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We present an experimental and theoretical study of the 3d core level spectra along the pnicitides YbN, YbP and YbAs and determine the degree of valence mixing as a function of anion electronegativity. The experimental spectra are obtained using SiKα radiation (hν = 1740 eV). They show on the low binding energy side of the dominating 3d9 4f13 multiplets a weak 3d9 4f14 doublet. The theoretical lineshapes and satellite structures are obtained from a combination of many body techniques due to Gunnarsson and Schoenhammer [1] and standard atomic calculations in intermediate coupling.

Metallic CeH2.7 shows a sizably increased electronic specific heat of γ=100 mJ/mol·K2, compared to γ=0.04 mJ/mol·K2 in LaH2.7 at low tempratures, which could qualify it as another heavy electron system. μSR Knight shift and relaxation studies were started on a powderous CeH2.7 sample in order to test this possibility further. It is found that the relaxation rate λT depends strongly on the applied field strength. These values indicate that the relaxation must be of electronic origin. Strong irreproducibilities at low temperature point to pronounced hysteretic features, which might be related to structural changes. The Knight shift shows a shallow peak around 150 K but no conspicious increase at low temperatures.

Using photoelectron spectroscopy we have observed a reversible surface semiconductor-metal transition in hydrides of light and heavy rare earth metals at low temperatures. The reversible diffusion of hydrogen from octahedral-like surface sites into the bulk is thought to push RE 5d states from the hydrogen bonding band back to the conduction band, producing a metallic surface dihydride.

XPS spectra are presented from films of different stoichiometry: HfN1.0 made by CVD and reactive sputtering and HfN1.09 made by ion plating. They support the existing theoretical calculations where the valence band comprises a strong Hf 5d band immediately below EF and a band of mainly N 2p character some 6 eV below EF. The core levels are shifted to larger binding energies by about 1.5 eV indicating electron transfer from hafnium to nitrogen. The effect of substoichiometry on the spectra is very small.

We analysed the valence band and the 3d and 4d core levels of LaH x ( x = 0, 2.2, 2.9) and CeH x ( x = 0, 2.1, 2.9) using X-ray photoelectron spectroscopy. A hydrogen-induced band around 5 eV is observed in all the hydrides. The density of states at E F is considerably reduced in the dihydrides and vanishes completely in the trihydrides in agreement with the transition from metallic to non-metallic behaviour. The cerium 4f level appears at 2 eV and is separated from the hydrogen-induced band for both cerium hydrides. The character and occupancy of the 4f levels of cerium is almost conserved in the hydrides as is confirmed by measurements of the magnetic susceptibility. The 3d core levels are shifted by 1.3 eV (LaH 2.2 ), 2.9 eV (LaH 2.9 ), 1.9 eV (CeH 2.1 ) and 2.1 eV (CeH 2.9 ) and exhibit intense satellites on the low binding energy side.

The core levels and valence bands of Y, YH2.1, and YH3 have been studied using X-ray photoemission spectroscopy. For YH2.1 and YH3, hydrogen-induced states appear at binding energies of about 6 eV. YH2.1 shows emission at the Fermi level and the core-level spectra show highly asymmetric lineshape with shoulders at the high-binding-energy side of the main peaks. For YH3, emission at the Fermi level is weak and the core-levels are nearly symmetric, consistent with a semiconductor or a semimetal. The main peaks of the core levels shift to higher binding energies from Y to YH2.1 to YH3. Taking into account different core-hole screening mechanisms in these materials, however, a charge transfer from Y to H is evident in YH2, but no clear further Y to H charge transfer is seen in going from YH2 to YH3. Importance of the Y 5sp-H 1s bond is suggested from the valence-band spectra.

Investigations of LaNi5 by means of photoemission spectroscopy, Auger electron spectroscopy and measurements' of the magnetic susceptibility and magnetization show that in a surface layer La diffuses to the surface and metallic Ni precipitations are formed. This surface segregation is enhanced by the presence of oxygen. The segregation continues with each cycle of hydrogenation. This represents a self restoring mechanism of the active surface, since the highly reactive La oxidizes and keeps the Ni metallic. Dissociative adsorption of H2 then occurs at the Ni precipitations.

Recent experimental results on the electronic structure of hydrides of palladium, the rare earths, niobium and magnesium, of the intermetallic compounds LaNi 5 , FeTi and Mg 2 Ni, of the zirconium-based Laves phase compounds and of a few glassy metals are reviewed and compared with results of band structure calculations. The review focuses on results obtained by photoelectron and X-ray spectroscopy methods. Emphasis is placed on missing data to stimulate further investigations.

