Nanocrystalline samples of La0.5Pr0.2Ca0.3–xBaxMnO3 (LPCBMO) (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) manganites were successfully synthesized by employing prolonged grinding process in conventional solid-state reaction route. The obtained value of crystallite size (CS) varies from 76 nm in lower doped sample (x = 0.05) to 13 nm in the sample doped with Ba2+ (x) = 0.05. The variation in CS with x has been discussed in the context of larger the size mismatch at A-site cationic lattice, larger the structural disorder, higher the control over the crystallinity. The effect of crystallite size and other structural parameters on the transport properties of LPCBMO samples has been discussed in detail in the light of competition between the structural disorder effect and tolerance factor effect on the charge transport mechanism and proven that at nanoscale level also, the tolerance factor is effectively modifying the transport mechanism in manganites.
