A novel composite superionic system, [Ag2HgI4:0.2AgI]:xCuI, (x = 0.2, 0.4, 0.6 mol. wt.%), was prepared and [Ag2HgI4:0.2AgI] mixed system was used as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100 Hz, 120 Hz, 1 kHz, and 10 kHz in the temperature range 90°–170°C by a Gen Rad 1659 RLC Digibridge. Sharp increase in conductivity was observed for β-α phase transitions. As a result of increase in the dopant-to-host ratio, the conductivity of the system exhibited Arrhenius (thermally activated)-type behavior. X-ray powder diffraction, differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) studies confirmed the doping effect on the transition in the host, the phase transition temperature increased with an increase in the dopant concentration. Activation energies for the system in eV both for the pretransition and post-transition phase transformations are reported. The addition of CuI to [Ag2HgI4:0.2AgI] shifted the phase transition of the host [Ag2HgI4:0.2AgI], due to an interaction between [Ag2HgI4:0.2AgI] and CuI.
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