The surface properties of ZrMn2 and the electronic structure of ZrMn2 hydride were studied by photoelectron spectroscopy. Surface segregation with the preferential oxidation of Mn and not Zr is found to account for the readiness of hydrogen absorption. In ZrMn2 hydride a new hydrogen induced band is formed 6.5 eV below EF. The Zr 3d core levels are shifted to 0.5 eV larger binding energy.

We measured the magnetic susceptibility x as a function of field and temperature for the intermetallic compounds LaNi5, FeTi and Mg2Ni in the form of bulk material and of activated powder in the hydrogenated and dehydrogenated states. LaNi5, FeTi and Mg2Ni are Pauli paramagnets with bulk susceptibilities of 4.6 × 10−6, 3.4 × 10−6 and 0.9 × 10−6 emu g−1 respectively. The three compounds show segregation of lanthanum, titanium and magnesium respectively in a surface layer and the formation of ferromagnetic particles of nickel or iron. Because the bulk is only weakly magnetic and the specific surface area of the powders is large, the surface precipitates of nickel and iron dominate the magnetism of the powders. We checked these surface decomposition effects by measuring the Curie temperature of the precipitates and found the Curie temperatures of nickel in LaNi5 and Mg2Ni powders and that of iron in FeTi powder. The nickel precipitates are superparamagnetic at room temperature and ferromagnetic at 4.2 K. By fitting the magnetization curve with the Langevin function we calculated the size of the superparamagnetic nickel and iron precipitates (6000 nickel atoms in LaNi5, 2000 iron atoms in FeTi). Hydrogenation reduces the bulk susceptibility of LaNi5, FeTi and Mg2Ni.

X-ray and neutron diffraction experiments performed on Mg2Ni(H,D)x (0 ⩽ x ⩽ 3.9) confirmed the existence of a structural phase transformation at about 235 °C. The high temperature phase (a = 6.49 A, space group Fm3m) has an antifluorite-type metal structure in which the deuterium atoms surround the nickel atoms octahedrally in a disordered manner (D−Ni =1.47 A, D−Mg = 2.30 A). Refined atomic parameters of Mg2Ni as well as absorption and desorption isotherms for the deutende and hydride phases are reported.

We report on zero and transverse fieldμSR measurements in LaNi5H6 and inβ-PdHx (x=0.70 and 0.75) between 16 K and room temperature. Theμ+-depolarization is predominantly caused by the spread in nuclear dipole fields from the protons. Motional averaging is caused by the combined motion of protons and theμ+. The results are quite unexpected and point toμ+-trapping within regions of largely immobile hydrogen configurations or to a highly correlatedμ+-proton diffusion. In LaNi5H6 a linear change of the second moment with temperature between 20 K and 120 K is indicated.

This paper presents experimental evidence that it is possible to use a cathodic charge to store hydrogen on compounds such as LaNi 5 . Using an alkaline medium (KOH 5N) in an unpressurized system at 20°C, the mass capacity was found to be approximately 330 mAH/g (5H/mol LaNi 5 ). Comparison of these results with the solid-gas isotherms indicated that the hydrogen is held in a non-equilibrium state. The influence of temperature, stoichiometry and substitution in the LaNi 5 on the capacity are presented.

The orientation dependence of the inhomogeneously broadened μSR line width has been measured in a single crystal α′-PdH0.74 sample between 20 and 150 K. Protons and muon are thought to occupy octahedral interstitial sites in the Pd lattice. A good fit to the data is only obtained assuming a decrease in the proton occupancy of the octahedral sites nearest to the μ+ with increasing temperature. The proton occupancy of the remaining octahedral sites at all temperatures as well as the occupancy of the proton sites nearest to the μ+ at 20 K is compatible with the bulk nominal hydrogen concentration x=0.74.

The effect of oxygen and hydrogen on the surface segretation of amorphous and crystalline alloys of Zr were analyzed by means of AES, XPS, and UPS. Amorphous Cu 70 Zr 30 alloys with high oxygen content showed a very pronounced unexpected Cu enrichment at the surface after annealing at 473 K in H 2 atmosphere.

