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XANES and EXAFS characterization of (111) oriented NiCo2O4 Thin films grown by ion beam sputtering

AuthorsPrieto, Pilar ; Ruiz-Gómez, Sandra; Marco, José F.; Serrano Rubio, Aída ; Aballe, L.; de la Figuera, Juan
Issue Date26-Jun-2019
CitationX Iberian Conference on Tribology / XI Iberian Vacuum Conference (2019)
AbstractBimetallic oxide NiCo2O4 (NCO) is an infrared transparent conductor with a resistivity orders of magnitude lower than the spinel Co3O4 or Ni itself, which is also ferrimagnetic. In nanostructured form, it is an emerging material for supercapacitors in energy storage applications that require high specific power, fast charge-discharge times and a lon cycle life [1, 2]. In thin film form, spintronic applications due to the coexistence of ferromagnetic order, metallic transport and infrared transparency are being explored. The large magnetoresistance reported on (100) NiCo2O4 epitaxial films, attributed to a nanoscale phase separation in which a ferrimagnetic metallic spinel phase and an insulating ferrimagnetic rocksalt phase coexist [3, 4], can be explain by spin-filtering effect across the insulating phase. The fundamental properties on spinel ferrites depend on both the cation oxidations states [5] and the cation interstitial site distribution. Therefore their determination is basic to understanding those properties and to find the mechanisms to tailor its properties. Nominally, NCO is an inverse spinel with its formula written as [Co¿2+Co1-¿3+] A [Co3+Ni1-¿2+Ni¿3+]BO42- where the tetrahedral A-site are occupied with high spin Co2+ and Co3+ while the octahedral B site are occupied by Ni2+, low spin Ni3+ and low spin Co3+ cations. One intriguing property of NCO is the possibility of changing the spin state of its cations. The 3d degeneracy of Ni and Co breaks down due to the crystal field of the surrounding oxygen anions, splitting them into two sets. Depending on the crystal field splitting and the particular valence, a particular cation can be in either a high-spin or low-spin configuration. In this work, we grow high quality (111) oriented films of NCO on Al2O3(0001) substrates by ion beam sputtering (IBS). This method allows to control the energy deposited per atom and provides excellent properties of the films grown. The films have been characterized by XANES and EXAFS in addition to XRD, four point-resistivity measurements, and XPS. References [1] M-C. Liu et al., A Sol-Gel Process for the Synthesis of NiCo2O4 Having Improved Specific Capacitance and Cycle Stability for Electrochemical Capacitors, Journal of The Electrochemical Society 159 (2012) A1262. [2] J. Chang et al., Template-free approach to synthesize hierarchical porous nickel cobalt oxides for supercapacitors, Nanoscale 4 (2012) 6786. [3] Peng Li et al., Spin Filtering in Epitaxial Spinel Films with Nanoscale Phase Separation, ACS Nano 11 (2017) 5011. [4] H. Sharona et al., Coexisting nanoscale inverse spinel and rock salt crystallographic phases in NiCo2O4 epitaxial thin films grown by pulsed laser deposition, Journal of Applied Physics 122 (2017) 225301. [5] J.F. Marco et al., Cation distribution and magnetic structure of the ferrimagnetic spinel NiCo2O4 Journal of Materials Chemistry 11 (2011) 3087.
DescriptionIBERTRIVA 2019 X Iberian Conference on Tribology – IBERTRIB, XI Iberian Vacuum Conference - RIVA, Seville, Spain,June 26-28
Appears in Collections:(ICV) Comunicaciones congresos
(IQFR) Comunicaciones congresos
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