The crystal structure of La2Co2O5is determined on the basis of high-resolution powder X-ray diffr... more The crystal structure of La2Co2O5is determined on the basis of high-resolution powder X-ray diffraction and neutron diffraction data. La2Co2O5adopts the brownmillerite-type structure, where single layers of corner-sharing CoO6-octahedra are connected by layers with chains of corner-sharing CoO4-tetrahedra running along [100]. Three alternative descriptions of the crystal structure in space groupsPnma,Imma, andIma2 with slightly different structural distortions and/or atomic disorder are
A new calcium substituted palladium hydride, CaPd 3 H, has been synthesized and the metal structu... more 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 (D0 24 ) type. From a Guinier-Hägg X-ray powder diffraction pattern the unit cell dimensions were determined to be a ϭ 5.8617(2) and c ϭ 9.7793(6) Å. 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.
The thermal decomposition of BaC2O4·3.5H2O and BaC2O4·0.5H2O was investigated using in situ synch... more The thermal decomposition of BaC2O4·3.5H2O and BaC2O4·0.5H2O was investigated using in situ synchrotron X-ray and neutron powder diffraction. The decomposition routes for the barium oxalate hydrates were observed to depend on the applied heating rate. Thermal decomposition of BaC2O4·0.5H2O showed transformation to α-BaC2O4 and to β-BaC2O4 prior to the formation of BaCO3. The decomposition of BaC2O4·3.5H2O showed formation of BaC2O4·0.5H2O
A new class of quaternary complex transition metal hydrides (Na 2 Mg 2 TH 8 (T = Fe, Ru)) have be... more A new class of quaternary complex transition metal hydrides (Na 2 Mg 2 TH 8 (T = Fe, Ru)) have been synthesized and their structures determined by combined synchrotron radiation X-ray and powder neutron diffraction. The compounds can be considered as a link between ionic and complex hydrides in terms of incorporating independently coordinated ionic and covalent hydrogen. These novel isostructural complex transition metal hydrides crystallize in the orthorhombic space group Pbam, where the octahedral complex hydride anion is surrounded by a cubic array of four Mg 2+ and four Na + cations, forming distinct two-dimensional layers. An intriguing feature of these materials is the distorted octahedral coordination of the isolated H À anions by four Na + and two Mg 2+ cations, which form layers between the transition metal containing layers. The vibrational modes of the H À anions and complex hydride anion are independently observed for the first time in a quaternary complex transition metal hydride system by Raman and IR spectroscopy.
Mg and Mg alloys are the one of most studied materials for hydrogen storage due to their high hyd... more Mg and Mg alloys are the one of most studied materials for hydrogen storage due to their high hydrogen capacity (7.6 wt.%), abundance, low cost, low specific energy repeatedly hydriging/dehydriding ability and low environmental impact. Unfortunately the high thermodynamic stability as well as slow kinetics, makes it difficult for practical application. The ternary hydride Mg 2 NiH 4 can store
The thermal decomposition of Mg(AlH 4 ) 2 was studied by in situ synchrotron X-ray diffraction. T... more The thermal decomposition of Mg(AlH 4 ) 2 was studied by in situ synchrotron X-ray diffraction. The reaction proceeds in two steps. The first reaction step involves decomposition of magnesium alanate to magnesium hydride and the solid solution
The large strength-to-weight ratio of titanium makes this element animportant structural componen... more The large strength-to-weight ratio of titanium makes this element animportant structural component in the aerospace industry. The strength and other mechanicalproperties may be further improved by alloying with aluminum to form aluminides, e.g. Ti3Al and TiAl, but at a large loss in ductility. Exposure of the aluminides to hydrogen cancause profound reduction in mechanical stabilities through hydride formation. This paper
... The crystal structure of ScFeO 3 was determined by combined refinements of powder X-ray and n... more ... The crystal structure of ScFeO 3 was determined by combined refinements of powder X-ray and neutron diffraction data. The magnetic behavior is typical of a frustrated system and no long range order prevails at 9 K. Research highlights. ...