Hydrogen is stored atomically in metal hydrides. Dissociative chemisorption and associative desorption are therefore important steps in the hydrogen absorption and desorption processes. We summarize the theoretical and experimental knowledge of hydrogen chemisorption on clean and precovered metal surfaces and correlate it with the techniques for preparing metal hydrides. At the surface of hydride-forming intermetallics, precipitates of d metals and a metallic subsurface are produced by surface segregation and decomposition. The subsurface and the precipitates are able to dissociate H2. Our recent work on the surface analysis of LaNi5, FeTi, Mg2Ni and ErFe2 is reviewed.

Zero- and transverse field muon (μ+) spin rotation measurements were performed in LaNi5H6 and PdHx (0.59 ⩽ x ⩽ 0.86) between 16 K and room temperature. The μ+ depolarization is due to the spread in nuclear dipole fields originating predominantly from the protons. Motional averaging is caused by the combined motion of the protons and the β+. The results show a surprisingly low correlation rate 1 τ c which indicates highly correlated μ+-proton diffusion or μ+ trapping within regions of largely immobile hydrogen configurations. μ+ trapping or a localized μ+ jump mode could be considered in LaNi5H6 where a linear decrease in the second moment with temperature between 20 and 120 K was measured in contrast with the unchanged relaxation observed by proton magnetic resonance.

XPS analysis of LaH3 shows that the conduction band of the La metal disappears and that a new hydrogen induced band is formed 5.8 eV below EF. The La 3d core levels of LaH3 are split into two peaks with about 1 3 of the intensity being in the low binding energy peak. We propose to describe the observed 3d structure by the screening of the 3d hole by means of a charge transfer from the new hydrogen band to the empty 4f level, the latter being pulled down below the hydrogen band. This would be a shake down process as in La metal.

The presence of temperature dependent superstructure lines in the neutron diffraction pattern of LaD 3 suggests the occurence of a low temperature phase transformation. It is of second order and probably due to an ordering of the D atoms on off-centre positions in the octahedral interstices of the metal atom network. The structural analogy with fluorite type superionic conductors is emphasized.

This paper reviews some recent results on the interaction of gaseous hydrogen with solid substrates of metals to form hydrides. A first part refers to theoretical and experimental aspects of the chemical process at the metal surface; the surface can be crystalline, ordered or desordered, clean or precovered with C, S, CO or oxidised. The second part is concerned with the main steps of the chemical reaction which are the nucleation and growth of the hydride phases.

Absorption and desorption isotherms of FeTiDx (0≤x≤1.9) were measured at room temperature. They indicate isotope effects. The dependence of the crystal structure of FeTiDx on D2-pressure (≤153 bar) was investigated at room temperature by means of neutron diffraction on powder samples both in absorption and desorption. The results show that the distribution of the deuterium atoms in the orthorhombic β-phase change from 0.880.12 for the DI/DII sites at x=1.0 (1) to 0.920.45 at x=1.4. This can be interpreted as a transition from a β1-phase of composition FeTiD to a β2-phase of approximate composition (FeTi)3D4. For the last composition Lebsanft (2) has reported a 0.700.70 distribution over the two D-sites. In agreement with (3) the structure of γ-FeTiD (x>1.9) is found to be monoclinic (space group P2m). Associated with considerable lattice expansions deuterium atoms occupy both in β- and γ-phases octahedral sites.

2014 Surface segregation with the disproportionation into La and Th oxide plus precipitations of elemental Ni play an important role in the understanding of the easy hydrogen absorption of LaNi5 and of the catalytic properties of ThNi5. By means of core-level X-ray photoelectron spectroscopy we show that the chemisorption of O2, H2O, and H2 on LaNi5 surfaces induces a strong, weak and no surface segregation, resp. Precoverage with SO2 blocks further segregation, whereas exposure to H2S does not. The oxygen induced segregation of ThNi5 at room temperature is much weaker than in LaNi5, but is very extensive at 200 °C. J. Physique 42 (1981) 1025-1028 JUILLET 1981

The crystal and magnetic structures of polycrystalline CeDx(2.2 or=2.90 remains approximately cubic down to 1.5K, second-order phase transitions to ordered structures with tetragonal symmetry (basic translations at approximately ac, ct approximately 2ac, space group I4; in contrast to Titcomb and co-workers (1974)) occur at temperatures Tc=290(3) and 330(5)K for x=2.18 and 2.29 respectively. Between x=2.29 and x=2.96 the magnetic ordering changes from ferromagnetism (Tc=3.7(2)K, ordered magnetic moment mu (Ce3+)=1.1(1) mu B at 1.3K) to FCC II antiferromagnetism (TN=4.2(2)K, mu (Ce3+)=0.6(1) mu B at 1.3K, mu //(111)).

