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Structure of FeNCN illustrated in a P6 3 /mmc unit cell (left) and FeO in R % 3 (right). The octahedral coordination of the iron is depicted for each Wyckoff position.
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Three-dimensional non-oxidic extended frameworks offer the possibility to design novel materials with unique properties, which can be different from their oxide analogues. Here, we present first experimental results concerning unusual magnetic properties of FeNCN, investigated using Mossbauer spectroscopy and magnetometry between 5 and 380 K. This...
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... obtained parameters at selected temperatures are given in Table 3. In order to improve the stability of the model, the spectra were first fitted with the relative area of the two components as free parameters, and subsequently, we introduced a Debye model 20 for the variation of the relative Lamb-Mössbauer factor. Thus, the relative area in the fit is proportional to the relative amount of the component times the Lamb-Mössbauer factor. Later, the calculated values were used as fixed parameters. The relative areas obtained in the first step and the Debye fit of the second step are depicted in The non-relaxing component in the measured spectra, compo- nent I, was only adjustable with a model that takes into account a non-zero angle y between the axis of the largest principal compo- nent of the electric field gradient and the hyperfine field for all spectra below 350 K. The angle was estimated to be about 901 at room temperature. Considering the three-fold rotation symmetry along the c axis ( Fig. 1), it follows that the principal component V zz of the diagonalised electric field gradient tensor must be along c and the asymmetry parameter must be Z = |V yy À V xx |/V zz = 0. Fig. 2 Mö ssbauer spectra of FeNCN at selected temperatures and the extracted parameters from all measurements. The non-relaxing component, attributed to stoichiometric FeNCN, is depicted in blue for the magnetically ordered phase and in red for the paramagnetic phase. The relaxing compo- nent is depicted in green and the sum of all components in light purple. The relaxation frequency, n, and the angle, y, between the hyperfine field and the c axis are plotted only for components with non-vanishing contribution. Accordingly, the hyperfine field must be in the ab plane at this temperature. The angle y decreases with decreasing temperature to y = 601 at 10 K. This angle corresponds to the angle between the Fe-N bond and the c axis. Close to the magnetic transition, i.e., above 320 K, the parameter y needed to be fixed to 901 in order to obtain a reliable adjustment. At room temperature, an isomer shift, d = 1.04 mm s À1 , characteristic of high-spin Fe 2+ is obtained for component I. This isomer shift is thus quite similar to wüstite with d E 0.95- 1.02 mm s À1 , 21 although the local environment is modified from an oxygen to nitrogen coordination but with similar symmetry. The measured isomer shift is given by the sum of the genuine isomer shift and a relativistic correction, called second- order Doppler shift. The temperature behaviour of the isomer shift was fitted within the Debye model. 20 A Mössbauer temperature for the second-order Doppler shift 20 of 451(30) K was obtained. The observed hyperfine magnetic field exhibits a remarkable behaviour, it increases below the Néel temperature, reaches a maximum at E300 K and then starts to decrease. Furthermore, the maximum at 5 T is also quite small for usual solids. We attribute component I to the stoichiometric FeNCN material. Note that component I shows a slightly broadened linewidth of E0.35 mm s À1 at all temperatures, a broadening that could indicate small deviations in the local environment of the iron ...
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... the contributions B D produced from the dipolar inter- action, B L produced from the electronic orbital momentum and B S related to the Fermi contact term. The first two terms are usually small in iron compounds 31 and thus we first focus on the Fermi contact term, which describes the interaction of s-electrons with the nucleus. Because the s-electrons are paired, their contribution is due to their polarization by d-electrons and is quite large. 32 Consequently, possible effects of d-electron configuration need to be considered as they may change the contribution of the Fermi contact term. One possibility is that the octahedral environment of the iron ion in combination with the high-spin state produces a -potentially dynamic -Jahn-Teller effect. We thus have to determine the electronic ground state of the d-shell. The Fe 2+ ion in the trigonally distorted octahedral environment formed by the NCN 2À groups, as depicted in Fig. 1, has been employed as input for the Effective Hamiltonian Crystal Field (EHCF) method. 33,34 This calculation reveals the ground state of the Fe 2+ ion to be high-spin, in agreement with previous calcula- tions 11 and the observed isomer shift. The octahedral environ- ment leads to the 5 T 2g ground state. The trigonal distortion of the octahedral field, induced by the NCN units, further splits this state to the 5 A 1 state and the spatially degenerate 5 E states. Our calculation by the EHCF method shows that the true ground state is precisely the spatially non-degenerate 5 A 1 state, in agreement with the negative sign of the quadrupole inter- action as also outlined in ref. 31. In the case of a 5 E ground state, the quadrupole interaction would be positive. The 5 E state is estimated to be 320 K above the ground state. Although this calculation is close to the border of its precision, it may indicate a possible thermal population of the 5 E states. This thermal population is directly seen in the temperature depen- dence of the quadrupole interaction. An estimation of the temperature-dependent quadrupole interaction according to the Ingalls model, 35 with or without lattice contribution, leads to a splitting between the 5 A 1 and 5 E states ranging between 500 and 900 K. Due to the 5 A 1 ground state and the absence of any step-like change 36 in isomer shift or quadrupole splitting a (dynamic) Jahn-Teller effect can be ruled ...
