Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu 1+Fe3+S2 2-. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods. © 2014 Pleiades Publishing, Ltd

NQR/NMR and Mössbauer spectroscopy of sulfides: Potential and versatility

Nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and nuclear gamma-resonance (NGR or Mössbauer Effect) methods are generally described as highly sensitive tools in studies of local electronic structure and symmetry in solid-state materials. This is due to high informativity in electronic structure investigations, high resolution in phase-structural diagnostics (down to nano-scale), possibility to study polycrystalline and complex compounds, and to the non-destructive character of these methods. As applied to Earth sciences, both NQR/NMR and Mössbauer spectroscopy methods contribute to mineralogical material science and mineral physics. Another important aspect is the fact that these methods, as demonstrated recently, belong to unique techniques suitable for on-line bulk mineralogical analysis. This includes remotely operated sensors used with conveyor systems in mining/materials handling and similar applications where real-time data collection/processing provides significant commercial benefits. These developments open new pathways for NQR/NMR and Mössbauer spectroscopy applications. Notably, NQR/NMR and Mössbauer effects are observed primarily on different nuclei-probes but provide similar information about the local properties of materials (hyperfine fields, electric field gradients and relaxation effects). This makes NQR/NMR and Mössbauer methods mutually complementary despite their significant technical differences. This paper includes examples of recent applications of NQR, NMR and Mössbauer spectroscopic tools to studies of copper-, antimony- and iron-containing sulfides, demonstrating how these methods can contribute to an improved understanding of geochemical problems. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart

Application of 57Fe Mössbauer spectroscopy as a tool for mining exploration of bornite (Cu5FeS4) copper ore

Nuclear resonance methods, including Mössbauer spectroscopy, are considered as unique techniques suitable for remote on-line mineralogical analysis. The employment of these methods provides potentially significant commercial benefits for mining industry. As applied to copper sulfide ores, Mössbauer spectroscopy method is suitable for the analysis noted. Bornite (formally Cu5FeS4) is a significant part of copper ore and identification of its properties is important for economic exploitation of commercial copper ore deposits. A series of natural bornite samples was studied by 57Fe Mössbauer spectroscopy. Two aspects were considered: reexamination of 57Fe Mössbauer properties of natural bornite samples and their stability irrespective of origin and potential use of miniaturized Mössbauer spectrometers MIMOS II for in-situ bornite identification. The results obtained show a number of potential benefits of introducing the available portative Mössbauer equipment into the mining industry for express mineralogical analysis. In addition, results of some preliminary 63,65Cu nuclear quadrupole resonance (NQR) studies of bornite are reported and their merits with Mössbauer techniques for bornite detection discussed

Oxidation and magnetic states of chalcopyrite CuFeS2: a first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X ray photoemission, X ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu1+Fe3+S. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods

Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu 1+Fe3+S2 2-. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods. © 2014 Pleiades Publishing, Ltd

Security informed safety assessment of industrial FPGA-based systems

The strong interconnection and interrelation of safety and security properties of industrial system which are based on programmable logic (field programmable gate arrays, FPGA) is reviewed. Information security, i.e. system's ability to protect the information and data from unauthorized access and modification, is a subordinate property with respect to safety of many instrumentation and control systems (I&Cs), primarily to the NPP reactor trip systems. Such subordination may be taken into account by implementation of security informed safety (SIS) approach. The methodology for safety assessment of FPGA-based systems which are widely used in industrial critical systems is described. It is based on joint using of security analysis techniques (GAP-analysis and intrusion modes, effects and criticality IMECA analysis) and also their reflection on the final safety assessment picture of the system with two channels. This methodology forms so called security informed safety approach. Additional aspects of safety assessment of diverse instrumentation and control FPGA-based systems for safety-critical application are described

Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu 1+Fe3+S2 2-. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods. © 2014 Pleiades Publishing, Ltd

Oxidation and magnetic states of chalcopyrite CuFeS2: A first principles calculation

The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu 1+Fe3+S2 2-. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the valence state can be confirmed experimentally by nuclear magnetic and nuclear quadrupole resonance and Mössbauer spectroscopy methods. © 2014 Pleiades Publishing, Ltd

Low-temperature magnetic properties of chalcopyrite (CuFeS2) studied by 63,65Cu-NMR and 57Fe-Mössbauer spectroscopy