Photoemission studies combined with measurements of the magnetic susceptibility show that La segregates to the surface of La${\mathrm{Ni}}_{5}$ in the presence of ${\mathrm{O}}_{2}$ or ${\mathrm{H}}_{2}$O, and the Ni precipitations are formed during hydrogenation. This represents a self-restoring mechanism of the active surface, since the highly reactive La removes the oxygen and keeps the Ni metallic. Dissociative adsorption of ${\mathrm{H}}_{2}$ may then occur at the Ni atoms.

Photoemission (XPS and UPS) and inverse photoemission spectra (BIS) of CoS have been measured. From these data the occupied and empty density of states of this material are deduced. The metallic nature of CoS is not caused by a breakdown of Mott-insulation but rather because of Co(d) - S(p) hybridization.

We explain the irreversible change of the magnetic properties of FeTi upon hydrogenation, the activation process and some surface properties of FeTi by surface segregation. In a surface layer Ti diffuses to the surface and Fe forms magnetic precipitations which probably catalyze the hydrogenation. The catalytically active surface is renewed with each cycle of hydrogenation.

The formation of MgH2 directly from magnesium and molecular hydrogen is extremely slow; however, reasonable hydrogenation kinetics have been reported in compounds and alloys of magnesium with nickel, copper and rare earth metals. Using X-ray photoemission spectroscopy and Auger electron spectros-copy, we analysed the chemical states and the concentrations of magnesium, nickel and copper at the surface of the eutectic alloy MgMg2Ni and of the intermetallic compounds Mg2Ni and Mg2Cu. Air-exposed samples are greatly magnesium enriched on their surface, the magnesium being oxidized. Surfaces cleaned in ultrahigh vacuum show segregation of magnesium under the influence of oxygen even at room temperature. The segregated magnesium oxidizes and keeps the nickel and copper in the metallic state. Molecular hydrogen can be dissociated at the metallic nickel or copper particles or at the metallic subsurface. The catalytic activity of Mg2Ni and Mg2Cu in the hydrogenation of magnesium observed by Reilly and Wiswall is therefore due to a surface decomposition which continues the supply of atomic hydrogen.

The μ+ Knight shift in Platinum has been measured between 20 K and 785 K. It shows a strong temperature dependence and scales with the magnetic bulk susceptibility. A temperature independent contribution of +53±15 ppm and a d-electron induced hyperfine field per unpaired d-electron per atom of BhfdΩa=−5.03 kG(±8.5%) are obtained. The μ+ Knight shift in PdH0.70, PdH0.75 and PdH0.86 shows no dependence on temperature between 20 K and RT and increases from Kμ=−(8±3) ppm for x=0.70 to K =+(6.5±3) ppm Kμ=+(6.5±3) ppm for x=0.86, in good agreement with proton Knight shift measurements.

Surface core level shifts Δ c s of Au, Pd, Rh, Sc, and Ca have been measured by photoemission.

We have analysed the low-temperature electronic properties of CeH x of compositions close to the metal-semiconductor transition by measuring the specific heat (1.5 to 15 K) and photoelectron spectra (25 to 300 K) at different energies ( h ω = 25 to 55 eV and 115 to 122 eV ) using synchrotron radiation. Two important findings result from our investigations. Firstly, above 5 K the coefficient γ of the electronic specific heat of CeH 2.65 is fairly large (110 mJ mol −1 K −2 ) as compared with that of the corresponding lanthanum hydride (not greater than 0.04 mJ mol −1 K −2 ) suggesting heavy-electron type behaviour. An unambiguous demonstration of heavy-electron behaviour is impeded by the occurrence of magnetic order below 4 K. Secondly, a strong peak of about 1 eV FWHM appears at E F below 70 K in the photoelectron spectra. From the energy dependence and from the presence of a similar peak in LaH 2.7 we conclude that the peak is not caused by f electrons. Evidence for a surface semiconductor-metal transition due to the formation of cerium dihydride at low temperature at the surface is given.