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... usage of NCN 2À as a connecting bridge has a long history, beginning with the fertilizer CaNCN. 3 Investigations of other carbodiimide compounds of alkaline, alkaline-earth metals and other elements followed in the last decades. 3 The investigation of magnetic interactions mediated by such inorganic ligands was initiated more recently. First results were achieved in the field of metal organic frameworks with polymeric metal cyanide compounds, whereby it was found that short bridges (as azido-, cyano-or oxo-bridges) are necessary in order to obtain a strong magnetic coupling between the metal ions. 4,5 Furthermore, magnetic coupling was observed in dicyanamide and tricyanomethanide compounds. 4 In the last decade, different transition metal monoxide analogues bearing the NCN 2À bridges were prepared as extended non-oxidic frameworks and charac- terized structurally and magnetically. 3,6,7 In 2008, the synthesis of FeNCN was reported by Liu et al. with first structural and magnetometric investigations. 7,8 FeNCN crystallizes in the P6 3 /mmc (194) space group at room temperature, with completely linear NCN 2À bridges. 8 The structure can be seen as alternating Fe 2+ and NCN 2À planes (Fig. 1). The local environment of each iron comprises six nitrogens, coordi- nating the iron cation in a slightly distorted octahedron with site symmetry % 3m. On the other hand, the carbodiimide is found in a trigonal iron prism with a structural motif that resembles the NiAs type. The corresponding Fe-Fe and Fe-N bond lengths are given in Table 1. The first susceptibility measurements revealed a Néel temperature of 345 K. 7 The exchange constants obtained by a Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany. E-mail: r.hermann@fz-juelich. de density functional calculations (DFT) indicate a weak ferro- magnetic coupling of the spins within the iron plane and a leading antiferromagnetic coupling between adjacent planes. 9 Nonethe- less, DFT is notoriously unreliable to find the real ground state, also for FeNCN, 10 and DFT exchange parameters have no clear meaning. Many-particle methods are a better choice. 11 For comparison, the analogous iron monoxide has essentially a defect NaCl structure at room temperature, which distorts rhombohedrally along the [111] direction below the Néel temperature, T N = 198 K. 14 The crystal structure at 12 K is R% 3 (148). 12 The magnetic order is ferromagnetic in the (111) planes but antiferromagnetic with respect to neighbouring planes, with moments pointing in the [111] direction. 14 Stoichiometric FeO is not stable under ambient conditions and thus always cation deficient. Just as for FeNCN, one can more or less artificially represent FeO as a layered structure in the [111] direction ( Fig. 1) but containing four different iron sites, with site symmetry % 3,% 3,% 1 and % 1, respectively. The local environment of the iron ion is a distorted octahedral coordination by oxygen atoms in each case. The inter-atomic distances for this material are also given in Table 1. In summary, iron monoxide and iron carbodiimide exhibit a similar local iron environment with a mean nearest neighbour distance of about 2.2 Å in an octahedral coordination by oxygen or nitrogen, respectively. Furthermore, both compounds exhibit a similar antiferromagnetic coupling, although the iron- iron distances between adjacent layers are quite different. It is also remarkable that the Néel temperature of the FeNCN is larger than for FeO. This increase in transition temperature sets the iron carbodiimide apart from the manganese, cobalt and nickel carbo- diimide, which exhibit a lower transition temperature as compared to the corresponding oxides (see Table 2). Furthermore, the Néel temperature is in the order of the d-shell filling for the oxides but not for the carbodiimides, whose order is broken by FeNCN only. Consequently, stronger exchange interactions might take place in FeNCN or the non-stoichiometry in the metastable FeO causes non-uniformity of the magnetic interaction and leads to the lower transition temperature. However, the iron carbodiimide is thus a particularly attractive target for magnetic investigations using Mössbauer spectroscopy and ...
