Structural, morphological, magnetic and electrical properties of La0.8Na0.2-x □ x MnO3 (0.00 ≤ x ≤ 0.15) manganites.

Abstract

La0.8Na0.2-x □ x MnO3 (0.00 ≤ x ≤ 0.15) manganites were successfully synthesized using the solid-state route. X-ray diffraction was performed to check the samples' purity and phase structure. Scanning electron microscopy analysis reveals a decrease in the average grain size with an increase in the deficiency amount. Analysis of the temperature dependence of magnetization proved the presence of ferromagnetic-paramagnetic transition in all the studied samples. The magnetization derivative (d2 M/dT 2) curves demonstrated a decrease in the transition temperature with an increase in the deficiency amount. Such experimental observations can be correlated with bandwidth evolution, which affected double-exchange interactions. It can be equally accounted for by the average grain size decrease. In this regard, the experimental measurements of effective paramagnetic moments revealed the existence of ferromagnetic correlations within the paramagnetic phase. Notably, different electrical findings were addressed. Indeed, the frequency dependence of electrical conductivity displayed the coexistence of two frequency slopes reflecting the presence of Jonscher's double power law for all the studied samples. A significant decrease in conductivity values was observed when the deficiency amount increased. This experimental observation could be assigned to the decrease in the grain size (conductor region). Such assumption was confirmed by the evolution of the grain boundary resistance with deficiency level. Indeed, a significant mounting in the grain boundary resistance values was obtained presenting the increase of the resistive region for x = 0.15. It is worth noting that the Curie temperature for the x = 0.10 sample was found to be close to room temperature (T C = 297 K). These findings make the La0.8Na0.1□0.1MnO3 compound a powerful candidate for many technological applications.