First-principle calculations analysis of ELNES splitting for Mn 3 O 4 spinels related to atomic local symmetry Po-Tuan Chen a , Chuan-Ming Tseng a,b , Tung-Yuan Yung c , Ming-Wen Chu a , Cheng-Hsuan Chen a , Michitoshi Hayashi a,n a Center for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan b Institute of Physics, Academia Sinica, Taipei 115, Taiwan c Institute of Nuclear Energy Research, Atomic Energy Council, Executive Yuan, Longtan, Taoyuan 32546, Taiwan article info Article history: Received 4 October 2013 Received in revised form 14 January 2014 Accepted 18 February 2014 Available online 6 March 2014 Keywords: ELNES Mn 3 O 4 Jahn–Teller effect FEFF abstract By using a real space multiple scattering method (FEFF code) with a 2  2  2 cluster model, we investigated the effects of characteristic Jahn–Teller distortion on the electron energy loss near-edge structure (ELNES) of Mn 3 O 4 spinel. In particular, we examined a correlation between the characteristics of the density of state and the ELNES spectral feature as a function of Jahn–Teller distortion. To this end, we introduced a geometrical variation approach to an Mn 3 O 4 cluster model containing both Mn 3 þ and Mn 2 þ sites. Upon a prominent Jahn–Teller distortion of the Mn 3 þ -octahedral site, we resolved the associated spectral features of Mn, comprising three peaks that merged upon increasing the symmetry of octahedral site from tetragonal (D 4h ) to cubic (O h ). We have also investigated the interplay between the Mn L-edge and corresponding O K-edge spectra. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Manganese oxide spinels are used in many industrial applica- tions, including photodecomposition [1], ion exchange [2], mole- cular absorption [3], supercapacitors [4], magnetic utilization [5], and batteries [6]. A spinel has the general formula AB 2 O 4 , where A and B are metal cations in the nominal oxidation states of þ 2 and þ 3, respectively. In a normal spinel (Fig. 1), the octahedral sites are occupied by B 3 þ ions while the tetrahedral sites are occupied by A 2 þ ions. The so-called Jahn–Teller effect explains the relationship between a spinel's geometric symmetry and its electronic configuration in various oxidation states. Several spec- tral investigations have been undertaken to experimentally probe the Jahn–Teller splitting energy in Mn-containing spinels [7,8]. Manganese atoms at B 3 þ sites can induce Jahn–Teller distortion, decreasing the local symmetry of the octahedron from O h to D 4h . This distortion may give rise to splitting of the signals in the spectra of the spinel. Electron energy loss spectroscopy (EELS) is used widely to investigate the electronic structures of materials; in particular, their electron energy loss near-edge structures (ELNESs; i.e., the intensity variations within approximately 10 eV of the edge threshold) that arise as a result of electronic perturbations of the energy level distribution and environment of the atom being excited. Characteristic features of ELNES, such as the oxygen K-edge and the transition metal L-edge, are commonly used as fingerprints of the oxidation state [9], the coordination of specific ions in 3d metal oxides structures [10], and the local structural environments for atoms in a crystal [11]. The spectral features are practically equivalent to the near-edge fine structures observed in X-ray absorption spectroscopy (XANES); they are of appreciable academic interest because of the rich chemical and physical information contained. As an industrially significant example, mixed-valence Mn 3 O 4 is constituted by Mn 2 þ species at the A sites (thus, Mn A 2 þ ) and Mn 3 þ species at the B sites (Mn B 3 þ ) [12]. The site-specific model has been used to interpret ELNES spectra of Mn 3 O 4 ; it can be employed to demonstrate how these two sites contribute to ELNES spectra. Tatsumi et al. [13] have proposed that Mn B contributes to the higher energy region than Mn A due to the more ionic character of the octahedral site. In addition, using electron energy loss spectro- scopy in conjunction with scanning transmission electron micro- scopy (STEM-EELS), Tan et al. [14] have proposed that the Mn L 3 -edge in the ELNES spectrum comprises two peaks from different A and B sites, respectively. Several comparisons of the experimen- tally measured Mn L 2,3 - edges of the respective Mn A 2 þ and Mn B 3 þ Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ultramic Ultramicroscopy http://dx.doi.org/10.1016/j.ultramic.2014.02.002 0304-3991 & 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ886 2 33665250. E-mail address: atmyh@ntu.edu.tw (M. Hayashi). Ultramicroscopy 140 (2014) 51–56