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... usage of NCN 2À as a connecting bridge has a long history, beginning with the fertilizer CaNCN. 3 Investigations of other carbodiimide compounds of alkaline, alkaline-earth metals and other elements followed in the last decades. 3 The investigation of magnetic interactions mediated by such inorganic ligands was initiated more recently. First results were achieved in the field of metal organic frameworks with polymeric metal cyanide compounds, whereby it was found that short bridges (as azido-, cyano-or oxo-bridges) are necessary in order to obtain a strong magnetic coupling between the metal ions. 4,5 Furthermore, magnetic coupling was observed in dicyanamide and tricyanomethanide compounds. 4 In the last decade, different transition metal monoxide analogues bearing the NCN 2À bridges were prepared as extended non-oxidic frameworks and charac- terized structurally and magnetically. 3,6,7 In 2008, the synthesis of FeNCN was reported by Liu et al. with first structural and magnetometric investigations. 7,8 FeNCN crystallizes in the P6 3 /mmc (194) space group at room temperature, with completely linear NCN 2À bridges. 8 The structure can be seen as alternating Fe 2+ and NCN 2À planes (Fig. 1). The local environment of each iron comprises six nitrogens, coordi- nating the iron cation in a slightly distorted octahedron with site symmetry % 3m. On the other hand, the carbodiimide is found in a trigonal iron prism with a structural motif that resembles the NiAs type. The corresponding Fe-Fe and Fe-N bond lengths are given in Table 1. The first susceptibility measurements revealed a Néel temperature of 345 K. 7 The exchange constants obtained by a Jülich Centre for Neutron Science JCNS and Peter Grünberg Institute PGI, JARA-FIT, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany. E-mail: r.hermann@fz-juelich. de density functional calculations (DFT) indicate a weak ferro- magnetic coupling of the spins within the iron plane and a leading antiferromagnetic coupling between adjacent planes. 9 Nonethe- less, DFT is notoriously unreliable to find the real ground state, also for FeNCN, 10 and DFT exchange parameters have no clear meaning. Many-particle methods are a better choice. 11 For comparison, the analogous iron monoxide has essentially a defect NaCl structure at room temperature, which distorts rhombohedrally along the [111] direction below the Néel temperature, T N = 198 K. 14 The crystal structure at 12 K is R% 3 (148). 12 The magnetic order is ferromagnetic in the (111) planes but antiferromagnetic with respect to neighbouring planes, with moments pointing in the [111] direction. 14 Stoichiometric FeO is not stable under ambient conditions and thus always cation deficient. Just as for FeNCN, one can more or less artificially represent FeO as a layered structure in the [111] direction ( Fig. 1) but containing four different iron sites, with site symmetry % 3,% 3,% 1 and % 1, respectively. The local environment of the iron ion is a distorted octahedral coordination by oxygen atoms in each case. The inter-atomic distances for this material are also given in Table 1. In summary, iron monoxide and iron carbodiimide exhibit a similar local iron environment with a mean nearest neighbour distance of about 2.2 Å in an octahedral coordination by oxygen or nitrogen, respectively. Furthermore, both compounds exhibit a similar antiferromagnetic coupling, although the iron- iron distances between adjacent layers are quite different. It is also remarkable that the Néel temperature of the FeNCN is larger than for FeO. This increase in transition temperature sets the iron carbodiimide apart from the manganese, cobalt and nickel carbo- diimide, which exhibit a lower transition temperature as compared to the corresponding oxides (see Table 2). Furthermore, the Néel temperature is in the order of the d-shell filling for the oxides but not for the carbodiimides, whose order is broken by FeNCN only. Consequently, stronger exchange interactions might take place in FeNCN or the non-stoichiometry in the metastable FeO causes non-uniformity of the magnetic interaction and leads to the lower transition temperature. However, the iron carbodiimide is thus a particularly attractive target for magnetic investigations using Mössbauer spectroscopy and ...
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Citations
... Since NPD data suggest no departure from average cubic site symmetry for Fe, this large quadrupole suggests either substantial local distortions or, more likely, a large valence contribution to the quadrupole splitting. A similar observation was reported for FeNCN (65), where carbodiimide acts as a rigid linear oxygen analog. Future work is needed to assess whether iron carries an orbital magnetic moment in this FeO-HEO. ...
