The results of the studies on structural disorder-induced modifications in the transport behaviour of La$_{0.5}$Pr$_{0.2}$Ca$_{0.3−x}$Ba$_x$MnO$_3$ (LPCBMO) ($0.05 ≤ x ≤ 0.30$) manganites were reported. Structural studies using X-ray diffraction (XRD) measurements confirmed the single phasic nature of all the samples without any detectable impurities. The A-site size disorder ($σ_2$ A) increased from $3.81 \times 10^{−5} (x = 0.05)$ to $14.9 \times 10−5 (x = 0.30)$. With the increase in structural disorder in LPCBMO system, the transport improved for the range: $0.15 ≤ x ≤ 0.30$, which can be ascribed to the enhancement in one electron bandwidth which dominates over the structural disorder effect, while for lower values of $x$, strong competition existed between size disorder and one electron bandwidth. Below 50 K, all $\rho–T$ plots showed resistivity minimum behaviour, which modified with disorder. This behaviour wasdiscussed in detail on the basis of electron–electron interaction having the form: $\rho = [1/(\rho_0 + BT^{1/2})] + \rho_nT_n$. Variation in temperature sensitivity with disorder was also discussed in context of granular morphology and phasesegregation scenario.

In this communication, structure and charge, conduction mechanisms have been understood for sol–gel grown nanostructured La$_{0.6}$Nd$_{0.1}$Sr$_{0.3}$MnO$_3$ (LNSMO) manganites prepared at different process temperatures under air and oxygen environments. Obtained X-ray diffraction patterns of all the samples were analysed using Rietveld refinements and obtained structural lattice parameters have been discussed in correlation with resistivity behaviour of the samples. Observed low temperature resistivity upturn behaviour has been examined in the context of electron–electron scattering mechanism. Metallic and insulating/semiconducting behaviours of all the nanostructured LNSMO manganites have been understood by using various models and mechanisms. Magnetoresistance isotherms have also been theoretically fitted and separate grain and grain boundary contributions have been studied for LNSMO manganite samples. Allobtained fitting parameters have been discussed in the context of role of applied magnetic field, process temperature and annealing environment.