M. Jansen

Max Planck Institute for Chemical Physics of Solids, Dresden, Saxony, Germany

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Publications (498)736.53 Total impact

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    ABSTRACT: Substitution of Bi for Ca in the red-violet pigment Ca10(PO4)6CuyO2H2-y-δ has been studied in order to access possibilities to vary the color of the pigment. Synthesized compounds have been investigated by powder X-ray diffraction, diffuse reflectance (ultraviolet-visible-near infrared range) and Raman spectroscopy. Initial Bi-free samples contain Cu in the hexagonal channels, and a fraction of the Cu atoms constitutes recently discovered chromophore [O–CuIII–O]−-units. Bi3+ occupies Ca2+ position in the hexagonal channel walls and causes the reduction of the chromophore concentration. A small fraction of Cu2+ substitutes Ca2+ and forms a new chromophore characterized by the main absorption band at 400 nm and the resonant Raman band at 593 cm−1. Consequently, Bi-doping suppresses the initial red-violet color of the pigment while a yellow tint emerges. This may open an opportunity to develop new less-toxic yellow pigments.
    Dyes and Pigments 02/2015; 113:96–101. · 3.53 Impact Factor
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    ABSTRACT: We have investigated the structural and magnetic transitions in CsCoO$_2$ using calorimetric measurements, neutron powder diffraction (NPD), density functional theory (DFT) calculations and muon-spin relaxation ($\mu$SR) measurements. CsCoO$_2$ exhibits three-dimensional long-range antiferromagnetic (AFM) order at 424~K, resulting in antiferromagnetic alignment of chains of ferromagnetically ordered Co-Co spin dimers. Although there is no change in magnetic structure around a structural transition at $T^{*}=100$~K, the resulting bifurcation of corner-shared Co--O--Co bond angles causes a weakening of the AFM interaction for one set of bonds along the chains. Consequently, the system undergoes a complex freezing out of relaxation processes on cooling.
    10/2014;
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    ABSTRACT: Using 133Cs nuclear magnetic resonance, we follow the magnetic response of CsO2, coming from the p-orbital S=1/2 spins of magnetic O2- anions, across the structural phase transition occuring at Ts1=61 K on cooling. Above Ts1, where spins form a square magnetic lattice, we extract and model an anomalous temperature dependence of the exchange coupling J(T) originating from thermal librations of O2- dumbbells. Below Ts1, we detect a clear sign of the spin Tomonaga-Luttinger liquid demonstrating the formation of magnetic spin chains as a result of the static tilt of O2- dumbbells and accompanying orbital ordering. The extracted J(T) allows us to conclude that orbital overlaps in the orbitally-ordered state are maximized, thereby providing an important clue about the microscopic origin of orbital ordering.
    09/2014;
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    ABSTRACT: Frustrated magnets can exhibit many novel forms of order when exposed to high magnetic fields, however, much less is known about materials where frustration occurs in the presence of itinerant electrons. Here we report thermodynamic and transport measurements on micron-sized single crystals of the triangular-lattice metallic antiferromagnet 2H-AgNiO2, in magnetic fields of up to 90 T and temperatures down to 0.35 K. We observe a cascade of magnetic phase transitions at 13.5 20, 28 and 39T in fields applied along the easy axis, and we combine magnetic torque, specific heat and transport data to construct the field-temperature phase diagram. The results are discussed in the context of a frustrated easy-axis Heisenberg model for the localized moments where intermediate applied magnetic fields are predicted to stabilize a magnetic supersolid phase. Deviations in the measured phase diagram from this model predictions are attributed to the role played by the itinerant electrons.
    Physical Review B 07/2014; 90:020401(R). · 3.66 Impact Factor
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    ABSTRACT: High-pressure room-temperature angle-dispersive powder X-ray diffraction measurements on Cu 2 S chal-cocite were performed up to 30 GPa using a diamond-anvil cell, He as pressure transmitting medium and synchrotron radiation. Two first-order phase transitions were found at 3.2 and 7.4 GPa. The indexation of the powder diffraction patterns suggests three different monoclinic cells for the low-pressure chalcocite and the two high-pressure phases. Subtle changes in the X-ray diffraction patterns suggest a third pressure-induced transition above 26 GPa. Structural parameters and compressibility are discussed and compared to those reported in a previous study on Cu 2 S nanowires.
    Journal of Alloys and Compounds 05/2014; 610. · 2.73 Impact Factor
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    ABSTRACT: In order to gain new insight in the ZnO system, we performed crystal structure prediction using simulated annealing with an empirical potential and local optimization on ab initio level, both at standard and elevated pressure. We have found the experimentally observed structure types [wurtzite (B4), sphalerite (B3), and rock salt (B1)] in agreement with previous research. In addition, many new interesting modifications were found in different regions of the energy landscape, such as the β-BeO type, the GeP type, the NiAs type, and the so-called "5-5" type modification. At extreme conditions (>150 GPa), we observe a CsCl (B2) type of structure, and as a possible intermediate phase along the NaCl (B1) → CsCl (B2) transition route, we suggest the α-WC (Bh) modification. Furthermore, we have investigated the electronic properties of ZnO structures. Our investigations offer new possibilities of tuning the band gap with pure zinc oxide by employing modifications with different structural arrangements.
    01/2014; 89(7).
  • 11/2013;
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    ABSTRACT: Spin and charge transport: The electronic and structural properties obtained from KC60 (THF)5 ⋅2 THF single crystals are reported. An important finding is the presence of one-dimensional electric conductivity and the observation of counterintuitive anisotropy for electron transport.
    Angewandte Chemie International Edition 10/2013; · 11.34 Impact Factor
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    ABSTRACT: The ideal treatment of patients with perforated diverticulitis is still controversial. Hartmann's procedure has been the treatment of choice for decades, but primary anastomosis with a defunctioning stoma has become an accepted alternative. The aim of this study was to evaluate the stoma reversal rates after these two surgical strategies. A retrospective review of the data from patients with perforated sigmoid diverticulitis between 2002 and 2011 undergoing a Hartmann's procedure (HP) versus a primary anastomosis with a defunctioning stoma (PA) was performed. Additionally, patients were contacted by mail or telephone in March 2012 using a standardized questionnaire. A total of 98 patients were identified: 72 undergoing HP and 26 patients receiving PA. The median follow-up time was 63 months (range 4-118). Whilst 85 % of patients with PA have had their stoma reversed, only 58 % of patients with an HP had a stoma reversal (p = 0.046). The median period until stoma reversal was significantly longer for HP (19 weeks) than for PA (12 weeks; p = 0.03). The 30-day mortality for PA was 12 % as opposed to 25 % for HP (p = 0.167). According to the Clavien-Dindo classification, surgical complications occurred significantly less frequently in patients with PA (p = 0.014). The stoma reversal rates for PA are significantly higher than for HP. Thus, depending on the overall clinical situation, primary resection and anastomosis with a proximal defunctioning stoma might be the optimal procedure for selected patients with perforated diverticular disease.
    International Journal of Colorectal Disease 08/2013; · 2.24 Impact Factor
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    ABSTRACT: We present the results of muon-spin relaxation measurements on the triangular lattice Heisenberg antiferromagnet $\alpha$-KCrO$_{2}$. We observe sharp changes in behaviour at an ordering temperature of $T_{\mathrm{c}}=23$ K, with an additional broad feature in the muon-spin relaxation rate evident at T=13 K, both of which correspond to features in the magnetic contribution to the heat capacity. This behaviour is distinct from both the Li- and Na- containing members of the series. These data may be qualitatively described with the established theoretical predictions for the underlying spin system.
    Physical Review B 07/2013; 88(18). · 3.66 Impact Factor
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    ABSTRACT: Based on ab initio calculations at various pressures meta(stable) modifications of CaN2, LaN2, and TiN2 are predicted.
    ChemInform 06/2013; 44(25).
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    ABSTRACT: The systematic comparison of the atomic structure of solids and clusters has become an important task in crystallography, chemistry, physics and materials science, in particular in the context of structure prediction and structure determination of nanomaterials. In this work, an efficient and robust algorithm for the comparison of cluster structures is presented, which is based on the mapping of the point patterns of the two clusters onto each other. This algorithm has been implemented as the module CCL in the structure visualization and analysis program KPLOT.
    Journal of Applied Crystallography 06/2013; 46(Pt 3):587-593. · 3.34 Impact Factor
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    ABSTRACT: An efficient and robust algorithm for the comparison of clusters is presented. Several illustrative example applications are given, including the screening of sets of clusters generated during global optimizations and Monte Carlo/molecular dymanics simulations, the identification of specific structure fragments inside large clusters, and the study of structure-substructure relations of periodic crystals.
    Journal of Applied Crystallography 04/2013; 46(3). · 3.34 Impact Factor
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    ABSTRACT: An ab initio DFT-based study of the electronic band structure and elastic properties of the new lithium ion conductors Li2B3O4F3 and Li2B6O9F2 has been performed. The hybrid functional B3LYP was employed with the CRYSTAL code, and the local density approximation (LDA) with the VASP code. Starting from the experimentally determined structures, both crystals were computationally optimized. The relaxed structures were found to be very close to the initial, experimental, ones. The band structure shows wide band gaps Eg, near 9–10 eV (B3LYP) or 6–7 eV (LDA), depending on the level of theory applied. The top valence bands of both crystals mainly derive from oxygen and fluorine, and the bottom conduction bands are mainly associated with boron and oxygen. An analysis of the elastic properties of the two compounds has been done, and all coefficients of the elastic stiffness tensor cij and the bulk modulus B are calculated. The interatomic distances, Mulliken charges and overlap populations are discussed from the viewpoint of lithium ion conductivity.
    Journal of Physics and Chemistry of Solids 04/2013; 74(4):624–629. · 1.53 Impact Factor
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    ABSTRACT: We present results of ab initio DFT-based and experimental studies on electrical, piezoelectric and optical properties of the newly synthesized noncentrosymmetric lithium fluorooxoborates, Li2B3O4F3 and Li2B6O9F2. Polar Li2B6O9F2, space group Cc, was found to possess a relatively large spontaneous polarization and some large components of the elasto-electric tensor, compared to non-polar but noncentrosymmetric Li2B3O4F3, space group P212121. Linear and nonlinear optical properties of the crystals are studied theoretically. Second harmonic generation is possible for both crystals, which is demonstrated by calculations of the phase matching conditions and the second order electronic susceptibility. Experimental measurements have confirmed the expected pyroelectric (but not ferroelectric) and piezoelectric properties of Li2B6O9F2. The intensity of second harmonic generation of Li2B6O9F2 has been revealed experimentally to be of the same order of magnitude as that observed in α-SiO2.
    Journal of Physics and Chemistry of Solids 04/2013; 74(4):616–623. · 1.53 Impact Factor
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    ABSTRACT: The magnetic ordering patterns of Rb11Mn8O16 and Cs3Mn2O4 were determined by neutron powder diffraction with and without applied magnetic fields. The crystal structures of these compounds exhibit infinite chains of edge-sharing MnO4 tetrahedra with periodically alternating Mn2+ and Mn3+ valence. Both Rb11Mn8O16 and Cs3Mn2O4 show collinear magnetic order with antiferromagnetic alignment of Mn moments along the chains below the Néel temperatures TN = 38(1) and 13.5(5) K, respectively. In Cs3Mn2O4 the Mn2+ and Mn3+ moments could be separately refined. The full magnetic structure in a zero magnetic field can be viewed as a set of ferrimagnetic chains whose net moments are coupled antiferromagnetically perpendicular to the chain direction. For this compound, we further observe a magnetic field induced transition into a high-field phase with uniformly aligned ferrimagnetic moments.
    Physical review. B, Condensed matter 01/2013; 87(1). · 3.66 Impact Factor
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    ABSTRACT: Metal-pernitride compounds belong to a class of chemical systems in which both the complex ions and the non-bonding electrons may play roles in the formation of their modified crystalline structures. To investigate this issue, the energy landscapes of pernitrides of metals with different maximum valence (M=Ca, Sr, Ba, La, and Ti) were globally explored on the ab initio level at standard and high pressures, thereby yielding possible (meta)stable modifications in these systems together with information on how the landscape changed as function of the valence of the metal cation. For all of the systems in which no compounds had been synthesized so far, we predicted the existence of kinetically stable modifications that should, in principle, be experimentally accessible. In particular, TiN(2) should crystallize in a new structure type, TiN(2) -I.
    Chemistry - An Asian Journal 01/2013; · 4.57 Impact Factor
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    ABSTRACT: The structural behavior of mineral Stromeyerite, AgCuS, has been studied by means of angle-dispersive X-ray diffraction measurements up to 13 GPa and ab initio total-energy calculations. Two high-pressure phase transitions are found at 1.4 and 5.7 GPa, from the initial distorted Ni(2)In-type phase (AuRbS-type, RP, space group Cmc2(1)) through an anti-PbClF-type phase (HP1, space group P4/nmm) to a monoclinic distortion of this latter phase (HP2, space group P2(1)/m). The collapse of the metal-metal interatomic distances at the RP-HP1 transition suggests a stronger metallic behavior of the high-pressure phase. The compressibility of the lattice parameters and the equation of state of the first pressure-induced phase have been experimentally determined. First-principles calculations present an overall agreement with the experimental results in terms of the high-pressure sequence and provide chemical insight into the AgCuS behavior under hydrostatic pressure.
    Inorganic Chemistry 12/2012; · 4.59 Impact Factor
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    ABSTRACT: In this study, the Raman and IR spectra of a large number of isomers of MgF(2) clusters and of possible bulk polymorphs of MgF(2) are calculated and compared with experimental data observed using a low-temperature atom beam deposition. The bulk polymorphs were taken from earlier work, while the cluster modifications for the neutral (MgF(2))(n) (n = 1-10) clusters and charged clusters (up to the trimer anion and cation, (Mg(3)F(7))(-) and (Mg(3)F(5))(+), respectively) are determined in the present work by global energy landscape explorations using simulated annealing. These theoretical calculations are complemented by an experimental study on both the vapor phase and the deposited films of MgF(2), which are generated in a low-temperature atom beam deposition setup for the synthesis of MgF(2) bulk phases. The MgF(2) vapor and film are characterized via Raman spectroscopy of the MgF(2) gas phase species embedded in an Ar-matrix and of the MgF(2)-films deposited onto a cooled substrate, respectively. We find that, in the vapor phase, there are monomers and dimers and charged species to be present in our experimental setup. Furthermore, the results suggest that in the amorphous bulk MgF(2), rutile-like domains are present and MgF(2) clusters similar to those in the matrix. Finally, peaks at about 800 cm(-1), which are in the same range as the A(g) modes of clusters with dangling fluorine atoms connected to three-coordinated Mg atoms, indicate that such dangling bonds are also present in amorphous MgF(2).
    The Journal of Chemical Physics 11/2012; 137(19):194319. · 3.12 Impact Factor

Publication Stats

1k Citations
736.53 Total Impact Points

Institutions

  • 2014
    • Max Planck Institute for Chemical Physics of Solids
      Dresden, Saxony, Germany
  • 1998–2014
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
  • 2011–2013
    • HELIOS Klinikum Emil von Behring
      Berlin Steglitz Zehlendorf, Berlin, Germany
  • 1991–2013
    • University of Bonn
      • • Institute for Inorganic Chemistry
      • • Kekulé Institute of Organic Chemistry and Biochemistry
      Bonn, North Rhine-Westphalia, Germany
  • 2011–2012
    • Complutense University of Madrid
      • Departamento de Química Física I
      Madrid, Madrid, Spain
  • 2008–2011
    • University of Oxford
      • Department of Physics
      Oxford, England, United Kingdom
  • 2010
    • Paul Scherrer Institut
      • Laboratory for Neutron Scattering (LNS)
      Villigen, AG, Switzerland
  • 1997–2008
    • RWTH Aachen University
      • • Klinik für Allgemein-, Viszeral- und Transplantationschirurgie
      • • Neurochirurgische Klinik
      Aachen, North Rhine-Westphalia, Germany
  • 2007
    • Indian Institute of Technology Delhi
      • Department of Chemistry
      New Delhi, NCT, India
  • 1997–2007
    • University Hospital RWTH Aachen
      • Department of Neurology
      Aachen, North Rhine-Westphalia, Germany
  • 2004–2006
    • Universitätsklinikum Jena
      Jena, Thuringia, Germany
    • Russian Academy of Sciences
      • N. N. Semenov Institute of Chemical Physics
      Moskva, Moscow, Russia
  • 2001–2003
    • Moscow State Textile University
      Moskva, Moscow, Russia
  • 2000–2001
    • Max Planck Institute for Intelligent Systems, Stuttgart
      Stuttgart, Baden-Württemberg, Germany