The microstructure of LiAlD4 has been studied during the decomposition process using powder X-ray... more The microstructure of LiAlD4 has been studied during the decomposition process using powder X-ray diffraction (PXD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Selected area diffraction (SAD) confirmed the existence of all the decomposed phases presented in the X-ray powder diffraction data. High-resolution transmission electron microscopy confirmed the presence of the LiAlD4 phase before decomposition. After the first
LiMgAlH6 is the intermediate phase when LiMg(AlH4)3 is heated. It contains 9.4wt.% hydrogen, of w... more LiMgAlH6 is the intermediate phase when LiMg(AlH4)3 is heated. It contains 9.4wt.% hydrogen, of which 4.8wt.% is released during the decomposition step to MgH2 and LiH. Deuterated LiMgAlD6 was prepared by heat-treating LiMg(AlD4)3 at 130°C. Powder neutron and synchrotron X-ray diffraction patterns were measured and the structure was refined using the Rietveld technique on both patterns simultaneously. LiMgAlD6 crystallizes in
The structure of LiMg(AlD4)3 was investigated using synchrotron radiation powder X-ray diffractio... more The structure of LiMg(AlD4)3 was investigated using synchrotron radiation powder X-ray diffraction, powder neutron diffraction, and density functional theory atomic simulations. The experimental crystallographic data were refined with the monoclinic P21/c space group and unit cell dimensions: a=8.37113(16)Å, b=8.73910(17)Å, c=14.3012(3)Å and β=124.8308(8)Å. The atomic simulations verified the increased stability of this structure with respect to a wide range of other
NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotro... more NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotron X-ray diffraction in order to unveil the nature of Ti. No crystalline Ti-containing phases were observed after ball milling of NaAlH4 with the additives, neither as a solid solution in NaAlH4 nor as secondary phases. However, after cycling, a high-angle shoulder of Al is observed in the same position with 10% TiCl3 as that with 2% Ti(OBu)4, but with considerably higher intensity, indicating that the shoulder is caused by Ti. After prolonged reabsorption, there is only a small fraction of free Al phase left to react with Na3AlH6, whereas the shoulder caused by Al(1-y)Ti(y) is dominating. The Ti-containing phase causing the shoulder therefore contains less Ti than Al3Ti, and the aluminum in this phase is too strongly bound to react with Na3AlH6 to form NaAlH4. The composition of the Al(1-y)Ti(y) phase is estimated from quantitative phase analysis of powder X-ray diffraction data to be Al(0.85)Ti(0.15). Formation of this phase may explain the reduction of capacity beyond the theoretical reduction from the dead weight of the additive and the reaction between the additive and NaAlH4.
The microstructure of LiAlD 4 with TiCl 3 ‚1/3(AlCl 3 ) and VCl 3 additives has been studied duri... more The microstructure of LiAlD 4 with TiCl 3 ‚1/3(AlCl 3 ) and VCl 3 additives has been studied during different steps of the decomposition process using electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope. Energy filtered transmission electron microscopy was used to show elemental distributions in the samples. The spatial distribution of the additives and the main elements within the alanate particles was examined with a resolution of a few nanometers. The analysis of the electron energy loss spectra reveals the chemical state of Al, O, and the additives. Ti and V do not appear to mix chemically with Al to a significant degree. V was found in high concentration in just a few particles, while Ti is more uniformly distributed. All the samples showed evidence of oxidation despite procedures being adopted to avoid exposing the material to air. The additives are oxidized in all the samples, and Al 2 O 3 forms a thin layer at the surface of the particles. This paper gives a comparison between samples at different stages of the decomposition process using different additives. * Corresponding
We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray po... more We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Ca(BD4)2 shows a variety of structures depending on the synthesis and temperature of the samples. An unknown tetragonal crystal of Ca(BD4)2, the beta phase has been solved from diffraction data measured at 480 K on a sample synthesized by solid-gas mechanochemical reaction by using MgB2 as starting material. Above 400 K, this sample has the particularity to be almost completely into the beta phase of Ca(BD4)2. Seven tetragonal structure candidates gave similar fit of the experimental data. However, combined experimental and ab initio calculations have shown that the best description of the structure is with the space group P4(2)/m based on appropriate size/geometry of the (BD4)tetrahedra, the lowest calculated formation energy, and real positive vibrational energy, indicating a stable structure. At room temperature, this sample consists mainly of the previously reported alpha phase with space group Fddd. In the diffraction data, we have identified weak peaks of a hitherto unsolved structure of an orthorombic gamma phase of Ca(BD4)2. To properly fit the diffraction data used to solve and refine the structure of the beta phase, a preliminary structural model of the gamma phase was used. A second set of diffraction data on a sample synthesized by wet chemical method, where the gamma phase is present in significant amount, allowed us to index this phase and determine the preliminary model with space group Pbca. Ab initio calculations provide formation energies of the alpha phase and beta phase of the same order of magnitude (delta H < or = 0.15 eV). This indicates the possibility of coexistence of these phases at the same thermodynamical conditions.
