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SmB62 single crystals were successfully grown by the floating zone (FZ) method. The high-temperature thermoelectric properties were investigated, together with magnetic properties and specific heat at low-temperature. The electrical resistivity, ρ, shows variable-range-hopping (VRH) behavior with significantly lower values than other rare-earth RB62 (RB66) compounds. An effective magnetic moment, μeff, of 0.42 μB/Sm was estimated, which if straightforwardly taken indicates a mixed valency for SmB62 with Sm2+:Sm3+ = 1:1, which is the first ever indicated for RB66-type compounds. Localization length of the VRH at the Fermi level, ξ, was estimated to be 3.33 A indicating that carriers in SmB62 are much less localized than in YB66 which has 0.56 A. The thermoelectric behavior of SmB62 is striking, with ρ reduced by two orders of magnitude while maintaining large Seebeck coefficients, and as a result the power factor is ∼30 times higher than other rare-earth phases. Overall the figure of merit ZT amounts to ∼0.13 at 1050 K, with an extrapolated value of ∼0.4 at 1500 K, an expected working temperature for topping cycles in thermal power plants; that gives a ∼40 times enhancement for Sm. Since there are few thermoelectric materials applicable for very-high temperature applications, this discovery gives new interest in the samarium higher borides.

The field emission properties of chemical vapor deposition (CVD) diamond thin films are investigated by measuring the field emission I–V characteristics, the emission site density and the field emitted electron energy distribution. The results are discussed with regard to field emission due to negative electron affinity (NEA) and classical Fowler–Nordheim emission due to geometrical field enhancement. The requirements on the diamond films for NEA mediated field emission are discussed. These requirements are high resistivity, low defect density and few grain boundaries. We show that diamond films matching these requirements are actually bad field emitters. On the other hand we show that the films exhibiting good field emission properties are just opposed to the above mentioned requirements; they exhibit low resistivity, high defect density and many grain boundaries as they are of nanocrystalline nature. The good emitting CVD diamond films are grown on p-type Si(1 0 0) using plasma enhanced CVD at substrate temperatures around 950°C and a gas mixture of 5% CH4 in H2. Using the example of multiwalled carbon nanotube emitter (MWNT) we show how the emitter work function and the local field at the emission site can be determined independently by measuring the field emitted electron energy distribution. For MWNT we find a work function of 4.9 eV and a local field of 2500 V μm−1 (for an emission current of the order of 10 pA). In the case of nanocrystalline CVD diamond emitter we find work function values around 6 eV and local electric fields again of the order of 2500 V μm−1. The electronic structure of the nanocrystalline CVD diamond field emitters is investigated using standard photoemission spectroscopy and simultaneous photoemission and field emission spectroscopy. From the presented measurements we can clearly relate the low field electron emission of the investigated nanocrystalline diamond films to classical Fowler–Nordheim tunneling due to local geometrical field enhancement.

Metal hydrides are used for electrochemical or gaseous storage of hydrogen because considerable amounts of hydrogen are reversibly absorbed and desorbed at interstitial sites. Palladium is often used as a model system. Nanophase material is of interest because properties related to the hydrogen absorption are size dependent. In this study, clusters from the size of 55 to 1415 atoms are investigated and compared with bulk Pd. It turns out that not only the amount of hydrogen per palladium that can be intercalated changes but also kinetics and chemical potentials are dependent on the cluster size. The clusters used for this study were chemically synthesised and stabilised by a ligand shell.

