Metallic and semi-conducting resistivity behaviour of La0.7Ca0.3âxKxMnO3 (x = 0.05, 0.1) manganites

Abstract

AbstractThe temperature dependence of electrical resistivity, Ï, of ceramic La0.7Ca0.3âxKxMnO3 (x = 0.05, 0.1) is investigated in metallic and semi-conducting phase. The metallic resistivity is attributed to be caused by electronâphonon, electronâelectron and electronâmagnon scattering. Substitutions affect average mass and ionic radii of Aâsite resulting in an increase in Debye temperature θD attributed to hardening of lattice with K doping. The optical phonon modes shift gradually to lower mode frequencies leading to phonon softening. Estimated resistivity compared with reported metallic resistivity, accordingly Ïdiff. = [Ïexp. â {Ï0 + Ïeâph (=Ïac + Ïop)}], infers electronâelectron and electronâmagnon dependence over most of the temperature range. Semi-conducting nature is discussed with variable range hopping and small polaron conduction model. The decrease in activation energies and increase in density of states at the Fermi level with enhanced Ca doping is consistently explained by cationic disorder and Mn valence.