G. Carabali 1 , J. Jiménez-Mier 1 , Olalde . P, E. Chavira 2 , W. Yang 3 , E. Bucio 1

1. Novel sol-gel methodology to produce nano-materials using gamma irradiation Preliminary results of the electronic structure of La1-xSrxCoO3 compound by XAS G. Carabali1, J. Jiménez-Mier1, Olalde. P, E. Chavira2, W. Yang3, E. Bucio1 1 Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, 04510 México D. F., México. 2Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, 04510 México D. F., México. The Advanced Light Source, Lawrence Berkeley NationalLaboratory, Berkeley, California 94720, USA E-mail: gealcasa@gmail.com • INTRODUCTION • Mixed oxide-based-materials with the perovskite structure ABO3 have been investigated for both fundamental and technological reasons. This kind of materials has a variety of properties that make them useful in different applications. For example, Lanthanum cobalt oxide (LaCoO3) has attracted much attention because it shows fascinating changes in the electronic and magnetic properties as a function of temperature and/or divalent substitution. The undoped compound LaCoO3 has a rhombohedrally distorted perovskite structure and exhibits a semiconducting behavior below room temperature. Its ground state is known to be low-spin nonmagnetic Co3+ (S=0, t62g). Substituting La3+ with Sr2+ decreases the rhombohedral distortion and introduce ferromagnetic long range order with a metal-like behavior in the whole temperature range [1,2]. • In this poster, we present preliminary results of absorption and emission of X-ray spectroscopy studies on La1-xSrxCoO3 (x= 0.0, 0.15, 0.3 and 0.5) with the aim of understanding the effect of Sr doping in the electronic structure. 2. DIAGRAM OF POLIMIMERIC SOL-GEL REACTION O Acryl-amide chains La Gel formation (chains crosslinked ) Chelated metal Cations 6oCo Co Dry process of gel ABO3 Heat process Heat process 500 °C γ-radiation Heat process 200 °C Final Product Fig.1. Diagram of polymeric sol-gel reaction. Chelating agent Fig. 3. Tanabe sugano diagram The Tanabe-Sugano diagram shows the energy levels as a function of the crystal field- splitting parameter (10Dq) for the 3d6 configuration. 3. PRELIMINARY RESULTS OF ELECTRONIC STRUCTURE b Scheme of synchrotron machine The superposition of the electronic states with different symmetries (A1, A2, E, T1, and T2) a Fig. 2. a) Schematic illustration of : a) synchrotron machine. b) the experimental setup at Beamline 8.0.1. of Advance Light Sources in Berkeley. c) absorption and emission process [1]. c In x-ray absorption spectroscopy (XAS) in the region of the transition metal L edge a 2p electron is excited into an unoccupied (conduction) state. It therefore gives information about excited 3d states of the cobalt ion. Calculation is in accordance with Hund's rule: for low values ​​of the 10 Dq parameter; the ground state is in high spin. Fig. 4. X-ray absorption spectra (XAS) of La1-xSrxCoO3 compound (x= 0.0, 0.15, 0.3 and 0.5)at oxygen K-edge. Replacing La3+ with Sr2+ induces states within the band gap of the insulating undoped compound and these doped states have a very substantial oxygen 2p character. This could be an indication that the insulating compounds belong to the charge transfer insulator regime. Fig. 3. Co 2p X-ray absorption spectra of La1-xSrxCoO3 compound. The red symbol line represent experimental spectra and black line correspond to the calculated spectra with the crystal field multiplet calculations that take into account transfer charge effects. Table 1. Parameters used in multiplet calculation Conclusions: The preliminary results presented in this work indicate that strontium-doping at LaCoO3 perovskite produces a reduction in the 10 Dq parameter and generates new states near the Fermi level. X-ray absorption and spectroscopies provide very useful information about the electronic structure of emission transition metal compounds. One can clearly establish differences in the spectra due to different chemical environments. Bibliography: [1] T. Saitoh, T. Mizokawa, A. Fujimori, M. Abbate, Y. Takeda, and M. Takano,Phys. Rev. B 55 (1997) 4257 [2] O. Toulemonde, N. N’Guyen, F. Studer, J. SolidStateChem. 158 (2001) 208–217. [3]S.M. Butorin, J. ElectronSpectrosc. Relat. Phenom10–111 (2000) 213–233 WorksupportedbyCONACyTunderproject 56764 The shoulders in L3 indicated by the arrows in figure 3, is the main feature in this comparison of Co 2p absorption spectra. It move toward lower energy values as strontium is introduced in the compound., indicating a change from a low-spin to a high-spin ground state.