F. Gingl

New approach for synthesizing Mg-based alloys

Abstract Mg 2 Ni, Mg 2 Cu and MgZn 2 were synthesized by means of ball-milling plus solid-state reactions. Firstly, the mixtures of the two elemental powders, corresponding to the compositions of Mg 2 Ni, Mg 2 Cu and MgZn 2 , were subject to ball-milling for 20 min. Then, they were pressed into pellets and sintered at temperatures below the melting points of the components. X-ray diffraction experiments show that the yields of the desired products are above 97 wt.%, higher than those prepared by the conventional metallurgical method. The hydrogenation properties of the Mg 2 Ni sample synthesized by solid-state reaction are in agreement with the previously published results on alloys prepared by the conventional methods.

Trigonal SrAl2H2: the first Zintl phase hydride

Abstract The title compound and its deuteride were synthesized by hydrogenating/deuterating SrAl 2 at 50 bar H 2 /D 2 pressure and temperatures below 200°C. As found by in situ X-ray powder diffraction, the hydrogenation of SrAl 2 proceeds in three steps, with SrAl 2 H 2 as the first product. SrAl 2 H 2 and SrAl 2 D 2 were characterized by X-ray and neutron powder diffraction. They crystallize with a new trigonal structure in space group P3m1 (164), cell parameters: a =4.5283(1) A, c =4.7215(2) A (hydride), a =4.5253(1) A, c =4.7214(2) A (deuteride), Z =1. The main feature of this structure is a two-dimensional polymer Zintl anion, ∞ 2 [AlH − ] 2 n , in which one H atom is covalently bonded to each Al atom. SrAl 2 H 2 is the first example of a Zintl phase hydride, i.e., the first Zintl phase in which hydrogen atoms are a part of the Zintl anion.

In situ X-ray diffraction study of hydrogen-induced phase decomposition in LaMg12 and La2Mg17

Abstract In situ X-ray diffraction (XRD) shows that LaMg 12 and La 2 Mg 17 are thermally stable under argon upon heating to 330°C, while under hydrogen they decompose to LaH 3 and MgH 2 at about 290 and 270°C, respectively. The decomposition is believed to result from the large difference in enthalpy between the parent compounds and the resultants. Prior to the decomposition, the lattice parameters of LaMg 12 and La 2 Mg 17 do not change, indicating that hydrogen does not dissolve into them to form solid solution of LaMg 12 H x and La 2 Mg 17 H x . The enhanced mobility of La and/or Mg was observed in the presence of hydrogen, which might be related to the formation of the copious vacancy.

Strontium magnesium tetrahydride (SrMgH4) : a new ternary alkaline earth hydride

Abstract Strontium magnesium tetrahydride (SrMgH 4 ) and its deuteride (SrMgD 4 ) were prepared from SrMg alloy at 765 K under a hydrogen (deuterium) pressure of 95 bar and characterized by X-ray and neutron powder diffraction. The compound crystallizes with the BaZnF 4 structure type, with the space group Cmc2 1 and with the following lattice parameters at 295 K: a=3.9661(3) A , b=13.685(1) A , c=5.5755(6) A (deuteride) and Z =4. It contains four symmetry-independent deuterium sites having tetrahedral (D(1), D(2) [3Sr, Mgl, D(4) [2Sr, 2Mg]) and T-shaped (D(3) [Sr, 2Mg]) metal coordinations. The metal-deuterium bond distances range from 1.87 to 2.06 A (Mg-D) and from 2.43 to 2.82 A (Sr-D).

Synthesis and crystal structure of tetragonal LnMg2H7 (Ln=La, Ce), two Laves phase hydride derivatives having ordered hydrogen distribution

Abstract LaMg 2 H 7 , CeMg 2 H 7 and their deuterides were synthesized by hydrogenation (deuteration) of binary LnMg 2 at 373 K (Ln=La) and 423 K (Ln=Ce) and 100 bar hydrogen (deuterium) pressure and characterized by X-ray and neutron powder diffraction at room temperature. Their metal substructure represents a new tetragonal distortion variant of the cubic C15 Laves phase structure, space group P 4 1 2 1 2 (No. 92); cell parameters for LaMg 2 H 7 : a =6.4054(2) A, c =9.5994(3) A; LaMg 2 D 7 : a =6.3900(2) A, c =9.5782(4) A; CeMg 2 H 7 : a =6.3663(3) A, c =9.5226(5) A; CeMg 2 D 7 : a =6.3501(3) A, c =9.4957(5) A; Z =4. The hydrogen (deuterium) distribution consists of four symmetry independent, fully occupied sites having triangular [Ln 2 Mg] and tetrahedral [Ln 2 Mg 2 ] and [Mg 4 ] metal coordinations with distances in the range La–D=2.39–2.55 A; Ce–D=2.36–2.51 A; Mg–D=1.92–2.13 A (La), 1.91–2.18 A (Ce). The hydrogen-to-metal ratio, H/M=7/3, is the highest reported so far for Laves phase hydride derivatives.