The crystal structure of La2Co2O5is determined on the basis of high-resolution powder X-ray diffr... more The crystal structure of La2Co2O5is determined on the basis of high-resolution powder X-ray diffraction and neutron diffraction data. La2Co2O5adopts the brownmillerite-type structure, where single layers of corner-sharing CoO6-octahedra are connected by layers with chains of corner-sharing CoO4-tetrahedra running along [100]. Three alternative descriptions of the crystal structure in space groupsPnma,Imma, andIma2 with slightly different structural distortions and/or atomic disorder are
A new calcium substituted palladium hydride, CaPd 3 H, has been synthesized and the metal structu... more 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 (D0 24 ) type. From a Guinier-Hägg X-ray powder diffraction pattern the unit cell dimensions were determined to be a ϭ 5.8617(2) and c ϭ 9.7793(6) Å. 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.
The thermal decomposition of BaC2O4·3.5H2O and BaC2O4·0.5H2O was investigated using in situ synch... more The thermal decomposition of BaC2O4·3.5H2O and BaC2O4·0.5H2O was investigated using in situ synchrotron X-ray and neutron powder diffraction. The decomposition routes for the barium oxalate hydrates were observed to depend on the applied heating rate. Thermal decomposition of BaC2O4·0.5H2O showed transformation to α-BaC2O4 and to β-BaC2O4 prior to the formation of BaCO3. The decomposition of BaC2O4·3.5H2O showed formation of BaC2O4·0.5H2O
A new class of quaternary complex transition metal hydrides (Na 2 Mg 2 TH 8 (T = Fe, Ru)) have be... more A new class of quaternary complex transition metal hydrides (Na 2 Mg 2 TH 8 (T = Fe, Ru)) have been synthesized and their structures determined by combined synchrotron radiation X-ray and powder neutron diffraction. The compounds can be considered as a link between ionic and complex hydrides in terms of incorporating independently coordinated ionic and covalent hydrogen. These novel isostructural complex transition metal hydrides crystallize in the orthorhombic space group Pbam, where the octahedral complex hydride anion is surrounded by a cubic array of four Mg 2+ and four Na + cations, forming distinct two-dimensional layers. An intriguing feature of these materials is the distorted octahedral coordination of the isolated H À anions by four Na + and two Mg 2+ cations, which form layers between the transition metal containing layers. The vibrational modes of the H À anions and complex hydride anion are independently observed for the first time in a quaternary complex transition metal hydride system by Raman and IR spectroscopy.
Mg and Mg alloys are the one of most studied materials for hydrogen storage due to their high hyd... more Mg and Mg alloys are the one of most studied materials for hydrogen storage due to their high hydrogen capacity (7.6 wt.%), abundance, low cost, low specific energy repeatedly hydriging/dehydriding ability and low environmental impact. Unfortunately the high thermodynamic stability as well as slow kinetics, makes it difficult for practical application. The ternary hydride Mg 2 NiH 4 can store
The thermal decomposition of Mg(AlH 4 ) 2 was studied by in situ synchrotron X-ray diffraction. T... more The thermal decomposition of Mg(AlH 4 ) 2 was studied by in situ synchrotron X-ray diffraction. The reaction proceeds in two steps. The first reaction step involves decomposition of magnesium alanate to magnesium hydride and the solid solution
The large strength-to-weight ratio of titanium makes this element animportant structural componen... more The large strength-to-weight ratio of titanium makes this element animportant structural component in the aerospace industry. The strength and other mechanicalproperties may be further improved by alloying with aluminum to form aluminides, e.g. Ti3Al and TiAl, but at a large loss in ductility. Exposure of the aluminides to hydrogen cancause profound reduction in mechanical stabilities through hydride formation. This paper
... The crystal structure of ScFeO 3 was determined by combined refinements of powder X-ray and n... more ... The crystal structure of ScFeO 3 was determined by combined refinements of powder X-ray and neutron diffraction data. The magnetic behavior is typical of a frustrated system and no long range order prevails at 9 K. Research highlights. ...