High-entropy oxides (HEOs) have aroused growing interest due to fundamental questions relating to their structure formation, phase stability, and the interplay between configurational disorder and physical and chemical properties. Introducing Fe(II) and Mn(II) into a rocksalt HEO is considered challenging, as theoretical analysis suggests that they are unstable in this structure under ambient conditions. Here, we develop a bottom-up method for synthesizing Mn- and Fe-containing rocksalt HEO (FeO-HEO). We present a comprehensive investigation of its crystal structure and the random cation-site occupancy. We show the improved structural robustness of this FeO-HEO and verify the viability of an oxygen sublattice as a buffer layer. Compositional analysis reveals the valence and spin state of the iron species. We further report the antiferromagnetic order of this FeO-HEO below the transition temperature ~218 K and predict the conditions of phase stability of Mn- and Fe-containing HEOs. Our results provide fresh insights into the design and property tailoring of emerging classes of HEOs.
... Fig. 1a is the schematic illustrating the crystal structure of FeNCN, which has an orthorhombic symmetry structure and belongs to the space group of P63/mmc [28]. Fe 2+ are coordinated by six N ions to form octahedrons (FeN 6 ), carbon atoms are connected to N atoms between FeN 6 layers and the formed NCN 2− anions (the pseudo-sulfide anions) are alternately arranged along the trigonal axis [29]. The FeNCN was synthesized by calcination method under argon gas using the ferric ammonium oxalate and urea as precursors [30]. ...
Exploring highly reactive anode materials is crucial for further development of potassium ion batteries (PIBs). Conversion-type materials have the merit of high energy density as anode for PIBs, while suffering from inferior stability and poor rate capability. Herein, we propose to utilize iron carbodiimide (FeNCN) as the anode for PIBs to achieve stable and high-rate potassium storage performance for the first time. The smaller electronegativity and strong covalent bonding structure of FeNCN facilitate improving the charge transfer kinetics of battery systems. Consequently, the FeNCN anode deliver a high reversible capacity (515 mAh g⁻¹ at 50 mA g⁻¹) and remarkable long-life span over 350 cycles with capacity retention of 90% (133 days, current density 100 mA g⁻¹). Moreover, the mechanism for potassium ion storage of FeNCN was revealed by in-situ XRD, ex-situ XPS, and FT-IR. The feasibility of FeNCN as an anode for PIBs paves the way for transition metal (Cr, Mn, Fe, and Co) carbodiimides to be investigated as potential energy storage materials.
... Especially, the effect is expected in the presence of a significant orbital field contribution usually observed as an anisotropy of the electronic g-factor 45,60 . A high electronegativity of Ir favors high covalency of Ir-O bonds, reducing the Fermi contact field and increasing the orbital field contribution to the hyperfine field [61][62][63] . A strong anisotropy in the electronic g-factors in Sr 2 IrO 4 observed by ESR in ref. 64 supports this hypothesis. ...
The high brilliance of modern synchrotron radiation sources facilitates experiments with high-energy x-rays across a range of disciplines, including the study of the electronic and magnetic correlations using elastic and inelastic scattering techniques. Here we report on Nuclear Resonance Scattering at the 73 keV nuclear level in 193Ir. The transitions between the hyperfine split levels show an untypically high E2/M1 multi-polarity mixing ratio combined with an increased sensitivity to certain changes in the hyperfine field direction compared to non-mixing transitions. The method opens a new way for probing local magnetic and electronic properties of correlated materials containing iridium and provides novel insights into anisotropic magnetism in iridates. In particular, unexpected out-of-plane components of magnetic hyperfine fields and non-zero electric field gradients in Sr2IrO4 have been detected and attributed to the strong spin-orbit interaction in this iridate. Due to the high, 62% natural abundance of the 193Ir isotope, no isotopic enrichment of the samples is required, qualifying the method for a broad range of applications.
... Especially, the ef- fect is expected in the presence of significant orbital field contribution and interaction with the lattice as reported in Ref. [55]. An enhanced electronegativity of Ir also favors high covalency of Ir-O bonds, reducing the Fermi contact field and increasing the orbital field contribution to the hyperfine field [56][57][58]. In accordance with this statement, a strong anisotropy in electronic g-factors in Sr 2 IrO 4 was observed by ESR in Ref. [59]. ...