The crystallization behaviour of a glass in the SiO2-CaO-F system was analyzed using differential scanning calorimetry (DSC), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Three crystalline phases were detected according to ICDD patterns. The first phase formed at 583°C was identified as CaF2. The morphology was spherulitic with a diameter of approximately 100 nm. The second phase was formed at 664°C. It was identified as calcium fluoride silicate ‘Ca2SiO2F2’ (ICDD 35-0002). SEM investigation showed that the crystals were spherulitic with a diameter smaller than 100 nm. The crystals were precipitated in the volume of the glass and homogeneously distributed. As a third phase, cristobalite crystallized at 895°C. The simultaneous release of calcium and fluorine ions from the vitreous glass in lactate buffer solution at pH 4.0, simulating an acidic oral environment, was investigated using X-ray photoelectron spectroscopy (XPS). The release of calcium and fluorine ions is of special interest for dental applications. The atomic ratios of the components Si, Ca and F at the glass surface after different leaching periods were determined. In order to investigate the leaching process, concentration profiles were measured using ion beam sputtering with Ar+ -ions. The dependence of the atomic ratios of Si, Ca and F on the sputter time was determined in order to measure the depth of the leaching layers. Most probably, the release of calcium and fluoride was controlled by a surface layer rich in calcium and flourine ions which dissolved with increasing leaching time. After 2 min leaching, a fluoride-rich surface layer measuring approximately 10 nm was detected. The atomic ratios of Si, Ca and F were different from the bulk composition ratios in a surface reaction layer of 800 nm thickness. After 30 min leaching time, a calcium- and fluoride-rich surface layer approximately 50 nm thick was formed. The bulk composition was reached at a depth of approximately 500 nm. The main component in the surface layer, after 12 days leaching in acidic environment, was silicon.

Hydrogen is hailed as a non-polluting synthetic fuel that could replace oil, especially for transport applications. The technology to make this a reality — particularly hydrogen-storage materials — has been a long time coming, but the first commercial vehicles might now be only a few years away.

Complex metal oxides, such as e.g. perovskite-type phases are developed as potential functional materials to improve the efficiency of thermoelectric converters. Among those, cobaltates with p-type conductivity and n-type manganates are considered for the realisation of a ceramic thermoelectric converter. Sintered pellets with the composition AMO3–δ (A = Ln, RE; M = Co, Mn, Ni, Ti) and “Ca3Co4O9 derivates” were synthesized and characterised concerning their thermoelectric properties in a broad temperature range. It was found that the Seebeck coefficient and the electrical conductivity do not depend on the dimensions of the crystallites, while the heat conductivity can be substantially lowered by decreasing the size of the crystalline domains in these systems. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron field emission has been performed from a 5 μm indium cluster sitting on a nitrogen doped diamond (100) surface (3×3×1 mm3). The motivation to study such a system arose from the fact that electron field emission from N-doped diamond was reported in literature. However, the emission mechanism is not really known and still the subject of an intense discussion in the diamond/amorphous carbon community. We have chosen this setup to conduct a model experiment with well-defined parameters. The emission properties were analyzed by energy resolved field emission (FEED). We found that electron emission takes place at the apex of the indium grain for a hydrogenated diamond surface. However, large energy shifts were observed in the FEED spectra due to a potential drop across the hydrogen saturated surface. An oxygen termination kills the emission. By sputtering the surface the emission reappears with much lower energy shifts in the FEED spectra due to the conductive sp2 layer. We present a model taking into ...

We investigated natural p-doped (100) diamond by means of STM. To achieve a smooth and clean surface, the diamond was polished in a hydrogen plasma at 870°C. In contrast to previous work, the STM measurement have been done on an etched and not on an overgrown diamond surface. After the hydrogen treatment the surface was free of any contamination, and we characterised the smoothing process with AFM and LEED. While the roughness of the surface was determined by AFM to be lower than 0.8 nm (RMS) LEED showed a (2 × 1) reconstruction without any annealing. UPS measurements revealed the surface to have a negative electron affinity (NEA). STM at ambient conditions showed dimer rows of the (2 × 1) monohydride reconstructed surface. Large atomically flat terraces (> 17 nm × 17 nm) were found on the hydrogen-plasma treated surface, which is an indication of effective surface polishing.

