Synthesis and characterisation of La1-xMnO3±δ nanopowders prepared by acrylamide polymerisation

La1-xMnO3+b (x = -0.02 to 0.35) nanocrystalline powders were prepared by anew sol-gel method. It is used the acryl-amide gelification to form an organic 3D tangled network where a solution of the respective cations is soaked. This method was adapted to cover a broad range of high impact electro-ceramic oxides, which a particular example is the CMR nanopowders reported in this work. The acrylamide sol-gel process is a fast, cheaper and easy to scale-up method for obtaining fine powders of complex oxides. This synthesis method allows performing 100 g of highly pure nanopowders in one run with simple laboratory scale, The sponge like powder obtained consists of thin sheets composed of nanocrystallites whose size varies from 66 nm to 30 nm, depending on composition. The oxygen content of the manganite powder is shown to decrease with vacancy-doping on lanthanum site. Such a evolution can be explained for La/Mn <0.9 by considering a demixtion of the powder into La0.9MnO3 and Mn3O4 phases, while for La/Mn >0.9, the high oxygen excess leads to consider vacancies on both lanthanum and manganese sites. Both hypotheses are supported by magnetic measurements, which show a constant Curie temperature of 295 K for La/Mn <0.9, while for La/Mn >0.9, the occurrence of vacancies on manganese sites progressively impedes the ferromagnetic interactions, leading to a cluster-glass behaviour in the case of the highly manganese-deficient La0.94Mn0.92O3 compound. (C) 2002 Elsevier Science Ltd. All rights reserved.