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| 3. |
- Denys, R. V., et al.
(författare)
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Crystal chemistry and thermodynamic properties of anisotropic Ce2Ni7H4.7 hydride
- 2007
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 180:9, s. 2566-2576
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Tidskriftsartikel (refereegranskat)abstract
- A new intermetallic deuteride Ce2Ni7D4.7 with an anomalous volume expansion has been studied. Its structure was solved on the basis of in situ neutron diffraction data. Expansion proceeds along the c-axis and within the CeNi2 slabs only. All D atoms are located inside these slabs and on the border between CeNi2 and CeNi5. Ordering of D atoms in the bulk of CeNi2 is accompanied by substantial deformation of these slabs thus lowering the hexagonal symmetry to orthorhombic [space group Pmcn (No. 62); a = 4.9251(3) angstrom b = 8.4933(4) angstrom, c = 29.773(1) angstrom]. Inside the CeNi2 layer the hydrogen sublattice is completely ordered; all D-D distances exceed 2.0 angstrom Local coordination of Ni by D inside the CeNi, blocks is of "open", saddle-like type. Hydrogen ordering is mainly determined by Ce-H and H-H interactions. The press ure-composition-temperature measurements yielded the following thermodynamic parameters of the formation of the hydride: Delta H = -22.4 kJ/MOl(H), Delta S = -59.9 J/(K mol(H)).
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| 4. |
- Denys, R. V., et al.
(författare)
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Mg substitution effect on the hydrogenation behaviour, thermodynamic and structural properties of the La2Ni7-H(D)(2) system
- 2008
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 181:4, s. 812-821
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Tidskriftsartikel (refereegranskat)abstract
- The present work is focused on studies of the influence of magnesium on the hydrogenation behaviour of the (La,Mg)(2)Ni-7 alloys. Substitution of La in La2Ni7 by Mg to form La1.5Mg0.5Ni7 preserves the initial Ce2Ni7 type of the hexagonal P6(3)/mmc structure and leads to contraction of the unit cell. The system La1.5Mg0.5Ni7-H2 (D-2) was studied using in situ synchrotron X-ray and neutron powder diffraction in H-2/D-2 gas and pressure-composition-temperature measurements. La replacement by Mg was found to proceed in an ordered way, only within the Laves-type parts of the hybrid crystal structure, yielding formation of LaMgNi4 slabs with statistic and equal occupation of one site by La and Mg atoms. Mg alters structural features of the hydrogenation process. Instead of a strong unilateral anisotropic expansion which takes place on hydrogenation of La2Ni7, the unit cell of La1.5Mg0.5Ni7D9.1 is formed by nearly equal hydrogen-induced expansions proceeding in the basal plane (Delta a/a = 7.37%) and along [001] (Delta c/c = 9.67%). In contrast with La2Ni7D6.5 where only LaNi2 layers absorb hydrogen atoms, in La1.5Mg0.5Ni7D9.1 both LaNi5 and LaMgNi4 layers become occupied. Nine types of sites were found to be filled by D in total, including tetrahedral (La,Mg)(2)Ni-2, (La,Mg)Ni-3, Ni-4, tetragonal pyramidal La2Ni3 and trigonal bipyramidal (La,Mg)(3)Ni-2 interstices. The hydrogen sublattice around the La/Mg site shows formation of two co-ordination spheres of D atoms: an octahedron MgD6 and a 16-vertex polyhedron LaD16 around La. The interatomic distances are in the following ranges: La-D (2.28-2.71), Mg-D (2.02-2.08), Ni-D (1.48-1.86 angstrom). All D-D distances exceed 1.9 angstrom. Thermodynamic PCT studies yielded the following values for the Delta H and Delta S of hydrogenation/decomposition; Delta H-H = -15.7 +/- 0.9 kJ (mol(H))(-1) and Delta S-H = -46.0 +/- 3.7 J (K mol(H))(-1) for H-2 absorption, and Delta H-H = 16.8 +/- 0.4 kJ (mol(H))(-1) and Delta S-H = 48.1 +/- 1.5 J (K mol(H))(-1) for H-2 desorption.
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- Maletka, K, et al.
(författare)
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Phase transitions in the ionic conductor Li2UBr6 studied by neutron diffraction
- 1998
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Ingår i: SOLID STATE IONICS. - : ELSEVIER SCIENCE BV. ; 106:1-2
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The crystal structure of the Li2UBr6 ionic conductor has been studied as a function of the temperature by powder neutron diffraction. The room and high temperature structures have been determined. At 300 K the compound crystallises in a trigonal unit cel
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- Wannberg A, Mellergård A, Zetterström P, Delaplane R, Grönros M, Karlsson L-E, McGreevy R L
(författare)
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SLAD: A neutron diffractometer for the study of disordered materials
- 1999
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Ingår i: Journal of Neutron Research. - : Overseas Publisher Association. ; 8, s. 133-154
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Tidskriftsartikel (refereegranskat)abstract
- The Studsvik Liquid and Amorpous materials Diffractometer (SLAD)is a neutron diffractometer designed for measurements of the structure factor of liquids, glasses and amorphous materials, for total (i.e. Bragg and diffuse) scattering measurements from powd
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| 8. |
- Cong, DY, et al.
(författare)
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Crystal structures and textures of hot forged Ni48Mn30Ga22 alloy investigated by neutron diffraction technique
- 2005
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Ingår i: Materials Science and Technology. - 0267-0836 .- 1743-2847. ; 21:12, s. 1412-1416
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Tidskriftsartikel (refereegranskat)abstract
- A ferromagnetic shape memory alloy of Ni48Mn30Ga22 prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni48Mn30Ga22 has a cubic L2(1) Heusler structure at room temperature, the same as that in the stoichiometric Ni2MnGa. When cooled to 243 K, the Ni48Mn30Ga22 alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni-Mn-Ga alloys with higher martensitic transformation temperatures.
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| 9. |
- Cong, D. Y., et al.
(författare)
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Neutron diffraction study on crystal structure and phase transformation in Ni-Mn-Ga ferromagnetic shape memory alloys
- 2007
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Ingår i: Powder Diffraction. - : Cambridge University Press (CUP). - 0885-7156 .- 1945-7413. ; 22:4, s. 307-311
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Tidskriftsartikel (refereegranskat)abstract
- Crystal structure and phase transformation behaviors in two Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) with compositions of Ni48Mn30Ga22 and Ni53Mn25Ga22 (at. %) as a function of temperature were investigated by in situ neutron diffraction experiments. Neutron diffraction technique proves to be highly efficient in characterizing structural transformation in Ni-Mn-Ga FSMAs, which consist of nearby elements in the periodic table. Our neutron results show that Ni48Mn30Ga22 has a cubic, L-21 Heusler structure from 373 to 293 K. Its crystal structure changes into a seven-layered orthorhombic martensitic structure when cooled to 243 K, and no further transformation is observed upon cooling to 19 K. Neutron diffraction results also show that Ni53Mn25Ga22 has a tetragonal 14/mmm martensitic structure from 20 to 403 K. A pre-transformation around room temperature is observed from an abrupt jump in unit-cell volume of Ni53Mn25Ga22, which corresponds with an endothermic peak detected in a heated DSC curve.
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