Note: Times Cited: 81-2Third International Symposium on Metal-Hydrogen Systems, Fundamentals and Applications8-12 June 1992Jun 08-12, 1992Uppsala, Sweden Reference EPFL-ARTICLE-206084 URL: ://WOS:A1994NQ70600044 URL: ://INSPEC:4763663 Record created on 2015-03-03, modified on 2017-05-12

Note: Times Cited: 101-2International Symposium on Metal-Hydrogen Systems: Fundamentals and ApplicationsJun 08-12, 1992Uppsala, sweden Reference EPFL-ARTICLE-206008doi:10.1524/zpch.1994.183.Part_1_2.371View record in Web of Science Record created on 2015-03-03, modified on 2017-07-07

For many applications AB 5 type hydrogen storage alloys are still too expensive. We report on the results of studies aimed at lowering the alloy costs by partial substitutions of A and B elements respectively. We have improved the capacity of silicon-containing cobalt-free AB 5 -type alloys by optimization of the La:Ce ratio in the A component and by the substitution of aluminium by manganese in the B component. The alloy Lm 0.5 Mm 0.5 Ni 4.2 Mn 0.2 Al 0.3 Si 0.3 (Mm, rare earth mischmetal; Lm, lanthanum-rich mischmetal) showed a maximum capacity of 270 mA h g −1 and good cycling stability, i.e. the optimum in price/performance ratio. Substitution of larger amounts of nickel with copper could further lower the price of such alloys; however, these copper-containing alloys showed low kinetics and a slow activation. Electrochemical measurements were carried out on ten different single-phase AB 5 alloys and on a two-phase AB 5.36 -type alloy. Up to 500 charge-discharge cycles were performed. Samples were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis and photoelectron spectroscopy. Photoelectron spectroscopic analysis of Lm 0.5 Mm 0.5 Ni 2.4 Cu 2 Mn 0.25 Si 0.35 after 30 electrochemical charge-discharge cycles points to a thick nickel oxide top surface layer, no enrichment of metallic nickel in near surface layers and to a slightly enhanced metallic copper subsurface layer. No passivating silicon surface oxide film could be found. We attribute the low electrochemical kinetics of this alloy to the absence of metallic nickel at the electrode-electrolyte interface.

The surface analysis of Zr–V–Fe getter alloys by means of x‐ray photoelectron spectroscopy shows that the H2O and CO dissociation to form metal oxides and carbides is less important than the O2 dissociation at 300 K. These results are well correlated with theoretical and experimental dissociation energies for the molecules on metal surfaces. A thin passivated layer formed on the metal surface after 1 L CO exposure prevents further CO molecules from dissociating, but O2 dissociation continues. Heating the Zr–V–Fe getter up to 700 K yields an increase of H2O and CO dissociation. The metal surface is less oxidized after O2 exposure at 700 K than at 300 K because oxygen atoms diffuse from the surface into the bulk.

A nonequilibrium Mg hydride was prepared by low temperature hydrogen implantation in Mg thin films. In contrast to the usual compound in which H is charged under high pressure and elevated temperature, no structural phase transformation from hexagonal to tetragonal is observed here. Implanted H atoms progressively fill the tetrahedral interstitial sites of the Mg hexagonal cell up to a concentration H/Mg around one. The resulting hydride is metallic whereas the classical MgH2 is an insulator.

We have evaporated atomic monolayers of magnesium on polycrystalline PdHx and observed, by means of photoelectron spectroscopy, interdiffusion of hydrogen and the formation of an MgH2 overlayer at low temperatures. Above 170 °C hydrogen desorbs rapidly. After hydrogen desorption, interdiffusion occurs at the Mg-Pd interface. We also prepared magnesium-rich Mg-Li alloys and studied the absorption of hydrogen, in order to investigate possible metallization. Reactivity around room temperature is very slow; at 300–400 °C the Mg-Li alloy decomposes and MgH2 is formed.

