Nuclear Instruments and Methods in Physics Research A 575 (2007) 176–179 XAFS and neutron diffraction study of La 1x Sr x Co 1y Nb y O 3 V.V. Efimov a,Ã , E. Efimova a , D. Karpinsky b , D.I. Kochubey c , V. Kriventsov c , A. Kuzmin d , S. Molodtsov e , V. Sikolenko a,f , J. Purans g , S. Tiutiunnikov a , I.O. Troyanchuk b , A.N. Shmakov c , D. Vyalikh e a Joint Institute for Nuclear Research, Joliot-Curie 6, Dubna 141980, Moscow Region, Russia b Institute of Solid State and Semiconductor Physics, 220072 Minsk, Belarus c Boreskov Institute of Catalysis, Lavrentiev prosp. 5, Novosibirsk 630090, Russia d Institute of Solid State Physics, Kengaraga Str. 8, LV-1063 Riga, Latvia e Institut fu ¨r Kristallographie und Festko¨rperphysik (IKFP), Zellescher Weg 16, Physikgeba ¨ ude C 115, 01069 Dresden, Germany f Hahn-Meitner-Institut Glienicker Str. 100, Berlin D-14109, Germany g Dipartimento di Fisica, Universita’di Trento, Via Sommarive 14, I-38050 Povo (Trento), Italy Available online 21 January 2007 Abstract The effect of hole doping on the crystal and electronic structure of La 1x Sr x Co 1y Nb y O 3 (y ¼ 0.0–0.25) at the x ¼ 0.0; 0.2; 0.5 has been studied by neutron diffraction and X-ray absorption spectroscopy at the Co K and L 2,3 -edges. The preliminary analysis of the Co K and L 2,3 -edges X-ray absorption near edge structure (XANES) in La 1x Sr x Co 1y Nb y O 3 series suggests that upon niobium doping, an increase of the intermediate Co 3+ spin state and a decrease of low spin Co 4+ states contributions occur. The possible explanation of the observed changes of crystal and electronic structure in these cobaltites is discussed. r 2007 Elsevier B.V. All rights reserved. PACS: 61.10.Ht; 61.12.Ld; 71.70.Ej; 75.25.+z; 75.30.Et; 76.30.Kg Keywords: XAFS; X-ray and neutron diffraction; Cobaltites 1. Introduction In LnCoO 3 oxides (Lnlanthanide), Co ions in the ground state are characterized by the low-spin electronic configuration t 6 2g e 0 g . This state (LS; S ¼ 0) gradually passes to intermediate spin one (IS; S ¼ 1; t 5 2g e 1 g ) with temperature enhancement [1]. For example, the spin state of cobalt ions in LaCoO 3 gradually changes from LS to IS with temperature increment in the temperature range of 40–100 K. In the case of La 1x Sr x CoO 3 , the Sr 2+ ionic radius is significantly greater than that of the La 3+ ion; so it is possible to expect stabilization of the intermediate spin state of cobalt ions by substituting Sr 2+ ions for La 3+ ones [2]. However, at such heterovalent substitution low spin Co 4+ ions appear [3], leading to the ferromagnetic metallic ground state [4]. The majority of researchers suppose that ferromagnetism in cobaltites is caused by ‘‘a double exchange’’, as in manganites. To prevent the Co 4+ ion appearance, it is possible to introduce simultaneously Nb 5+ ions, which at the presence of Co 3+ ions will be in oxidizing state 5+. By simultaneously introducing Sr 2+ and Nb 5+ , the cobalt ions keep their valence state, and the electroconductivity of La 1x Sr x Co 1y Nb y O 3 solid solu- tions decreases with dopant concentration enhancement. Thus, the different nature of ferromagnetic interactions formation in the given systems is observed [5]. In the case of La 1x Sr x Co 1x/2 Nb x/2 O 3 , the ferromag- netic component can be caused only by cobalt ions inside crystallites, as the average grain size is about 10 mm. We suppose that strontium ions, which have an ionic radius much larger than that of lanthanum ones, increase the mean Co–O distance in some CoO 6 octahedra, which favors the Co 3+ ion transition from LS to IS state. Thus, ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2007.01.061 Ã Corresponding author. Tel.: +7 049621 64 173; fax: +7 49621 65 767. E-mail address: efimov@sunse.jinr.ru (V.V. Efimov).