The high brilliance of the modern synchrotron radiation sources facilitates experiments with high energy x-rays. In this Letter we report on Nuclear Resonance Scattering at the 73 keV nuclear level in 193Ir. The transitions between the hyperfine split levels show an exceptionally large E2/M1 multi-polarity mixing ratio combined with an increased sensitivity to certain changes in the hyperfine field direction compared to non-mixing transitions. The method opens a new way for probing local magnetic and electronic properties of correlated materials containing iridium and provides novel insights into their anisotropic magnetism. In particular, unexpected out-of-plane components of magnetic hyperfine fields and non-zero electric field gradients in Sr2IrO4 have been detected and attributed to the presence of strong spin-orbit interaction. Due to the high, 62% natural abundance of the 193Ir isotope, no isotopic enrichment of the samples is required, qualifying the method for a broad range of applications.
... Measuring the temperature dependence of the quadrupole splitting can reveal the level splitting of the ground state in iridates [54]. The theoretical model for the treatment of temperature dependence of quadrupole splitting exists [168], widely used for studies of crystal fields in 57 Fe compounds (3d electron systems) [54,190] and can be applied to iridates. ...
This thesis shows the first synchrotron-based Mössbauer spectroscopy studies on iridium containing compounds and first vibrational spectroscopy on Sb containing compounds carried out at the P01 beamline of PETRA III. In this context, two types of x-ray monochromators have been developed: a monochromator for 73 keV photons with medium energy resolution, and a high-resolution backscattering monochromator based on a sapphire crystal. The monochromator for 73 keV x-rays is the key instrument for hyperfine spectroscopy on Iridium compounds, while the sapphire backscattering monochromator is purposed to vibrational spectroscopy on any Mössbauer resonances with the transition energies in the 20-50 keV range. Additionally, the signal detection for nuclear resonance scattering experiments at the beamline was significantly improved during this work, inspired by the high energies and low lifetimes of the employed resonances.
The first synchrotron-based hyperfine spectroscopy on Iridium-containing compounds was demonstrated by NRS on 73 keV resonance in $^{193}$Ir. The results can be interpreted by dynamical theory of nuclear resonance scattering. In this work, special emphasis is set onto the electronic and magnetic properties of Ir nuclei in IrO$_2$ and in Ruddlesden-Popper (RP) phases of strontium iridates Sr$_{n+1}$Ir$_n$O$_{3n+1}$ (n = 0; 1). These systems are well-suited for studies with x-ray scattering techniques since the scattered signal contains vast information about the widely tunable crystallographic and electronic structure of these systems; furthermore, studies with x-rays are less limited by absorption from iridium as it is the case for neutron scattering experiments. The hyperfine parameters in IrO$_2$, SrIrO$_3$ and Sr$_2$IrO$_4$ have been measured via Nuclear Forward Scattering for the first time. Using the dynamical theory of NRS, the temperature and magnetic field dependence of the electric field gradient and magnetic hyperfine field on Ir nucleus have been determined for these compounds. In order to broaden the perspectives of NRS with the 73 keV resonance the first room temperature NRS on iridium metal is carried out. The results demonstrate NRS as a powerful research tool for the studies of iridium physics due to the high energy of the resonant photons and the high, 63% natural abundance of the $^{193}$Ir isotope under study, paving the way for studies of magnetism and electronic properties under extreme conditions.
The second part of this work is dedicated to vibrational spectroscopy with Nuclear Inelastic Scattering (NIS). A sapphire backscattering monochromator was designed, installed and tested at the beamline. It provides high energy resolution due to the sub-mK temperature control, though the resolution is limited from theoretically proposed sub-meV to meV by the quality of currently available sapphire crystals. With this device the energy resolution of 1.3(1) meV at 23.88 keV and of 3.2(4) meV at 37.13 keV was achieved. Following this development, the vibrational spectra of antimony in defect pyrochlore Ag-Sb-O compounds have been measured by means of NIS at 37.13 keV. Density of phonon states for the Sb(III) and for the Sb(V) site has been revealed. The difference in site-specific antimony modes illustrates the importance of lattice dynamics for the engineering of these compounds.
