P 75 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
LOCAL ELECTRONIC STRUCTURE AND PHYSICAL PROPERTIES OF Zn
1−xNi
xCr
2Se
4P. Zajdel1∗, I. Jendrzejewska2, J. Goraus1, T. Goryczka3, and T. Mydlarz4
1Institute of Physics, University of Silesia, ul. Uniwersytecka 4, 40–007 Katowice, Poland
2Institute of Chemistry, University of Silesia, ul. Szkolna 9, 40–006 Katowice, Poland
3Institute of Chemistry and Physics of Metals, University of Silesia, ul. Bankowa 12, 40–006 Katowice, Poland
4International Laboratory of High Magnetic Fields and Low Temperatures, ul. Gajowicka 95, 53–529 Wroc law, Poland
Keywords: spinels, XAS
∗e-mail : pawel.zajdel@us.edu.pl
We have performed X-Ray Absorption studies of nickel doped ZnCr2Se4 in order to elucidate the influence of Ni on the structural and electronic prop- erties of the system.
Upon doping the structure is preserved up to x = 0.3, where traces of monoclinic phase start to appear. Lattice parameters of the spinel phase decrease with increased nickel content, which is in agreement with smaller crystal and ionic radii of Ni+2 (69 pm, 55 pm) vs Zn+2(73 pm, 60 pm) (Fig- ure 1).
Figure 1 : Lattice parameter of Zn1−xNixCr2Se4.
For further study we have concentrated on single phase compounds with highest nominal nickel con- tent x = 0.2. The chemical composition was verified with ICP-AES method to be Zn0.79Ni0.18Cr2.18Se4
and independently from the Rietveld refinement Zn0.811(7)Ni0.230(8)Cr0.970(6)Se4.
The principal question is the local structure and nominal oxidation state of nickel. In order to anal- yse it, we have performed room temperature X-Ray Absorption Spectroscopy (XAS) studies on Cr K,
Ni K and Se K edges of the compounds. The ex- periments were performed on stations 7.1 and 9.3 of the Daresbury SRS.
The analysis of the near edge (XANES) region of Ni K edge (Figure 2.) revealed that it slightly shifts to higher energies with increases Ni content.
Its oxidation state is similar to nickel in NiCr2Se4, nominally Ni+2.
To corroborate this result we have performed Full Potential – Linear Orbital calculations of the band and electronic structure of Zn0.8Ni0.2Cr2Se4. The calculated densities of states (DOS) gave a good agreement with the experimental absorption edges similar as in the case of octahedrally coordinated Ni [1].
Figure 2 : Room temperature XANES spectra of doped Zn1−xNixCr2Se4.
References
[1] I. Jendrzejewska, P. Zajdel, T. Goryczka, J. Goraus, A. Kita, T. Mydlarz, J. Alloy. Comp. 520 (2012) 153 – 157.
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