Abstract
The ionic conductivity of (1-x)Me2SO4:(x)Mr2(SO4)3 (where Me = Ag, Li, Na, and Mr = Y, La, Sm, Gd and Dy with x = 0.025-0.09) is investigated using complex impedance spectroscopy. The solid solubility limits up to x = 0.0563 of Mr2(SO4) in -Me2SO4 is established by x-ray powder diffraction. The solute Me2SO4 lattice undergoes an expansion/contraction upon partial replacement of the Me+ with relatively bigger/smaller guest cations. The activation enthalpy for ion migration is found to decrease commensurably with the distortion factor r = rg-rh (rg and rh being the ionic radii of the guest and host cations, respectively). Concurrently, enhancement in conductivity is observed. The maximum in conductivity (minimum activation enthalpy) is found at about 6-7% vacancy in all the three systems. The vacancies created to compensate the electric charge imbalance together with the lattice distortion chiefly govern the conductivity behaviour. In addition, the electronic polarizabilities of the dopant cations are seen to play a crucial role. The results are discussed by considering ion percolation model.
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