Karim Kadir

Synthesis and structure determination of a new series of hydrogen storage alloys; RMg2Ni9 (R=La, Ce, Pr, Nd, Sm and Gd) built from MgNi2 Laves-type layers alternating with AB5 layers

Abstract A number of new ternary magnesium based alloys, RMg2Ni9 (where R=La, Ce, Pr, Nd, Sm and Gd), have been synthesized by reacting a mixture of MgNi2 with RNi5 intermetallic compounds or by direct combination of the elements in the atomic ratio R:Mg:Ni=1:2:9. The crystal structure, determined by Guinier-Hagg X-ray powder diffraction, is related to the hexagonal PuNi3 type. All interatomic distances are close to the corresponding ones in (C15) MgCu2, (C14) MgZn2, (C36) MgNi2, RNi3 and RNi5 of metallic-type bonding.

Structural investigation and hydrogen storage capacity of LaMg2Ni9 and (La0.65Ca0.35)(Mg1.32Ca0.68)Ni9 of the AB2C9 type structure

Abstract A new quaternary magnesium based alloy (La 0.65 Ca 0.35 )(Mg 1.32 Ca 0.68 )Ni 9 and its hydride have been synthesized and their crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compound has a hexagonal structure and is isostructural with LaMg 2 Ni 9 (AB 2 C 9 type), in which Ca partially occupies both A and B sites. The hydrogen absorption/desorption properties were determined by pressure–composition isotherms and compared with LaMg 2 Ni 9 . (La 0.65 Ca 0.35 )(Mg 1.32 Ca 0.68 )Ni 9 absorbs ∼1.87 wt.% H 2 at ∼3.3 MPa H 2 and 283 K.

Structural investigation and hydrogen capacity of CaMg2Ni9: a new phase in the AB2C9 system isostructural with LaMg2Ni9

Abstract A new ternary magnesium-based alloy CaMg 2 Ni 9 has been synthesized, and its crystal structure was determined by Guinier–Hagg X-ray and neutron powder diffraction. The compound has a hexagonal structure and is isostructural with LaMg 2 Ni 9 type, with Ca at the La atom site. The hydrogen absorption/desorption properties have been determined by thermal analysis and pressure–composition isotherms. The electrochemical properties of the alloy were also examined.

Structural investigation and hydrogen capacity of YMg2Ni9 and (Y0.5Ca0.5)(MgCa)Ni9: new phases in the AB2C9 system isostructural with LaMg2Ni9

New ternary magnesium-based alloys, YMg2Ni9 and (Y0.5Ca0.5)(MgCa)Ni9 have been synthesized and their crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compounds are a hexagonal and isostructural with LaMg2Ni9 (AB2C9 type), in which Y is uniquely at the A site as in YMg2Ni9, and Ca partially occupies both A and B sites. The hydrogen absorption/desorption properties were determined by pressure–composition isotherms. YMg2Ni9 does not absorb hydrogen, whereas (Y0.5Ca0.5)(MgCa)Ni9 absorbs ∼2 wt.% H2 at ∼3.3 MPa and 263 K.

Investigation of the perovskite related structures of NaMgH3, NaMgF3 and Na3AlH6

Abstract Two perovskite related metal hydrides, NaMgH 3 and Na 3 AlH 6 were structurally investigated using powder diffraction techniques. Single crystal X-ray data was also used to for the first time confirm that the structure of NaMgF 3 is analogous to the orthorombically distorted perovskite structure of GdFeO 3 space group Pnma (no. 62) . Looking for new ternary hydrides in the NaH–MgH 2 system, the only new compound found was NaMgH 3 which is isotypic with NaMgF 3 . The positions of the D atoms in Na 3 AlD 6 , isotypic with the low temperature phase of Na 3 AlF 6 , space group P2 1 /n (no. 14), could for the first time be determined from neutron diffraction data. The degree of distortion was discussed from the point of bonding distances and angles in the octahedra of the hydrides and fluorides. In the case of NaMgH 3 and NaMgF 3 , the angles of which the octahedra are rotated ( φ ) and atomic coordinates were calculated. Both NaMgH 3 and Na 3 AlH 6 appear to be less tilted but more deformed than their corresponding fluorides.

