Speaker
Prof.
Yuri Mikhlin
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of sciences)
Description
Chalcopyrite CuFeS2, is the most common mineral of copper; chalcopyrite and related compounds are of interest for thermoelectric, photovoltaic and other applications. We also examined valleriite (Fe,Cu)S(Mg,Al)(OH)2, natural nanocomposite composed of chalcopyrite-like Fe,Cu sulfide layers and brucite-like oxide layers, which is important mineral of Norilsk ore deposits. Conventional XPS and synchrotron-based hard photoemission spectroscopy (HAXPES), surface-sensitive Cu L-, Fe L-, S L-edge TEY XANES and S K-, Fe K-edge TEY and PFY XANES spectroscopy were used along with some other experimental techniques and DFT+U calculations in order to characterize near-surface regions of the initial (in fact, oxidized in air) minerals and the ones chemically oxidized in Fe(III) solutions. The synchrotron irradiation experiments were performed at Russian-German laboratory and HIKE endstations at BESSY II facility (Helmholtz Zentrum Berlin). Both the element concentrations and the chemical state of atoms, e.g., mono-, di-, polysulfide and other S species, as a function of the probing depth and the reaction conditions, were studied. The near-surface regions of chalcopyrite are generally consist of (i) a thin, no more than 1-4 nm, strongly metal-depleted outer layer containing polysulfide species, (ii) a layer with smaller stoichiometry deviations and low, if any, concentrations of polysulfide, which composition and dimensions strongly depend on the chemical treatment conditions, and (iii) an about stoichiometric underlayer extended to at least several dozen of nanometers. The latter shows Fe K-edge TEY spectra altered probably due to a high content of defects, even if only oxidized in ambient air. In contrast to other spectra, Cu L-XANES patterns were surprisingly insensitive to the changes of the composition of the reacted near-surface layers. DFT+U analysis of the iron-deficient structures formed shows that polysulfide species are stable only near the surface, copper remains 4-fold coordinated to S in the layers with disulfide anions, the layer with iron deficiency transforms from antiferromagnetic and semiconducting state into paramagnetic metallic state. Moreover, the formation of these structures is generally energy-favorable under the oxidative conditions. The lengthy regions are expected to heavily affect the electronic characteristics and processes involving surface and interfacial charge transfer.
Primary author
Prof.
Yuri Mikhlin
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of sciences)
Co-authors
Dr
Alexander Romanchenko
(Institute of Chemistry and Chemical Technology of SB RAS)
Dr
Sergey Vorobyev
(Institute of Chemistry and Chemical Technology of SB RAS)
Mr
Valentin Shurupov
(Institute of Chemistry and Chemical Technology of SB RAS)
Dr
Vladimir Nasluzov
(Institute of Chemistry and Chemical Technology of SB RAS)
Dr
Yevgeny Tomashevich
(Institute of Chemistry and Chemical Technology of SB RAS)
