Synthesis and characterisation of La 12x MnO 3^d nanopowders prepared by acrylamide polymerisation G. Dezanneau a, * , A. Sin b , H. Roussel a , H. Vincent a , M. Audier a a Laboratoire des Mate Âriaux et du Ge Ânie Physique, BP46, domaine universitaire, 38402 Saint Martin d'He Áres cedex, France b Pirelli Cavi e Sistemi S.p.A., Viale Sarca 222, 20126 Milano, Italy Received 5 July 2001; accepted 31 October 2001 by C. N. R. Rao Abstract La 12x MnO 3^d x  20.02 to 0.35) nanocrystalline powders were prepared by a new sol±gel method. It is used the acryl- amide geli®cation 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 ®ne 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 La 0.9 MnO 3 and Mn 3 O 4 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-de®cient La 0.94 Mn 0.92 O 3 compound. q 2002 Elsevier Science Ltd. All rights reserved. PACS: 75.50.Pa; 73.61.Tm; 75.50.Kj; 81.20.Fw Keywords: manganite; sol±gel synthesis; vacancies; low temperature 1. Introduction The renewed interest in lanthanum manganites and their solid solutions was induced by the discovery of colossal magnetoresistance effect CMR) effect in 1993[1,2]. The majority of works was devoted to rare earth manganites doped with alkaline-earth elements corresponding to the general formula La 12x A x MnO 3^d A  Ca, Ba, Sr). Sur- prisingly, less studies have been performed on vacancy doped manganites La 12x MnO 3^d while they also present considerable interest from the point of view of potential applications as well as fundamental problems of compo- sition-structure-properties correlation. The most complete data are available for compounds with a La/Mn ratio equal to one and variable oxygen content[3±7]. All these studies show that the excess of oxygen, re¯ected by the general formula LaMnO 31d , should be better understood by con- sidering cation vacancies rather than interstitial oxygen anions. This excess of oxygen d strongly depends on syn- thesis and thermal treatment conditions, the higher values of d being obtained at low temperature and highly oxidative atmosphere. On the other hand, the more general series of compounds La 12x MnO 3^d x  0 to 0.3) have also been studied but with very disparate results concerning structural and magnetic properties [8±11]. These compounds when obtained under oxidative atmosphere are generally rhombo- hedral R-3c space group) and present ferromagnetic proper- ties, with a maximum Curie temperature reported of 280 K [11]. The phase diagram of such a series of composition has been studied in details by Van Roosmalen et al. [12] who showed that for La/Mn , 0.9, a demixion should occur between a lanthanum manganite phase and a manganese Solid State Communications 121 2002) 133±137 0038-1098/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0038-109801)00461-6 PERGAMON www.elsevier.com/locate/ssc * Corresponding author. Tel.: 133-4-76-82-63-29; fax: 133-4- 76-82-63-94. E-mail address: gdezano@inpg.fr G. Dezanneau).