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Tuning A-site ionic size in R0.5Ca0.5MnO3 (R = Pr, Nd and Sm): robust modulation in dc and ac transport behavior

Structural investigations on Pr0.5Ca0.5MnO3, Nd0.5Ca0.5MnO3 and Sm0.5Ca0.5MnO3 display a systematic tuning in orthorhombic distortion which appears due to a change in A-site ionic size. Comprehensive investigations on dc conduction using various models indicate strong correlation with structural changes. Careful analysis of the ac conductivity mechanism as a function of frequency and temperature brings out a pronounced effect of structural modifications on the polaron conduction mechanism. Contrary to typical manifestations, dc conductivity and relaxation of charge carriers reveal non-Arrhenius behavior. This work provides a detailed and systematic addition to the phase diagram of electronic transport in the rare-earth manganite system doped with a divalent alkali atom.