Tetracalcium trimagnesium tetradecahydride, Ca4Mg3H14 : the first ternary alkaline earth hydride

Abstract The title compound and its deuteride, Ca4Mg3D14, were prepared from CaMg alloy at 410(10) °C (deuteride: 458(8) °C) under 53(3) bar hydrogen (95(5) bar deuterium) pressure and characterized by X-ray and neutron powder diffraction. The compound crystallizes with a new hexagonal structure type (space group P62m (No. 189); lattice parameters at 20 °C: a = 6.3056(2) A , c = 6.8820(2) A ( hydride ) , a = 6.2902(2) A , c = 6.8540(3) A ( deuteride ) , Z = 1) which contains an ordered array of four symmetry-independent deuterium atoms having respectively tetrahedral (D1:[3Ca, 1Mg]; D2: [4Ca]), trigonal bipyramidal (D3: [2Ca, 3Mg]) and triangular (D4: [3Mg]) metal coordinations. The metal-deuterium bond distances range from 1.85 to 2.44 A (Mg-D) and from 2.29 to 2.48 A (Ca-D).

Monoclinic Sr2Mg3H10 with Ba2Ni3F10-type structure

Abstract Sr2Mg3H10 and its deuteride were prepared from SrMg2 alloy at 700 K under 75 bar hydrogen (65 bar deuterium) pressure and characterized by X-ray and neutron powder diffraction. They crystallize with the monoclinic Ba2Ni3F10 structure type in space group C2 m (No. 12), with the following cell parameters at 295 K: a = 17.586(5) A , b = 5.742(2) A , c = 7.491(2) A , β = 111.51(2)°, V = 703.8(2) A 3 ( hydride ); a = 17.539(4) A , b = 5.730(1), A , c = 7.480(2) A , β = 111.48(2)°, V = 699.5(2) A 3 ( deuteride ); Z = 4 . The metal-deuterium bond distances range from 1.81 to 2.14 A (MgD) and from 2.49 to 2.96 A (SrD).

Synthesis and crystal structure of BaMgH4: A centrosymmetric variant of SrMgH4

Abstract BaMgH4 and its deuteride were synthesized by sintering 1:1 mixtures of BaH2 (BaD2) and Mg powder at 873 K and 200 bar hydrogen (deuterium) pressure for 10 days, and these were characterized by X-ray and neutron powder diffraction. They crystallize with the orthorhombic LaNiD4 structure type, space group Cmcm (No. 63), cell parameters at 295 K, hydride: a=4.2109(2) A , b=13.7672(8) A , c=5.6984(3) A , V=330.35(3) A 3 ; deuteride; a=4.1992(1) A , b=13.7374(5) A , c=5.6852(2) A , V=327.96(2) A 3 ; Z=4 . The structure contains one barium and one magnesium site having 13 (Ba) and 6 (Mg) deuterium neighbors and three deuterium sites which are four-, five- and sixfold coordinated, respectively. The metal-deuterium distances are in the range 2.66–3.16 A (Ba-D) and 1.87–2.11 A (Mg-D). The shortest D-D distance is 2.59 A.

ERSTE BESTIMMUNG VON EU-H-ABSTANDEN DURCH NEUTRONENBEUGUNG AN DEN NEUARTIGEN HYDRIDEN EUMG2H6 UND EUMGH4

TrotzderhohenNeutronenabsorption von naturlichem Europium konnten die Kristallstrukturen zweier Eu-Hydride aus Pulverdaten abgeleitet werden. EuMg2D6 kristallisiert in einem neuen AB2X6-Strukturtyp (siehe Bild), EuMgD4 ist isotyp zu BaZnF4. Die mittleren Eu-D-Abstande betragen 258 bzw. 253 pm.

The First Determination of Eu−H Distances by Neutron Diffraction on the Novel Hydrides EuMg2H6 and EuMgH4

Despitethehighneutronabsorption of natural europium, the crystal structures of two Eu hydrides could be solved from powder diffraction data. EuMg2D6 crystallizes in a novel AB2X6 structure type (see picture), EuMgD4 is isotypic to BaZnF4. The mean Eu−D distances are 258 and 253 pm, respectively.