СЛОВО ПРО ПРОФЕСОРА В. В. КРУТІКОВА

The electronic structures of “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), in connection to the recently synthesized Ti9-nFe2+nRu18B8 (n = 1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Through a combination of calculations on specific models and using the rigid band approximation, which is validated by the DOS curves for “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), mixing of Fe and Ti is anticipated at both the 2b- and 4h-chain sites. The model “Ti8.5Fe2.5Ru18B8” (n = 0.5) revealed that both Brewer-type Ti−Ru interactions as well as ligand field splitting of the Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using “Ti6Fe5Ru18B8” (n = 3). A rigid band analysis of the LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ≤ 0.75) and ferrimagnetic ordering at higher Fe content (n \u3e 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fe1-ladder and 4h-chain sites

Torsional selection rules, Raman tensors, and cross sections for degenerate modes of C2H6

16 pages, 12 figures.-- PACS nrs.: 33.20.Tp, 33.15.Mt, 33.70.Fd.We analyze the peculiarities induced by the torsional motion on the Raman spectra of the degenerate vibrational bands of ethane. Selection rules for the Raman transitions between the torsionally split energy levels are derived first in terms of symmetry arguments. Then, their associated intensities are calculated with a model for the torsional dependence of the molecular polarizability. New experimental spectra of the Raman degenerate bands of C2H6, some recorded in jet expansions, are also included and analyzed to show the current state of the problem.This work was supported by the Spanish DGICYT and DGES, research projects PB94-1526 and PB97-1203.Peer reviewe

Шляхи підвищення ефективності використання виробничих ресурсів сільськогосподарських підприємств

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn11Rh18B8 structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain–ladder–chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti8Fe3Ru18B8 is unexpectedly smaller than the recently reported Ti9Fe2Ru18B8 ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest Hc value (28.6 kA/m), measured for Ti7Fe4Ru18B8, lies just at the border of those of hard magnetic materials

Synthese und Charakterisierung von komplexen Iridium-Boriden mit B 4-Einheiten

This work reports about the synthesis and characterization of new intermetallic borides with B4 units. The compounds which have a metallic luster were prepared via a solid state route in an arc welder starting from the elements. The structural characterization was done through X-Ray analysis on single crystals and powder samples. The chemical composition was checked with EDX measurements. In representative cases, quantum chemical calculations accompanied with bonding analysis and a study of the magnetic properties were done. The first part of the present work describes a newly discovered structure, namely the Ti1+xRh2-x+yIr3-yB3-type. The synthesis was optimized followed by a detailed description of the complex crystal structure. These transition metal borides with a metal to boron ratio of 2:1 contain isolated as well as bonded boron atoms in the shape of B4 zigzag units. The very close structural relationship to the Ti1+xOs2-xRuB2-type has been demonstrated in this work. With a suitable theoretical model, the electronic structure was calculated and a detailed bonding analysis has been performed. This analysis revealed that the boron-boron contacts and the boron-metal contacts are responsible for the stability of the structure under investigation. Further experiments were then based on the 3(Ti|M):3Ir:3B-system. With the elements M = Mn-Ni and a Ti:M-ratio of 2:1, another four compounds adopting the newly discovered Ti1+xRh2-x+yIr3-yB3-type have been successfully synthesized. These compounds are best described as solid solutions with the general formula Ti2M1-xIr3+xB3. Due to the substructure of the magnetically active elements, these compounds are interesting concerning their magnetic properties. Because it was until now not possible to synthesize the later as phase pure samples, the magnetic properties were studied by using quantum chemical methods. The results of the calculations predict that the compound with M = Mn is ferromagnetic and that the compounds with M = Fe, Co and Ni are paramagnetic. With the elements M = Mo, Ru, W and Re and a Ti:M-ratio of 2:1 the presence of the Ti1+xRh2-x+yIr3-yB3-type could also be shown. The later compounds are best described with the general formula Ti1+xM2-xIr3B3. With a variation of the Ti:M-Ratio to 1:2, it could be shown, that the desired structure is not forming when the elements M = Co and Ni are used. With M = Fe a very similar compound compared to the one with M = Fe and Ti:M = 2:1 was identified. Surprisingly, with M = Mn a compound crystalizing in the Ti1+xOs2-xRuB2-type was identified, thus a change of the crystal structure occurred. With the elements M = V and Cr and the Ti1+xOs2-xRuB2-type could be successfully synthesized with both ratios Ti:M = 1:2 and Ti:M = 2:1. The new compounds adopting the Ti1+xOs2-xRuB2-type are best described with the general formula TiM1-xIr2+xB2. Furthermore a structural comparison of the related Ti1+xOs2-xRuB2-type and the Ti1+xRh2-x+yIr3-yB3-type was performed. Besides the different similarities and differences it was shown, that the Ti1+xRh2-x+yIr3-yB3-type can be generated out of the Ti1+xOs2-xRuB2-type by the use of simple geometric operations. A group subgroup relationship between both types does not exist. Experiments with the aim to substitute titanium in the 3(Ti|M):3Ir:3B-system with other elements, lead to the discovery of a new compound crystallizing in the Mo2IrB2-type. The chemical formula of the new compound is V1.10(1)Nb0.90(1)IrB2, which at the same time is the first quaternary representative of the Mo2IrB2-type. This compound also forms B4 zigzag units as found in the compounds of the Ti1+xRh2-x+yIr3-yB3-type. Alongside the structural characterization of this new compound, the electronic structure was calculated followed by a bonding analysis