57Fe Mossbauer, X-ray photoemission and Ce LIII edge X-ray absorption measurements on CeFe2, selected pseudobinaries Ce(Fe1 − yXy)2 and some of their hydrides were carried out to shed light on magnetic ordering in these materials. While the hydrides order ferromagnetically in the temperature range below Tc, a double transition is observed in the pseudobinaries. At Tc, ferromagnetic ordering sets in, followed by an antiferromagnetic phase below a lower-lying critical temperature Tc2, their magnetic ordering type having been found to be of some complexity. In the parent compounds, cerium is of a non-integral valency, i.e. it contains 4f0 admixture. On hydrogen absorption it changes to 3+, corresponding to 4f1.

We observe nonmetallic electronic states above the Fermi level in single-walled carbon nanotubes by measuring the energy distribution of thermal-field-emitted electrons. This measurement method examines electronic states associated with the nanotube cap or end termination, and with it, we resolve electronic states greater than 3 eV above the Fermi level. The observed emitting states are broad at high temperatures (0.7–1.5 eV full width at half maximum), and the peak positions shift linearly with applied voltage. We present possible mechanisms responsible for these states.

We present the atomically resolved room temperature scanning-tunneling microscopy study of bias dependent images of charge density waves (CDWs) in $1T\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{Se}}_{2}$. With the help of angle-resolved photoemission of the CDW-split $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}{d}_{{z}^{2}}$ band in $1T\text{\ensuremath{-}}\mathrm{Ta}{\mathrm{Se}}_{2}$, we determine the electronic location of $\mathrm{Ta}\phantom{\rule{0.2em}{0ex}}{d}_{{z}^{2}}$ subbands on inequivalent atoms of the reconstructed Ta plane. We thus demonstrate the atomic origin of the CDW-formation related effects observed in the band structure of this material.

The case of a 20 month-old girl that was admitted to the emergency ward because of worsening of her general condition in the setting of acute non-bloody gastroenteritis is reported. The clinical examination revealed signs of severe dehydration and a prominent tender abdomen. Laboratory evaluation showed leucocytosis, elevated C-reactive protein and severe hypochromic microcytic anemia. Abdominal X-ray revealed diffuse meteorism. The child underwent laparascopic evaluation. A perforated Meckel's diverticulum was found. Perforation and anemia due to occult bleeding are unusual presentations of Meckel's diverticulum. The differential diagnosis of children presenting with an acute abdomen with special focus on Meckel's diverticulum is discussed.

Titanium is a commonly used biomaterial for dental and orthopaedic applications. To increase its ability to bond with bone, some attempts were made to coat its surface with calcium phosphate (CaP). This paper describes a new type of coating. Instead of a pure CaP layer, a mixing of titanium dioxide (TIO2) and CaP is fabricated and deposited as a coating. These layers are deposited by a sol-gel route on pure titanium substrates using various pre-treatments. The method consists of mixing a solution of tetrabutyl ortho-titanate or a sol of titanium dioxide with a solution of calcium nitrate and phosphorous esters. This composite is deposited on to commercially pure titanium plates, mechanically polished or blasted with pure crystalline aluminum oxide, using the spin-coating technique. These coatings are then fired at 650 or 850 degrees C for various times. The samples are characterized by X-ray diffraction for their crystallinity, X-ray photoelectron spectroscopy for their surface chemical composition and scanning electron microscopy for their topography. Samples treated at 850 degrees C present a well-pronounced crystallinity, and a high chemical purity at the surface. The topography is strongly related to the viscosity of the precursor and the substrate pre-treatment. Possibilities to structure the outermost layer are presented.

Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We report on angle-resolved photoemission experiments of the Y trihydride phase. Most importantly, we find the absence of metal d bands at the Fermi level and a set of flat, H-induced bands located at much higher binding energy than predicted, indicating an increased electron affinity at H sites.