Structural determination of AMgNi4 (where A=Ca, La, Ce, Pr, Nd and Y) in the AuBe5 type structure

Abstract A number of new ternary magnesium based alloys AMgNi 4 (where A=Ca, La, Ce, Pr, Nd, and Y) have been synthesized by direct combination of the elements in the atomic ratio A:Mg:Ni=1:1:4. The crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compounds have a cubic SnMgCu 4 (AuBe 5 type) structure, which is related to the (C 15 ) MgCu 2 structure. All interatomic distances indicate metallic-type bonding.

The crystal and electronic structure of CaPd3H

Abstract A new calcium substituted palladium hydride, CaPd 3 H, has been synthesized and the metal structure was found to be of the Ni 3 Ti ( D 0 24 ) type. From a Guinier-Hagg X-ray powder diffraction pattern the unit cell dimensions were determined to be a = 5.8617(2) and c = 9.7793(6) A. Resistance measurements did not reveal any superconducting transition, but the alloy has metallic character. From considerations of bonding distances in the binary hydrides, the hydrogen atoms are restricted to the octahedral site coordinated by six palladium atoms. The experimental results were confirmed by theoretical calculations on the electronic structure, using the LMTO method. The d -electron bands are filled at the CaPd 3 H composition, thus limiting the hydrogen occupancy to only one H atom per formula unit.

Hydrogen behavior in the La-Mg-Cu system

Abstract A new hexagonal intermetallic phase has been detected in a LaMg 2 Cu 2 preparation, which absorbs large quantities of hydrogen (∼2.4 wt.%). The dissociation pressure of the hydride reaches nearly ∼0.4 atmosphere at 170°C. The hydrogen absorption/desorption properties have been determined by thermal analysis and pressure–composition isotherms.

Ba3Ir2H12, a new ternary hydride containing octahedral [IrH6]3 - complex anions

Abstract A new ternary hydride, Ba 3 Ir 2 H 12 , has been synthesized by reacting a mixture of BaH 2 and iridium powders in a hydrogen atmosphere. The crystal structure was determined by combining Guinier-Hagg X-ray powder diffraction and neutron diffraction data from a deuterated compound. The structure was refined (space group, P-3m1 ; a = 5.4865(3) A and c = 8.8459(10) A ; Z = 1 ). The unit cell contains two slightly distorted [IrH 6 ] 3− octahedra which form a La 2 O 3 -type structure with the three Ba 2+ counterions. Two different Ir-H bond lengths were refined with neutron diffraction data from Ba 3 Ir 2 D 12 : 1.60(1) A and 1.77(2) A.

Investigation of Counterion Influence on an Octahedral IrH6-Complex in the Solid State Hydrides AAeIrH6 (A = Na, K and Ae = Ca, Sr, Ba, and Eu) with a New Structure Type

A number of new quaternary iridium based hydrides and deuterides AAeIrH/D(6) (where A = Na and K; Ae = Ca, Ba, Sr, and Eu) have been synthesized by direct combination of the alkali, alkaline earth or europium binary hydrides/deuterides and iridium powder. The crystal structures were determined by Guinier-Hägg X-ray and neutron powder diffraction and a new cubic structure type was found. The structure is described in space group F43m, but related to the K(2)PtCl(6) type structure. The new structure can be described as consisting of cubes of A(+) and Ae(2+) ions, where the A(+) and Ae(2+) ions alternates so that they occupy opposite corners in the cube. Every second cube contains a regular octahedral [Ir(III)H(6)](-3)-complex and the adjacent is empty. Solid-state IR spectroscopy was used to determine the Ir-allowed stretching and bending frequencies for the [Ir(III)H(6)](-3) complex with different counterions. These were also compared with the corresponding stretching frequencies for Fe(II)H(6), Ru(II)H(6), Os(II)H(6), and Ir(II)H(5) complexes in similar solid state hydrides, which increased when going from Fe through Ru, Os to Ir. The frequencies scaled almost linearly with the inverse of size of the cube surrounding the complexes but showed no significant dependence of the formal oxidation state or the experimentally obtained Ir-D distances. However, this was mainly because of difficulties in obtaining enough accurate atomic positions. The ab initio DFT calculations could reproduce the stretching frequencies within a few 10 cm(-1), indicating that experimental vibrational frequencies offer a sensitive test of DFT results.