By means of XPS and AES we have analysed the chemical states and the concentrations of Mg and Ni at the surface of the hydrogen storage materials MgMg2Ni eutectic alloy and Mg2Ni intermetallic compound. Mg2Ni decomposes at the surface into Mg oxide and metallic Ni. Molecular hydrogen can be dissociated at the metallic Ni precipitations or at the metallic subsurface layer. Thus the proposed model describes the catalytic effect of Mg2Ni on the hydrogenation [1] of Mg by surface decomposition and the ability to supply atomic hydrogen. With a similar model we described already successfully catalytic effects at the surface of LaNi5 and FeTi [2]. It is likely that it is applicable to other Mg compounds, too.

Activation of pure stoichiometric FeTi turned out to be difficult and deactivation processes due to gas impurities limit the hydrogen storage capability. Isotherms of deuterium desorption are reported for the temperature range T = (25÷70)°C. At room temperature the crystal structures of FeTiD x (x = 0÷1.74) and FeTiH 0.78 D 0.22 were investigated by means of neutron diffraction at D 2 -pressures up to 84 bar. Deuterium absorption in FeTi yields ternary deuterides and is associated with symmetry reduction corresponding to considerable distortions of the CsCl-type metal structure. In FeTiD deuterium occupies octahedral sites with two iron and four titanium atoms as nearest neighbour coordination (space group P222 1 or P 2 c ). Hydrogenation does not change essentially the order parameter of FeTi.

Measured and computed 3d core level photoemission spectra for Yb in YbP are presented. The theoretical line shapes and satellite structures are obtained from a combination of standard atomic calculations in intermediate coupling, and many-body techniques due to Gunnarsson and Schoenhammer.

The crystal structure of the hydrogen storage system γ-TiFeD 1.94(3) was re-investigated by neutron powder diffraction profile analysis at room temperature and 113 ± 17 bar D 2 pressure. In contrast with previous work which assumed a structure of monoclinic symmetry a structure of orthorhombic symmetry was assumed: space group Cmmm ; lattice parameters a = 7.029(4) A , b = 6.233(2) A , c = 2.835(1) A ; titanium in equipoint 4h ( x , 0, 1 2 ), x = 0.223(2); iron in 4i (0, y , 0), y = 0.2887(7); D1 in 4e ( 1 4 , 1 4 , 0); D2 in 2c ( 1 2 , 0, 1 2 ); D3 in 2a (0, 0, 0); agreement values after profile refinement R wp = 0.160, R I = 0.085, R F = 0.060; ( sin θ λ ) max = 0.59 A − 1 ; 85 inequivalent contributing reflections hkl ; 10 refined structural parameters. Refinements based on the less symmetric monoclinic model yield virtually the same fit and structure but require four more structural parameters. The structure is characterized by three types of octahedral metal atom interstices; two of type Ti 4 Fe 2 occupied by deuterium atoms D1 and D3 and one of type Ti 2 Fe 4 occupied by deuterium atom D2. The former are 100% occupied and the latter are 91% occupied. The shortest interatomic distances are Fe − D1 = 1.77 A , Ti − D2 = 1.95 A and D1 − D3 = 2.35 A .

Positive muon μ+ spin rotation measurements have been performed in a single-crystal PdH0.74 sample between 20 and 150 K. The μ+ depolarization rate σ has been measured as a function of crystal orientation on a magnetic field. With increasing temperature a strong reduction in the σ anisotropy occurs, whereas only a moderate decrease in average depolarization rate is observed. It is assumed that protons and muon occupy octahedral interstitial sites in the palladium lattice. The data can be fitted by a decreasing proton occupancy of the octahedral sites nearest the μ+ with increase in temperature. The proton occupancy of the remaining octahedral sites at all temperatures, as well as the occupancy of the proton sites nearest the μ+ at 20 K, is compatible with the bulk nominal hydrogen concentration x = 0.74. It appears that at 20 K the μ+ would stay at a location with “regular” nearest-neighbour proton occupancy, but that at higher temperatures diffusion or reordering would allow the μ+ to find an environment with less nearest-neighbour protons.

Surface studies by means of AES and XPS show that during the activation process of FeTi surface segregation occurs. In a surface layer Ti diffuses to the surface and metallic Fe clusters are formed. They catalyze the hydrogen absorption and are the reason for the irreversible change of the magnetic properties of FeTi upon hydrogenation. At room temperature the surface segregation is not effective enough to restore the catalytic active surface so that FeTi is deactivated easily in air.

