Preparation of manganite perovskites by a wet-chemical method involving a redox reaction and their characterisation

Manganite perovskites compounds are prepared through a wet-chemical techniq ue. Here the hydrated MnO2 is precipitated first from Mn(VII) and Mn(II) sa lts using a redox reaction in nitric acid medium. Hydrated MnO2 is black in colour, has large porosity and high surface area > 120 m(2)/g and acts as a precursor for the preparation of manganite perovskites. Thermogravimetric studies show that the MnO2 phase changes to Mn2O3 upon heating to 783 K. V arious perovskite compounds have been prepared, all compositions exhibit hi gh concentration of Mn4+ ions. Transmission electron microscopy showed the presence of well-facted crystallites of Ca-, Ba-substituted LaMnO3 and thei r size ranges from 100 to 400 nm. Resistivity, thermopower and magnetoresis tance studies are carried out for the composition La(0.667)Cao(0.333)MnO(3) which displayed a large magnetoresistance coefficient (similar to 0.8) in a magnetic field of 1 T. (C) 2000 Elsevier Science S.A. All rights reserved .