5.
The compositions (1 −
x)Ag
2SO
4−(
x)BaSO
4, where
x=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba
2+ in Ag
2SO
4 was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained
using a detailed impedance analysis. The partial substitution of Ba
2+ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model
based on lattice distortion (expansion) due to partial substitution of Ag
+ by the bigger Ba
2+ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO
4-dispersed Ag
2SO
4 conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the
light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO
4 dispersed Ag
2SO
4 is due to percolation threshold.
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