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

摘要

Manganite perovskites compounds are prepared through a wet-chemical technique. Here the hydrated MnO2 is precipitated first from Mn(VII) and Mn(II) salts 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. Various perovskite compounds have been prepared, all compositions exhibit high concentration of Mn4+ ions. Transmission electron microscopy showed the presence of well-facted crystallites of Ca-, Ba-substituted LaMnO3 and their size ranges from 100 to 400 nm. Resistivity, thermopower and magnetoresistance 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. References: 15