University of Hamburg, 2017. Thesis is published at http://ediss.sub.uni-hamburg.de/volltexte/2017/8468/
... [25] Moreover, plenty of interesting physico-chemical properties are revealed by comparing metal oxides with the respective carbodiimides (such as those shown in refs. [26][27][28][29]) and recently, copper and cobalt carbodiimides were applied as non-oxidic wateroxidation heterogeneous catalysts, with a dual photochemical and electrocatalytic activity in neutral and basic media. [30,31] A recent report on the use of carbodiimides in Li-ion batteries claims that MnNCN is not electrochemically active. ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
(EN)The invention relates to the use of a metal carbodiimide or a metal cyanamide as a new active material for a negative electrode, a negative electrode comprising said metal carbodiimide or metal cyanamide, its preparation method, a battery comprising said negative electrode, and a method for the preparation of a composite material.(FR)L'invention concerne l'utilisation d'un carbodiimide métallique ou d'un cyanamide métallique en tant que nouveau matériau actif pour une électrode négative, une électrode négative comprenant ce carbodiimide métallique ou ce cyanamide métallique, son procédé de préparation, une batterie comprenant l'électrode négative, et un procédé pour la préparation d'un matériau composite.
... [25] Moreover,p lenty of interesting physico-chemical properties are revealed by comparing metal oxides with the respective carbodiimides (such as those shown in refs. [26][27][28][29]) and recently,copper and cobalt carbodiimides were applied as non-oxidic wateroxidation heterogeneous catalysts,with adual photochemical and electrocatalytic activity in neutral and basic media. [30,31] A recent report on the use of carbodiimides in Li-ion batteries claims that MnNCN is not electrochemically active. ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages.S pectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components:t he main component is am agnetic octet with five resolved lines typical for divalent iron with ac ombined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve);the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity,s uch as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages.S pectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components:t he main component is am agnetic octet with five resolved lines typical for divalent iron with ac ombined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve);the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity,s uch as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
FeNCN can be efficiently used as negative electrode material for alkali metal ion batteries.
... [25] Moreover, plenty of interesting physico-chemical properties are revealed by comparing metal oxides with the respective carbodiimides (such as those shown in refs. [26][27][28][29]) and recently, copper and cobalt carbodiimides were applied as non-oxidic wateroxidation heterogeneous catalysts, with a dual photochemical and electrocatalytic activity in neutral and basic media. [30,31] A recent report on the use of carbodiimides in Li-ion batteries claims that MnNCN is not electrochemically active. ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
Wir weisen die elektrochemische Aktivität von Übergangsmetallcarbodiimiden gegenüber Lithium und Natrium nach. Insbesondere das Eisencarbodiimid FeNCN läßt sich effektiv als negatives Elektrodenmaterial für Alkalimetallionenbatterien verwenden, ähnlich dem Oxidanalogon FeO. Auf der Basis von 57Fe-Mößbauer- und infrarotspektroskopischen (IR) Daten kann der elektrochemische Reaktionsmechanismus bei Entladung und Beladung durch die reversible Umwandlung von Fe-NCN- in Li/Na-NCN-Bindungen erklärt werden. Diese neuen Elektrodenmaterialien weisen höhere Kapazitäten als die etablierten negativen Referenzelektroden wie Graphit oder Hartkohlenstoff auf. Im Gegensatz zu seinem Oxidanalogon benötigt Eisencarbodiimid keine aufwendige Vorbehandlung (Nanopräparation, spezielle Texturen, Beschichtung usw.), um eine lange Lebensdauer bei Stromdichten bis zu 9 A g−1 für hunderte von Lade-/Entladezyklen zu erreichen. Ähnlich zur Eisenverbindung können einige andere Übergangsmetallcarbodiimide Mx(NCN)y mit M=Mn, Cr, Zn ebenso erfolgreich gegen Lithium und Natrium zyklisieren. Ihre elektrochemische Aktivität und Leistung öffnet den Weg zum Design einer neuartigen Klasse von Anodenmaterialien.
