier width which facilitates the charge transfer process.

The crossover between two different conduction mechanisms (variable range and small polaron hoppings) is probed utilizing a conjunction of thermally varying conductivity and impedance in polycrystalline Pr2NiTiO6 (PNT). A combination of X-ray diffraction (XRD) and Raman spectroscopic investigations authenticates the lower symmetric monoclinic structure for PNT. The conductivity, impedance and relaxation spectra highlight the combined contributions of the electrodes, grain-boundaries and grain microstructures to the carrier dynamics in PNT. The relaxation mechanism has a non-ideal nature with distribution of relaxation times as observed from the dielectric and impedance spectroscopic revelations. The dc resistivity investigation points towards a transition in the conduction mechanism showing a gradual crossover at temperature 490 K, from small polaron hopping to Mott's variable range hopping due to reduced activation energy.