Metallic and semi-conducting resistivity behaviour of La0.7Ca0.32xKxMnO3 (x 5 0.05, 0.1) manganites

The temperature dependence of electricalresistivity, p, of ceramic La(0.7)Ca(0.3-x)K(x)MnO(3) (x = 0.05,0.1) is investigated in metallic and semi-conducting phase.The metallic resistivity is attributed to be caused by electron–phonon, electron–electron and electron–magnonscattering. Substitutions affect average mass and ionic radiiof A–site resulting in an increase in Debye temperature hDattributed to hardening of lattice with K doping. Theoptical phonon modes shift gradually to lower mode frequenciesleading to phonon softening. Estimated resistivitycompared with reported metallic resistivity, accordinglyand..., infers electron–electron and electron–magnon dependence over mostof the temperature range. Semi-conducting nature is discussedwith variable range hopping and small polaronconduction model. The decrease in activation energies andincrease in density of states at the Fermi level withenhanced Ca doping is consistently explained by cationicdisorder and Mn valence.