... [25] Moreover, plenty of interesting physico-chemical properties are revealed by comparing metal oxides with the respective carbodiimides (such as those shown in refs. [26][27][28][29]) and recently, copper and cobalt carbodiimides were applied as non-oxidic wateroxidation heterogeneous catalysts, with a dual photochemical and electrocatalytic activity in neutral and basic media. [30,31] A recent report on the use of carbodiimides in Li-ion batteries claims that MnNCN is not electrochemically active. ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
... In situ Mçssbauer spectra ( Figure 4) were acquired at different cycling stages. Spectrum (a) of the initial powder is similar to that previously reported [29] and can be fitted by two components: the main component is a magnetic octet with five resolved lines typical for divalent iron with a combined quadrupolar and magnetic interaction and corresponds to antiferromagnetically ordered high-spin Fe 2+ (red curve); the weak doublet centered at 0.4 mm s À1 is attributed to slowly relaxing Fe 3+ (gray line), as discussed by Herlitschke et al., [29] which is most probably due to an impurity, such as an amorphous oxidized Fe(NCNH) 2 precursor. Spectrum (b) collected at the end of the discharge consists of two doublets with similar isomer shifts (about 0.05 mm s À1 ) and appreciably different quadrupole splittings (0.37 and 0.87 mm s À1 ). ...
We report evidence for the electrochemical activity of transition-metal carbodiimides versus lithium and sodium. In particular, iron carbodiimide, FeNCN, can be efficiently used as negative electrode material for alkali-metal-ion batteries, similar to its oxide analogue FeO. Based on 57Fe Mössbauer and infrared spectroscopy (IR) data, the electrochemical reaction mechanism can be explained by the reversible transformation of the Fe−NCN into Li/Na−NCN bonds during discharge and charge. These new electrode materials exhibit higher capacity compared to well-established negative electrode references such as graphite or hard carbon. Contrary to its oxide analogue, iron carbodiimide does not require heavy treatments (such as nanoscale tailoring, sophisticated textures, or coating) to obtain long cycle life with current density as high as 9 A g−1 for hundreds of charge–discharge cycles. Similar to the iron compound, several other transition-metal carbodiimides Mx(NCN)y with M=Mn, Cr, Zn can cycle successfully versus lithium and sodium. Their electrochemical activity and performance open the way to the design of a novel family of anode materials.
... In the cluster calculation, the 3d-electrons were explicitly included only for the central Fe(II) ion, the remaining Fe(II) ions were modeled by Be atoms (no d-electrons) with semiempirical parameters for valence s-and p-orbitals corresponding to 4s-and 4p-atomic orbitals of Fe(II) and predicted the ground state to be highspin 5 A 1 state in agreement with the observed magnetic moment. More detailed consideration [55] confirms this finding which is agreement with the negative sign of the QS in the observed M€ oßbauer spectrum. [55] In the surrounding of nitrogen donor atoms the Fe 21 ion at the experimental geometry of FeNCN is in the high-spin state. ...
... pirical parameters for valence s-and p-orbitals corresponding to 4s-and 4p-atomic orbitals of Fe(II) and predicted the ground state to be highspin 5 A 1 state in agreement with the observed magnetic moment. More detailed consideration [55] confirms this finding which is agreement with the negative sign of the QS in the observed M€ oßbauer spectrum. [55] In the surrounding of nitrogen donor atoms the Fe 21 ion at the experimental geometry of FeNCN is in the high-spin state. The 5 A 1 state originates from the 5 T 2g term in octahedral symmetry which splits into 5 A 1 and 5 E terms as a result of a trigonal distortion (Fig. 6). That latter derives from the spherically symmetric S5 5=2 de ...
... Dr. M. Herlitschke is acknowledged for kindly providing the results of M€ oßbauer measurements [55] in a numeric form. The authors are thankful to the Referee for the valuable comments which for sure helped to improve the manuscript. ...
We review the basics of the Effective Hamiltonian Crystal Field (EHCF) method originally targeted for calculations of the intra-shell excitations in the d-shells of coordination compounds of the first row transition metal. The formalism employs in the concerted way the McWeeny's group-function approximation and the Lowdin partition technique. It is needed for description of the transition metal complexes with partially filled d-shells where the (static) electronic correlations are manifested. These features are particularly important for electron fillings close to " half shell " ones occurring, for example, in the Fe 21 and Fe 31 ions. Recently we extended this methodology to polynuclear coordination compounds to describe magnetic interactions of the effective spins residing in several open d-shells. This improves the accuracy from about 1000 cm 21 to that of about 100 cm 21 , that is, eventually by an order of magnitude. This approach implemented in the MagAixTic package is applied here to a series of binuclear Fe(III) complexes featuring l-oxygen super-exchange pathways. The results of calculations are in a reasonable agreement with available experimental data and other theoretical studies of protonated bridges. Further we discuss the application of the EHCF to analysis of Mosbauer experiments performed on two organometallic solids: FeNCN and Fe(HNCN) 2 and conjecture a new thermal effect in the latter material. V