Chalcogenide minerals exhibit a fascinating variety of crystal-chemistry and physical properties that is of both scientific interest and potential practical application value. The role of ternary chalcogenide CuFeS2 (referred to as chalcopyrite) should be specially emphasized. On the one hand, chalcopyrite is known as a very important commercial source of copper ore. On the other hand, chalcopyrite-based chalcogenide group of minerals is considered as a perspective generation of solar cells. This is due to their high optical absorption coefficient when compared with known materials, with their energy band gap varied within the range of 0.8-3.5 eV by controlling chemical composition. This is also the reason for these materials finding wider application in optoelectronic devices. From scientific point of view, CuFeS2 has drawn strong interest as an antiferromagnetic semiconductor. One of known specific features of CuFeS2 is the occurrence of polymer-like structure consisting of –Cu–S–Fe– chains. This structure leads to the presence of several unusual properties of electronic and magnetic origin. Particularly, the values of Fe magnetic moments in CuFeS2 with 3.85μB are significantly less than those for the magnetic trivalent Fe, necessitating considerations of valence states of iron and copper ions [1]. Unusual behavior of electrical resistivity of chalcopyrite leads to the discussions about the nature of its electronic type (for example, zero-gap semiconductor [2] or unusual insulator of Haldane–Anderson type [3]). Neutron diffraction examination reveals phase transition in CuFeS2 at 50K temperature [4], however earlier Mössbauer studies provide no evidence of such behavior [5].Thus, clarification of the points mentioned above requires comprehensive study of local properties of CuFeS2 and local methods providing experimental information at micro- and nano-scale are most suitable for this purpose. In addition, combination of different local methods appears to be more expedient in complex studies due to the possibility of observing and comparing electron-nuclear interactions using different nuclei probes [6]. Joint application of nuclear resonance spectroscopic methods (Mössbauer Effect and NMR, NMR and NQR, Mössbauer Effect and ENDOR and other) are some of the examples of such joint experimental techniques. In this report, we present some preliminary results of chalcopyrite studies by simultaneous application of two nuclear resonance spectroscopic methods at low temperatures: 63,65Cu nuclear magnetic resonance (NMR) and 57Fe Mössbauer Effect. In particular, at approximately 50K temperature we have experimentally observed rapid deviation of CuFeS2 relaxation parameters from what is normally considered as standard behavior typical for the majority of semiconductors. On the basis of the experimental data obtained and their analysis, some aspects of electronic structure and physical properties of CuFeS2 are presented and discussed.[1] C.I. Pearce, R.A.D. Patrick, D.J. Vaughan, C.M.B. Henderson, G. van der Laan, Geochim. Cosmochim.Acta 70 (2006) 4635. [2] L. V. Kradinova, A. M. Polubotko, V. V. Popov, V. D. Prochukhan, Yu. V. Rud’, V. E. Skoriukin, Semicond.Sci.Technol. 8, 1616 (1993). [3] K. Sato, Y. Harada, M. Taguchi, S. Shin, A. Fujimori, Characterization of Fe 3d states in CuFeS2 by resonant X-ray emission spectroscopy, Phys. Status Solidi A 206, No. 5, 1096–1100 (2009). [4] J.C. Woolley, A.-M. Lamarche, G. Lamarche, M. Quintero, I.P. Swainson, T.M. Holden, Low temperature magnetic behaviour of CuFeS2 from neutron diffraction data, Journal of Magnetism and Magnetic Materials L62 (1996) 347-354 [5] H. N. Ok, K. S. Back, E. J. Choi, Mossbauer study of antiferromagnetic CuFeS1-xSex, Phys.Rev.B, vol.50(14), 10327-10330, 1994. [6] V.M. Bouznik, Nuclear resonance in ionic crystals, Nauka, Novosibirsk, 1981

NQR/NMR and Mössbauer spectroscopy of sulfides: Potential and versatility

Nuclear quadrupole resonance (NQR), nuclear magnetic resonance (NMR) and nuclear gamma-resonance (NGR or Mössbauer Effect) methods are generally described as highly sensitive tools in studies of local electronic structure and symmetry in solid-state materials. This is due to high informativity in electronic structure investigations, high resolution in phase-structural diagnostics (down to nano-scale), possibility to study polycrystalline and complex compounds, and to the non-destructive character of these methods. As applied to Earth sciences, both NQR/NMR and Mössbauer spectroscopy methods contribute to mineralogical material science and mineral physics. Another important aspect is the fact that these methods, as demonstrated recently, belong to unique techniques suitable for on-line bulk mineralogical analysis. This includes remotely operated sensors used with conveyor systems in mining/materials handling and similar applications where real-time data collection/processing provides significant commercial benefits. These developments open new pathways for NQR/NMR and Mössbauer spectroscopy applications. Notably, NQR/NMR and Mössbauer effects are observed primarily on different nuclei-probes but provide similar information about the local properties of materials (hyperfine fields, electric field gradients and relaxation effects). This makes NQR/NMR and Mössbauer methods mutually complementary despite their significant technical differences. This paper includes examples of recent applications of NQR, NMR and Mössbauer spectroscopic tools to studies of copper-, antimony- and iron-containing sulfides, demonstrating how these methods can contribute to an improved understanding of geochemical problems. © 2013 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart