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Holger Kohlmann - One of the best experts on this subject based on the ideXlab platform.
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determination of element deuterium bond lengths in zintl phase Deuterides by 2h nmr
Physical Chemistry Chemical Physics, 2019Co-Authors: Robin Guehne, Henry Auer, Holger Kohlmann, Jurgen Haase, Marko BertmerAbstract:The Zintl phase Deuterides CaSiD4/3, SrSiD5/3, BaSiD2, SrGeD4/3, BaGeD5/3 and BaSnD4/3 were investigated by nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations to reliably determine element–deuterium bond lengths. These compounds show deuterium bound to the polyanion and deuteride ions in tetrahedral cationic voids. With 2H-NMR experiments we characterised the individual signals of the two distinct crystal sites. Quadrupolar coupling constants (CQ) of the anion-binding site were determined as 58 to 78 kHz (Si compounds), 51 to 61 kHz (Ge compounds) and 38 kHz (Sn compound). These values agree well with the quadrupole couplings derived from DFT using optimized structural models. We further calculated the general element–deuterium distance dependency of CQ using DFT methods that allow an accurate determination of bond lengths via the 2H quadrupole interaction. The thus determined bond lengths are evaluated as d(Si–D) = 1.53–1.59 A, d(Ge–D) = 1.61–1.65 A and d(Sn–D) = 1.86 A. Chemical shifts of the anion-binding site range from 0.3 to 1.3 ppm. The isotropic chemical shifts of the tetrahedral sites are 5.1 ppm (CaSiD4/3), 7.0 to 10.0 ppm (Sr compounds) and 10.7 to 11.6 ppm (Ba compounds).
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electron phonon coupling in luminescent europium doped hydride perovskites studied by luminescence spectroscopy inelastic neutron scattering and first principles calculations
Journal of Physical Chemistry C, 2018Co-Authors: Gauthier Lefevre, Holger Kohlmann, Alexander Herfurth, Adlane Sayede, Thomas Wylezich, Sacha Welinski, Pedro Duarte Vaz, Stewart F. Parker, Jean François BlachAbstract:We present a case study on the vibrational coupling of lattice phonons to the electronic 4f7 (8S7/2)–4f65d1 (eg) transition of divalent europium in the hydrides and Deuterides LiMH3 and LiMD3 (M = Sr and Ba). For low doping concentrations, these compounds show extraordinarily well-resolved vibronic fine structures at low temperatures. Besides luminescence emission spectroscopy of the europium-doped compounds, we carried out inelastic neutron scattering (INS) experiments of the europium-free compounds. The phonons coupling to the electronic transition are identified, and a good agreement between the vibronic and the INS data is found. The frequencies of the low-energy acoustic modes do not significantly change upon replacing hydride by deuteride, whereas a decrease by a factor of approximately 2 can be observed for the higher energy optic modes. Furthermore, we compare these experimental results to density functional calculations performed with the Vienna Ab initio Simulation Package. Knowledge of the phon...
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Electron–Phonon Coupling in Luminescent Europium-Doped Hydride Perovskites Studied by Luminescence Spectroscopy, Inelastic Neutron Scattering, and First-Principles Calculations
2018Co-Authors: Gauthier Lefevre, Holger Kohlmann, Alexander Herfurth, Adlane Sayede, Thomas Wylezich, Sacha Welinski, Pedro Duarte Vaz, Stewart F. Parker, Jean François Blach, Philippe GoldnerAbstract:We present a case study on the vibrational coupling of lattice phonons to the electronic 4f7 (8S7/2)–4f65d1 (eg) transition of divalent europium in the hydrides and Deuterides LiMH3 and LiMD3 (M = Sr and Ba). For low doping concentrations, these compounds show extraordinarily well-resolved vibronic fine structures at low temperatures. Besides luminescence emission spectroscopy of the europium-doped compounds, we carried out inelastic neutron scattering (INS) experiments of the europium-free compounds. The phonons coupling to the electronic transition are identified, and a good agreement between the vibronic and the INS data is found. The frequencies of the low-energy acoustic modes do not significantly change upon replacing hydride by deuteride, whereas a decrease by a factor of approximately 2 can be observed for the higher energy optic modes. Furthermore, we compare these experimental results to density functional calculations performed with the Vienna Ab initio Simulation Package. Knowledge of the phonons of a host material is of great importance because phonons have a large influence on the optical properties, such as line widths or luminescence quenching. Hydride-containing host lattices are an ideal model system because 1H can easily be replaced by 2D so that isotope effects can be investigated
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In Situ Hydrogenation of the Zintl Phase SrGe
2017Co-Authors: Henry Auer, Dirk Wallacher, Thomas Christian Hansen, Holger KohlmannAbstract:Hydrides (Deuterides) of the CrB-type Zintl phases AeTt (Ae = alkaline earth; Tt = tetrel) show interesting bonding properties with novel polyanions. In SrGeD4/3–x (γ phase), three zigzag chains of Ge atoms are condensed and terminated by covalently bound D atoms. A combination of in situ techniques (thermal analysis and synchrotron and neutron powder diffraction) revealed the existence of two further hydride (deuteride) phases with lower H (D) content (called α and β phases). Both are structurally related to the parent Zintl phase SrGe and to the ZrNiH structure type containing variable amounts of H (D) in Sr4 tetrahedra. For α-SrGeDy, the highest D content y = 0.29 was found at 575(2) K under 5.0(1) MPa of D2 pressure, and β-SrGeDy shows a homogeneity range of 0.47 < y < 0.63. Upon decomposition of SrGeD4/3–x (γ-SrGeDy), tetrahedral Sr4 voids stay filled, while the Ge-bound D4 site loses D. When reaching the lower D content limit, SrGeD4/3–x (γ phase) with 0.10 < x < 0.17, decomposes to the β phase. All three hydrides (Deuterides) of SrGe show variable H (D) content
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Hydrides of Alkaline Earth–Tetrel (AeTt) Zintl Phases: Covalent Tt–H Bonds from Silicon to Tin
2017Co-Authors: Henry Auer, Thomas Christian Hansen, Robin Guehne, Marko Bertmer, Sebastian Weber, Patrick Wenderoth, Jürgen Haase, Holger KohlmannAbstract:Zintl phases form hydrides either by incorporating hydride anions (interstitial hydrides) or by covalent bonding of H to the polyanion (polyanionic hydrides), which yields a variety of different compositions and bonding situations. Hydrides (Deuterides) of SrGe, BaSi, and BaSn were prepared by hydrogenation (deuteration) of the CrB-type Zintl phases AeTt and characterized by laboratory X-ray, synchrotron, and neutron diffraction, NMR spectroscopy, and quantum-chemical calculations. SrGeD4/3–x and BaSnD4/3–x show condensed boatlike six-membered rings of Tt atoms, formed by joining three of the zigzag chains contained in the Zintl phase. These new polyanionic motifs are terminated by covalently bound H atoms with d(Ge–D) = 1.521(9) Å and d(Sn–D) = 1.858(8) Å. Additional hydride anions are located in Ae4 tetrahedra; thus, the features of both interstitial hydrides and polyanionic hydrides are represented. BaSiD2–x retains the zigzag Si chain as in the parent Zintl phase, but in the hydride (deuteride), it is terminated by H (D) atoms, thus forming a linear (SiD) chain with d(Si–D) = 1.641(5) Å
A Percheronguegan - One of the best experts on this subject based on the ideXlab platform.
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structural and magnetic properties of rfe2dx Deuterides r zr y and x 3 5 studied by means of neutron diffraction and 57fe mossbauer spectroscopy
Journal of Physics: Condensed Matter, 2005Co-Authors: G Wiesinger, V Paulboncour, S M Filipek, I Marchuk, Ch Reichl, A PercherongueganAbstract:The structure of Y Fe2D3.5 at 290 K has been refined in a monoclinic superstructure using synchrotron radiation and neutron diffraction experiments. The evolution of the 57Fe Mossbauer spectra versus temperature for ZrFe2Dx and Y Fe2Dx Deuterides with large deuterium content has been studied. For x = 3.5 both ZrFe2Dx and Y Fe2Dx show an increase of the Fe magnetization compared to the parent intermetallic compound, related to the increase of the cell volume. For Y Fe2Dx the Fe moment decreases to complete disappearance as x increases from 3.5 to 5 due to the stronger influence of the Fe–D bonding compared to the volume increase. The evolution of the isomer shift can be attributed to an almost pure volumetric effect in the case of the Y Fe2 Deuterides, whereas for ZrFe2D3.5 additional D–Fe charge transfer has to be taken into account.
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structural properties of two Deuterides lay2ni9d12 8 and cey2ni9d7 7 determined by neutron powder diffraction and x ray absorption spectroscopy
Journal of Solid State Chemistry, 2004Co-Authors: M Latroche, V Paulboncour, A PercherongueganAbstract:Abstract The crystal structure of two Deuterides RY2Ni9Dx (R=La; x=12.8 and R=Ce; x=7.7) have been investigated by means of neutron powder diffraction and X-ray absorption spectroscopy. The structures are best described in the space group R 3 m . The deuterium location has been determined for both compounds. The nature and the occupancy factors of the different D sites are presented. Comparisons are made between the La-based deuteride and the Ce-one in relation with the crystal structure of the intermetallic compounds. Differences in site occupancies within the RM2 and RM5 building units of the PuNi3-type structure are discussed and heterogeneous mixed valence state is reported for the cerium compound.
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the novel ymn2d6 deuteride synthesized under high pressure of gaseous deuterium
Solid State Communications, 2004Co-Authors: Chienyuan Wang, V Paulboncour, A Percheronguegan, Chiacheng Kang, R S Liu, S M Filipek, Maria Dorogova, I Marchuk, Toshiya Hirata, Hwoshuenn SheuAbstract:Abstract The novel intermetallic deuteride YMn 2 D 6 was synthesized under high deuterium pressure. In order to identify the structure and characterize the magnetic properties of this deuteride the powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Mn X-ray absorption near edge structure (XANES) and magnetization measurement (SQUID) were carried out. The crystal structure, the chemical state of Mn and the magnetic properties of this novel deuteride were examined and discussed. It should be noted that the structure of YMn 2 D 6 ( F -43 m ) differs dramatically from C15 symmetry of the parent material. Such a great rearrangement of the metal lattice due to deuterium absorption is rather exceptional for C15 Laves phase.
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high pressure studies of ymn2 laves phase and its Deuterides
Journal of Alloys and Compounds, 2004Co-Authors: H Sugiura, V Paulboncour, A Percheronguegan, S M Filipek, I Marchuk, T Hirata, Maria DorogovaAbstract:Abstract The C15 Laves phase intermetallic YMn 2 and its Deuterides containing 1.15, 2, 3.4 and 4 deuterium (D) atoms per formula unit (pfu) (the structure of YMn 2 D 4 is rhombohedral whereas other three Deuterides preserve the cubic C15 structure) were compressed up to 31 GPa by using diamond anvil cell (DAC). Parameters of equation of state (EOS) were derived for all phases investigated. The discontinuous change of bulk modulus under high pressure has been revealed for all samples investigated. Two Deuterides, YMn 2 D 1.15 and YMn 2 D 2 , decomposed reversibly under pressure into two phases: poor and enriched in deuterium.
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neutron diffraction study of zrm2dx Deuterides m fe co
Journal of Alloys and Compounds, 2003Co-Authors: V Paulboncour, F Boureevigneron, S M Filipek, I Marchuk, I Jacob, A PercherongueganAbstract:Abstract The structure of ZrFe2 and ZrCo2 Deuterides prepared under very high deuterium pressure has been studied by neutron diffraction (ND) at 10 K. The patterns of both compounds are refined with a mixture of intermetallic compound and deuteride. For ZrFe2Dx, the cell volume increases with 23% and the 2.7 D/f.u. are located randomly in A2B2 sites. The Fe moments order in a ferromagnetic structure and increase from 1.8 to 2.2 μB/Fe upon D absorption. The ZrCo2 deuteride shows a doubling of the cell parameter due to deuterium order of 2 D/f.u. in 7 over 12 A2B2 sites with a cell volume increase of 12%.
V Paulboncour - One of the best experts on this subject based on the ideXlab platform.
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crystal structure of ab 2 laves phase hydrides and Deuterides
2018Co-Authors: V PaulboncourAbstract:In this chapter the synthesis and crystal structure of AB2 laves phase hydrides and Deuterides are discussed in detail.
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crystal structure of the a 6 b 23 phase hydrides and Deuterides
2018Co-Authors: V PaulboncourAbstract:In this chapter the synthesis and crystal structure of A6B23 phase hydrides and Deuterides are discussed in detail
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exafs and xrd investigation of crystal structure in cr doped ymn2 Deuterides
Radiation Physics and Chemistry, 2011Co-Authors: M T Klepka, V Paulboncour, S M Filipek, A Wolska, K Lawniczakjablonska, R Sato, I MarchukAbstract:Abstract Among the number of novel hydrides synthesized recently under high hydrogen pressure from various Laves phases, very specific ones are RMn 2 H 6 (where R=Y, Er, Ho, Dy and Gd) with space group Fm-3m. These hydrides (or Deuterides) can be formed independently on the initial structure (C14 or C15) of their parent RMn 2 compounds. Surprisingly, in contrast to hydrides/Deuterides derived so far from the Laves phases, RMn 2 H 6 compounds are not interstitial but are complex compounds. In order to understand better the role played by Mn in formation of the specific RMn 2 D 6 Deuterides we tested the possibility of manganese substitution by chromium, the element preceding Mn in the 3d series. Two YMn 2− X Cr X alloys (where X =0.1 and 0.2) were submitted to treatment at 100 °C and high deuterium pressure. For X =0.1 the majority (88%) phase was Fm-3m space group whereas for X =0.2 the dominant (around 78%) was deuteride with expanded C15 Laves phase lattice (Fd-3m) like for YMn 2 and the second phase (only 22%) was the Fm-3m. This means that substitution of Mn with chromium by amount higher than X =0.1 makes the formation of Fm-3m single phase increasingly difficult. It was also confirmed that Cr preferably locates in 4a positions of the Fm-3m structure of YMn 2 D 6 , which might be responsible for its destabilization.
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studies of novel Deuterides rmn2d6 r rare earth compressed in dac up to 30 gpa
Journal of Physics: Conference Series, 2008Co-Authors: S M Filipek, V Paulboncour, R S Liu, H Sugiura, R Wierzbicki, Nitin C BagkarAbstract:The exposure of RMn2 (C15 or C14 cubic Laves phase, where R = Y; Dy; Ho or Er) to high deuterium pressure leads to formation of novel, unique YMn2D6, DyMn2D6, HoMn2D6 and ErMn2D6 Deuterides with cubic Fm-3m symmetry. In spite of different structures and molecular volumes of parent RMn2 compounds, the molar volumes of RMn2D6 Deuterides are almost identical. In this paper, we present results of studies on RMn2Dx (where R = Y, Dy, Ho and Er) submitted to compression up to 30 GPa in diamond anvil cell (DAC) combined with energy dispersive X-ray diffraction. The EOS (equation of state) parameters of the above four RMn2D6 samples and YMn2Dx, with x ? 4 are compared. The EOS parameters of YMn2D6 are very similar to those of other RMn2D6 but very different than those of interstitial Deuterides YMn2Dx (x ? 4). The phase transition or segregation was not detected in RMn2D6 up to 30 GPa.
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structural and magnetic properties of rfe2dx Deuterides r zr y and x 3 5 studied by means of neutron diffraction and 57fe mossbauer spectroscopy
Journal of Physics: Condensed Matter, 2005Co-Authors: G Wiesinger, V Paulboncour, S M Filipek, I Marchuk, Ch Reichl, A PercherongueganAbstract:The structure of Y Fe2D3.5 at 290 K has been refined in a monoclinic superstructure using synchrotron radiation and neutron diffraction experiments. The evolution of the 57Fe Mossbauer spectra versus temperature for ZrFe2Dx and Y Fe2Dx Deuterides with large deuterium content has been studied. For x = 3.5 both ZrFe2Dx and Y Fe2Dx show an increase of the Fe magnetization compared to the parent intermetallic compound, related to the increase of the cell volume. For Y Fe2Dx the Fe moment decreases to complete disappearance as x increases from 3.5 to 5 due to the stronger influence of the Fe–D bonding compared to the volume increase. The evolution of the isomer shift can be attributed to an almost pure volumetric effect in the case of the Y Fe2 Deuterides, whereas for ZrFe2D3.5 additional D–Fe charge transfer has to be taken into account.
K Yvon - One of the best experts on this subject based on the ideXlab platform.
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structural and spectroscopic studies on the alkali borohydrides mbh4 m na k rb cs
Journal of Alloys and Compounds, 2004Co-Authors: Guillaume Renaudin, Sandrine Gomes, Hansrudolf Hagemann, L Keller, K YvonAbstract:Alkali borohydrides MBH4 and their Deuterides have been investigated by X-ray and neutron powder diffraction (M = K, Rb, Cs) and by infrared and Raman spectroscopy (M = Na, K, Rb, Cs). At room temperature the compounds crystallize with a cubic high temperature (HT) structure having Fm¯ 3m symmetry in which the [BH4] − complexes are disordered. At low temperature (LT) the potassium compound transforms into a tetragonal low temperature structure having P42/nmc symmetry in which the [BH4] − complexes are ordered such as in the isotypic sodium congener. The B–H distances within the complex as measured on the deuteride at 1.5 K are 1.205(3) A. Indications for a partial ordering in the rubidium and cesium compounds exist but are not sufficient for a full structural characterization. Infrared and Raman spectra at room temperature are fully assigned for both hydrides and Deuterides, including the overtones and combination bands, the Fermi resonance type interactions and the 10 Bt o 11 B splitting due to the presence of natural boron in the samples.
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crystal and magnetic structure of tbnial based Deuterides tbniald0 30 and tbniald1 04 studied by neutron diffraction and synchrotron radiation
Journal of Alloys and Compounds, 1999Co-Authors: B C Hauback, V A Yartys, Helmer Fjellvag, L Palhaugen, K YvonAbstract:Abstract The crystal structure of the two lower Deuterides TbNiAlD0.30 and TbNiAlD1.04 formed by intermetallic TbNiAl have been studied by neutron and synchrotron X-ray powder diffraction at room temperature. In addition, neutron diffraction at low temperature has been used to study the magnetic properties of TbNiAlD0.30. Both Deuterides were prepared by deuterium desorption from the saturated deuteride TbNiAlD1.4. For TbNiAlD0.30, superstructure reflections in the room temperature neutron pattern suggest space group P62c and a doubling of the c-axis [a=7.0433(1), c=7.7826(1) A] relative to the intermetallic compound. Deuterium occupies every second trigonal bipyramidal Tb3Ni2 interstice along c (91% occupancy), and the compound orders antiferromagnetically below TN=42 K. Its magnetic structure at 7 and 28 K has two terbium sublattices, both with the same propagation vector k=(1/2, 1/2, 1), but with significantly different magnetic moments of 8.0(1) and 1.3(1) μB per Tb atom (at 7 K). The structure of TbNiAlD1.04 is described in space group Amm2 [a=3.8257(1), b=12.4668(5), c=7.2964(3) A; orthorhombic distortion b/c=0.986√3]. Three different sites are occupied by deuterium, corresponding to one trigonal bipyramidal Tb3Ni2 type (88% occupancy) and two tetrahedral Tb2NiAl-type interstices (50 and 18% occupancy).
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structure of the high pressure phase γ mgh2 by neutron powder diffraction
Journal of Alloys and Compounds, 1999Co-Authors: M Bortz, B Bertheville, G Bottger, K YvonAbstract:Abstract The high-pressure phase γ-MgH 2 was formed by heating the low-pressure phase α-MgH 2 in a multianvil press at 2 GPa pressure to 1070 K for 120 min and successive rapid quenching. Investigation by X-ray and neutron powder diffraction on the deuteride at ambient conditions revealed that it crystallises with the orthorhombic α-PbO 2 type structure (space group Pbcn, Z=4, a =4.5213(3), b =5.4382(3), c =4.9337(3) A (hydride); a =4.5056(3), b =5.4212(3), c =4.9183(3) A (deuteride) at T =295 K). The deuterium atoms surround magnesium in a distorted octahedral configuration with bond distances Mg–D=1.915(3), 1.943(3) and 2.004(3) A. The rutile structure of α-MgH 2 was re-evaluated.
Kai Sun - One of the best experts on this subject based on the ideXlab platform.
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crystal structure of the tetragonal epsilon phase deuteride of ti 15 at mo alloy determined by neutron diffraction
Journal of Alloys and Compounds, 2009Co-Authors: Kai SunAbstract:The crystal structure of the deuteride of Ti(0.85)Mo(0.15) alloy Ti(0.85)Mo(0.15)D(1.47) is determined by neutron powder diffraction to be a tetragonally distorted fluorite-type structure similar to that of epsilon-phase in Ti-H system. The D concentration and c/a axial ratio of this phase are significantly lower than that in the Ti-H system. The formation of epsilon-phase in the Ti-Mo-H system supports the hypothesis that the electron density change play a role in the delta-epsilon phase transition. Considerable broadening of the reflections is observed in the diffraction patterns. and attributed to the D concentration inhomogeneity and anisotropic microstrain in the lattice of the deuteride. (C) 2009 Elsevier B.V All rights reserved.
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neutron diffraction study of the Deuterides of zr0 9ti0 1mncr laves phase alloy
Physica B-condensed Matter, 2006Co-Authors: Kai Sun, Xiumei Guo, Yuntao Liu, Hongli WangAbstract:The structures of three Deuterides with different D contents for C14-type Laves phase Zr0.9Ti0.1MnCr alloy are studied by neutron and X-ray diffraction. A saturated deuteride containing similar to 3.5 D per mole of alloy is formed at 500 kPa. The structures of the Deuterides are similar to that of ZrMn2D3 with all D atoms in the interstices formed by two Zr/Ti and two Mn/Cr atoms. The lattice constants of a deuteride formed at desorption stage appear to be larger than that of the saturated deuteride with higher D concentration. A solid solution containing similar to 0.1 D per mole of alloys is formed after de-hydrogenation. The remaining D atoms are in the more stable sites, which possess greater atom affinity and larger interstitial size. Strong diffuse scattering apparently due to hydrogen-induced amorphization has been observed in the diffraction patterns of the Deuterides. (c) 2006 Elsevier B.V. All rights reserved.
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neutron diffraction study of the Deuterides of ti mo alloys
Physica B-condensed Matter, 2006Co-Authors: Kai Sun, Xuezhong Yuan, Dongfeng Chen, Cheng GouAbstract:The structures of the Deuterides of seven Ti-Mo alloys with different Mo contents ranging from 5 to 40 at% are studied by neutron diffraction. After deuterization at similar to 150kPa, the saturated Deuterides containing similar to 1.8-1.9 deuterium per alloy atom with a delta-phase titanium hydride type of structure have formed. The lattice constants of the Deuterides decrease consistently with the increase of Mo content. The analysis of the line broadening of the diffraction patterns has revealed the relationship between lattice deformation and the contents of the alloying Mo in the Deuterides. (c) 2006 Elsevier B.V. All rights reserved.
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structure of deuteride of a null matrix ti mo alloy studied by complementation of neutron and x ray powder diffraction
Journal of Alloys and Compounds, 2006Co-Authors: Xianxia Yuan, Suping Liu, Liping Guo, Kai SunAbstract:The detailed structural information of the deuteride of a null matrix Ti-Mo alloy containing 33 at.% of Mo is studied by complementation of the neutron and X-ray powder diffraction techniques. The deuteride containing similar to 1.8 deuterium atoms per alloy atom forms a titanium 8-hydride type of structure with deuterium atoms in the tetrahedral interstitial sites. The line broadening analysis of the deuteride phase suggests that the deuterization of the alloy causes strong lattice deformation effects, and the micro-strain is likely to be dislocation induced. In comparison with the deformation of the host Ti-Mo alloy matrix lattice, a relaxation effect is observed for the deformation of the interstitial deuterium sublattice. (c) 2006 Elsevier B.V. All rights reserved.