Synthese und Charakterisierung von komplexen Iridium-Boriden mit B 4-Einheiten

This work reports about the synthesis and characterization of new intermetallic borides with B4 units. The compounds which have a metallic luster were prepared via a solid state route in an arc welder starting from the elements. The structural characterization was done through X-Ray analysis on single crystals and powder samples. The chemical composition was checked with EDX measurements. In representative cases, quantum chemical calculations accompanied with bonding analysis and a study of the magnetic properties were done. The first part of the present work describes a newly discovered structure, namely the Ti1+xRh2-x+yIr3-yB3-type. The synthesis was optimized followed by a detailed description of the complex crystal structure. These transition metal borides with a metal to boron ratio of 2:1 contain isolated as well as bonded boron atoms in the shape of B4 zigzag units. The very close structural relationship to the Ti1+xOs2-xRuB2-type has been demonstrated in this work. With a suitable theoretical model, the electronic structure was calculated and a detailed bonding analysis has been performed. This analysis revealed that the boron-boron contacts and the boron-metal contacts are responsible for the stability of the structure under investigation. Further experiments were then based on the 3(Ti|M):3Ir:3B-system. With the elements M = Mn-Ni and a Ti:M-ratio of 2:1, another four compounds adopting the newly discovered Ti1+xRh2-x+yIr3-yB3-type have been successfully synthesized. These compounds are best described as solid solutions with the general formula Ti2M1-xIr3+xB3. Due to the substructure of the magnetically active elements, these compounds are interesting concerning their magnetic properties. Because it was until now not possible to synthesize the later as phase pure samples, the magnetic properties were studied by using quantum chemical methods. The results of the calculations predict that the compound with M = Mn is ferromagnetic and that the compounds with M = Fe, Co and Ni are paramagnetic. With the elements M = Mo, Ru, W and Re and a Ti:M-ratio of 2:1 the presence of the Ti1+xRh2-x+yIr3-yB3-type could also be shown. The later compounds are best described with the general formula Ti1+xM2-xIr3B3. With a variation of the Ti:M-Ratio to 1:2, it could be shown, that the desired structure is not forming when the elements M = Co and Ni are used. With M = Fe a very similar compound compared to the one with M = Fe and Ti:M = 2:1 was identified. Surprisingly, with M = Mn a compound crystalizing in the Ti1+xOs2-xRuB2-type was identified, thus a change of the crystal structure occurred. With the elements M = V and Cr and the Ti1+xOs2-xRuB2-type could be successfully synthesized with both ratios Ti:M = 1:2 and Ti:M = 2:1. The new compounds adopting the Ti1+xOs2-xRuB2-type are best described with the general formula TiM1-xIr2+xB2. Furthermore a structural comparison of the related Ti1+xOs2-xRuB2-type and the Ti1+xRh2-x+yIr3-yB3-type was performed. Besides the different similarities and differences it was shown, that the Ti1+xRh2-x+yIr3-yB3-type can be generated out of the Ti1+xOs2-xRuB2-type by the use of simple geometric operations. A group subgroup relationship between both types does not exist. Experiments with the aim to substitute titanium in the 3(Ti|M):3Ir:3B-system with other elements, lead to the discovery of a new compound crystallizing in the Mo2IrB2-type. The chemical formula of the new compound is V1.10(1)Nb0.90(1)IrB2, which at the same time is the first quaternary representative of the Mo2IrB2-type. This compound also forms B4 zigzag units as found in the compounds of the Ti1+xRh2-x+yIr3-yB3-type. Alongside the structural characterization of this new compound, the electronic structure was calculated followed by a bonding analysis

Scaffolding, Ladders, Chains, and Rare Ferrimagnetism in Intermetallic Borides: Synthesis, Crystal Chemistry and Magnetism

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn11Rh18B8 structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain–ladder–chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti8Fe3Ru18B8 is unexpectedly smaller than the recently reported Ti9Fe2Ru18B8 ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest Hc value (28.6 kA/m), measured for Ti7Fe4Ru18B8, lies just at the border of those of hard magnetic materials.Reprinted (adapted) with permission from Inorg. Chem., 2011, 50 (13), pp 6289–6296. Copyright 2011 American Chemical Society.</p