Though there is continuing interest in basic research on hydrogen in, and on, metals, applied research on metal hydrides has known many ups and downs. About ten years ago it was thought that hydrides of intermetallic compounds would become important in the mobile and stationary storage of hydrogen as a synthetic fuel. Subsequently it became evident that hydrogen would not be an economic fuel in the immediate future, unless the cost of removing pollution was added to the price of fuels. Today applied research on metal hydrides is more oriented towards the use of hydrogen in closed systems, e.g. , thermal compressors or heat pumps [1]. The aim of the present contribution is to show that metal hydrides are exciting materials allowing the study of many topics of solid state science.

Surface studies by means of AES and XPS show that during the activation process of FeTi titanium diffuses to the surface and metallic iron clusters are formed. They catalyze the hydrogen absorption and are the reason for the irreversible change of the magnetic properties of FeTi upon hydrogenation. At room temperature the surface segregation is not effective enough to restore the catalytic active surface so that FeTi is deactivated easily in air. Structural studies of FeTi, FeTiD and FeTiD1.74 were performed. The best agreement between observed and calculated intensities of FeTiD is obtained with space groups P2221 (Pmc21) and P2/c. The lattice parameters of the orthorhombic unit cell are a = 2.966 A , b = 4.522 A and c = 4.370 A .

The VB and the core levels of clean and oxygen exposed bulk samples of La and LaNi5 were investigated by means of photoelectron spectroscopy using MgKα (XPS) and HeII (UPS) radiation. The HeII VB of La only shows 1.3 eV FWHM. The VB of LaNi5 is mainly derived from the VB of Ni. The low binding energy satellite of the La3d core level (4f1 final state) is much stronger in LaNi5 than in La, reflecting the better screening of the 3d core-hole by filling of f states. The spectra indicate clearly that La oxidizes and not Ni upon the exposure of LaNi5 to small amounts of oxygen.

The intermetallic compounds LaNi5, FeTi and Mg2Ni are Pauli paramagnets and therefore should not show any ferromagnetic resonance (FMR). Nevertheless FMR signals are observed in crushed samples and their intensity increases with the number of hydrogenation-dehydrogenation cycles. The FMR signal shows strong temperature dependence and for the pure Ni compounds it disappears just below the Curie temperature of pure Ni metal. The results are interpreted on the assumption that the FMR originates from superparamagnetic clusters that are formed by precipitating Ni or Fe atoms near the surface. The results are discussed in relation to previous magnetisation and surface measurements. Time-dependent behaviour observed at room temperature supports the superparamagnetic cluster picture, and is used to estimate the distribution of clusters on the surface. An additional narrower line with g=2.01+or-0.02 was observed at elevated temperatures and is attributed to magnetic resonance in the paramagnetic state.

Quantitative phase analysis by neutron powder diffractometry yields conclusive evidence for the irreversible decomposition of La7Ni3 into LaD3 and LaNi5 during deuteration at room temperature. Refinement of the LaD3 structure confirms that the D atoms are distributed over the tetrahedral and octahedral interstices of the f.c.c. metal atom arrangement. The D atoms occupying the octahedral interstices are not exactly at the centre but appear to be shifted away from it along different directions. It is suggested that this delocalization results from large anharmonic thermal displacements of the D atoms mainly along 〈111〉 directions. The crystal structure of La7Ni3 was refined both by single-crystal X-ray analysis and by neutron powder diffractometry. The results are compared and discussed in relation to other Th7Fe3-type structures.

FeTi is an interesting hydrogen storage material which has to be activated at ≈670 K for the absorption of hydrogen. We review critically the great number of previously published results and models on this activation process and emphasize the controversial points. To eliminate the controversy we analysed the variation of the surface composition of FeTi upon activation in the high-pressure cell of a photoelectron spectrometer. The initially passivating surface oxide is shown to be converted into a mixture of TiO2 and Fe by surface segregation and chemical reduction. No evidence for the formation of Fe2Ti4O x , FeTiO x , and TiH x is found. H2/D2 exchange reactions show that H2 dissociates rapidly on Fe and FeTi, but not on TiO2. The surface of FeTi is activated easily at 670 K. Difficulties encountered with the initial hydrogen absorption by virgin high purity FeTi are probably related to bulk (H diffusion, fracture toughness) rather than surface properties.

We have measured the Hall coefficient, the electrical resistivity and the magnetic susceptibility of liquid transition and rare-earth metals, and of their liquid alloys with normal metals. The interesting results are: A filling-up of the unfilled d-bands of liquid Fe, Co and Ni on alloying, positive Hall coefficients of the liquid rare-earth metals and a change of sign of these Hall coefficients on alloying.