Jahn-Teller distortion induced by Mg/Zn substitution on Mn sites in the perovskite manganites

The effect of Mg doping in La2/3Sr1/3Mn1-xMgxO3 (0.05 less than or equal to x less than or equal to 0.2) and Zn doping in LaMn1-yZnyO3 (0.05 less than or equal to y less than or equal to 0.4) were investigated. For heavily doped samples with x greater than or equal to 0.15 and with y greater than or equal to 0.10, there are not the insulating-metallic transition associated with the paramagnetic-ferromagnetic transition. It is suggested that the MnO6 octahedron neighboring Mg/Zn is contorted by Mg/Zn doping and the Jahn-Teller (JT) distortion of the Mn3+ ion in contorted MnO6 octahedron is different from that in conventional MnO6 octahedron. The eg carriers must overcome the energy gap caused by different JT distortion. This is the origin of insulating behavior in ferromagnetic state. This view can be proved by fitting XRD data and IR spectra. The conductive behavior is determined by thermal activation model. (C) 2003 Elsevier B.V. All rights reserved.