The role of oxygen plasma in modification of surface microstructure and electrical transport properties of La_0.7Ca_0.3MnO₃ ceramics

Perovskite manganites have attracted great attention owing to their remarkable combination of electrical, magnetic, and structural tunability, making them suitable for a variety of functional devices. In this study, the influence of oxygen plasma exposure on the structural and electrical properties of bulk La_0.7Ca_0.3MnO₃ (LCMO) manganite was examined for exposure durations of 5 and 10 min. X-ray diffraction patterns of pristine and plasma-treated samples were refined using the Rietveld method with the orthorhombic Pnma structure as reference, yielding good fits (χ2 < 2). The lattice parameters and Mn-O bond lengths increase gradually with increasing plasma exposure time, while the Mn-O-Mn bond angles remain nearly unchanged. This structural evolution is accompanied by an increase in the unit cell volume, suggesting an overall expansion of the lattice, which is attributed to the incorporation of oxygen species during plasma treatment. X-ray photoelectron spectroscopy analysis confirmed an increase in the Mn4+/Mn3+ ratio, indicating oxygen enrichment in the lattice. Pristine LCMO exhibit a characteristic metal-insulator transition at temperature T_p ∼100 K. With increasing plasma exposure duration, a decrease in resistivity peak and a slight shift of T_p towards higher temperature are observed, indicating enhanced metallic behavior. The improved conductivity due to oxygen plasma exposure is explained using double exchange mechanism, Jahn-Teller distortion and phenomenological percolation model.