The microstructure of LiAlD4 has been studied during the decomposition process using powder X-ray... more The microstructure of LiAlD4 has been studied during the decomposition process using powder X-ray diffraction (PXD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Selected area diffraction (SAD) confirmed the existence of all the decomposed phases presented in the X-ray powder diffraction data. High-resolution transmission electron microscopy confirmed the presence of the LiAlD4 phase before decomposition. After the first
LiMgAlH6 is the intermediate phase when LiMg(AlH4)3 is heated. It contains 9.4wt.% hydrogen, of w... more LiMgAlH6 is the intermediate phase when LiMg(AlH4)3 is heated. It contains 9.4wt.% hydrogen, of which 4.8wt.% is released during the decomposition step to MgH2 and LiH. Deuterated LiMgAlD6 was prepared by heat-treating LiMg(AlD4)3 at 130°C. Powder neutron and synchrotron X-ray diffraction patterns were measured and the structure was refined using the Rietveld technique on both patterns simultaneously. LiMgAlD6 crystallizes in
The structure of LiMg(AlD4)3 was investigated using synchrotron radiation powder X-ray diffractio... more The structure of LiMg(AlD4)3 was investigated using synchrotron radiation powder X-ray diffraction, powder neutron diffraction, and density functional theory atomic simulations. The experimental crystallographic data were refined with the monoclinic P21/c space group and unit cell dimensions: a=8.37113(16)Å, b=8.73910(17)Å, c=14.3012(3)Å and β=124.8308(8)Å. The atomic simulations verified the increased stability of this structure with respect to a wide range of other
NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotro... more NaAlH4 samples with Ti additives (TiCl3, TiF3, and Ti(OBu)4) have been investigated by synchrotron X-ray diffraction in order to unveil the nature of Ti. No crystalline Ti-containing phases were observed after ball milling of NaAlH4 with the additives, neither as a solid solution in NaAlH4 nor as secondary phases. However, after cycling, a high-angle shoulder of Al is observed in the same position with 10% TiCl3 as that with 2% Ti(OBu)4, but with considerably higher intensity, indicating that the shoulder is caused by Ti. After prolonged reabsorption, there is only a small fraction of free Al phase left to react with Na3AlH6, whereas the shoulder caused by Al(1-y)Ti(y) is dominating. The Ti-containing phase causing the shoulder therefore contains less Ti than Al3Ti, and the aluminum in this phase is too strongly bound to react with Na3AlH6 to form NaAlH4. The composition of the Al(1-y)Ti(y) phase is estimated from quantitative phase analysis of powder X-ray diffraction data to be Al(0.85)Ti(0.15). Formation of this phase may explain the reduction of capacity beyond the theoretical reduction from the dead weight of the additive and the reaction between the additive and NaAlH4.
The microstructure of LiAlD 4 with TiCl 3 ‚1/3(AlCl 3 ) and VCl 3 additives has been studied duri... more The microstructure of LiAlD 4 with TiCl 3 ‚1/3(AlCl 3 ) and VCl 3 additives has been studied during different steps of the decomposition process using electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope. Energy filtered transmission electron microscopy was used to show elemental distributions in the samples. The spatial distribution of the additives and the main elements within the alanate particles was examined with a resolution of a few nanometers. The analysis of the electron energy loss spectra reveals the chemical state of Al, O, and the additives. Ti and V do not appear to mix chemically with Al to a significant degree. V was found in high concentration in just a few particles, while Ti is more uniformly distributed. All the samples showed evidence of oxidation despite procedures being adopted to avoid exposing the material to air. The additives are oxidized in all the samples, and Al 2 O 3 forms a thin layer at the surface of the particles. This paper gives a comparison between samples at different stages of the decomposition process using different additives. * Corresponding
We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray po... more We have investigated the crystal structure of Ca(BD4)2 by combined synchrotron radiation X-ray powder diffraction, neutron powder diffraction, and ab initio calculations. Ca(BD4)2 shows a variety of structures depending on the synthesis and temperature of the samples. An unknown tetragonal crystal of Ca(BD4)2, the beta phase has been solved from diffraction data measured at 480 K on a sample synthesized by solid-gas mechanochemical reaction by using MgB2 as starting material. Above 400 K, this sample has the particularity to be almost completely into the beta phase of Ca(BD4)2. Seven tetragonal structure candidates gave similar fit of the experimental data. However, combined experimental and ab initio calculations have shown that the best description of the structure is with the space group P4(2)/m based on appropriate size/geometry of the (BD4)tetrahedra, the lowest calculated formation energy, and real positive vibrational energy, indicating a stable structure. At room temperature, this sample consists mainly of the previously reported alpha phase with space group Fddd. In the diffraction data, we have identified weak peaks of a hitherto unsolved structure of an orthorombic gamma phase of Ca(BD4)2. To properly fit the diffraction data used to solve and refine the structure of the beta phase, a preliminary structural model of the gamma phase was used. A second set of diffraction data on a sample synthesized by wet chemical method, where the gamma phase is present in significant amount, allowed us to index this phase and determine the preliminary model with space group Pbca. Ab initio calculations provide formation energies of the alpha phase and beta phase of the same order of magnitude (delta H < or = 0.15 eV). This indicates the possibility of coexistence of these phases at the same thermodynamical conditions.
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Papers by Bjørn Hauback