Nanostructured graphite was prepared by mechanical milling under a hydrogen atmosphere. Several samples obtained after different milling times were systematically examined to get fundamental information about the structures, hydrogen concentrations, and also hydrogen desorption properties. The hydrogen concentration reaches up to 7.4 mass% (CH 0.95 ) after milling for 80 h, and two desorption peaks of hydrogen molecule (mass-number=2), starting at about 600 K and 950 K respectively, are observed inthermaldesorption mass-spectroscopy in the sample. Below the temperature of the second desorption peak, at which recrystallization related desorption occurs, the nanostructured graphite is expected to retain its specific defective structures mainly with carbon dangling bonds as suitable trapping sites for hydrogen storage.

Investigation of the current-time (I-t) characteristics of field emission (FE) from single-walled carbon nanotubes (SWNT), does not show any significant dependence on ambient partial pressures to 10e-5 mbar of hydrogen or water. It is however shown that oxygen causes substantial reduction of the FE current and this is believed to be related to reactive etching/oxidation of the nanotubes. By heating the tubes up to 1100 Kelvin an increased instability in the FE current as well as on the field emission microscopy (FEM) screen can be observed. These instabilities become less and less pronounced after repeated annealing steps. FEM during short-time heating reveals dim five-fold as well as six-fold feinstructures. These feinstructure FEM patterns are not stable and have a short lifetime. Resonant tunnelling states as well as FE from nanotube cap states might explain these observations.

XPS spectra for HfNx films made by bias magnetron sputtering are reported over the range x from 0.64 to 1.11. They indicate that the valence band comprises a shoulder immediately below the Fermi level EF and a peak at some 6 eV below it for all compositions x, due to the Hf 5d and 2p bands respectively. At compositions of HfN0.80 and above, the following effects were found in the core levels as x was increased: the intensity of the Hf 4f 5 2 appeared to increase, relative to the Hf 4f 7 2 , due to the development of the N 2s below it. The binding energy of all hafnium levels increases whereas the N 1s remains invariant. The decrease in the relative binding energy is presumed to be due to increasing ionicity of the bonding. The data also appear to indicate that the additional lattice defects present in the films over and above those resulting from the substoichiometry do not affect the spectra. Below HfN0.75 the core level data indicate a marked increase in ionicity which could be associated with a change in the behavior of the lattice parameters. This change is thought to be caused by the ordering of vacancies on the nitrogen sublattice.

The Pauli paramagnetic Th7Fe3 was reported to form the ferromagnetic hydride Th7Fe3H30 with the Curie temperature Tc ≈ 350 K. We show that Th7Fe3 if hydrogenated violently disproportionates into Th4H15 and into a Fe-rich ferromagnetic Th-Fe-compound. When hydrogenated slowly, a ternary hydride Th7Fe3H≈24 of unknown structure is formed. The ternary hydride is not ferromagnetic down to 80 K. XPS analysis reveals that the 2p3/2 electron states of Fe are chemically shifted from 707.0 eV binding energy in elemental Fe to 706.6 eV in Th7Fe3 indicating an electronic charge transfer to the Fe. Oxygen exposure causes surface segregation with the formation of Th oxide and Fe precipitations which accounts for the readiness of hydrogen absorption by Th7Fe3.

The analysis of the valence band photoemission spectra of Ce compounds is inspected. It is found that the data and the models agree in that they give a 4f hole state at a binding energy of ∼2 eV and a 4f band near (within ∼100 meV) the Fermi energy. The implications of photoemission data for the electronic structures of heavy fermion systems is discussed.

The surface properties of ZrMn 2 and TiMn 2−x ( x = 0, 0.5) were investigated using X-ray photoelectron spectroscopy because of the readiness of hydrogen sorption of many AB 2 compounds. The concentration of the components and their chemical state were analysed in samples which had been fractured in an ultrahigh vacuum, exposed to increasing doses of oxygen and air and subjected to hydrogen absorption and desorption. It is concluded that surface segregation accounts for the ease with which hydrogen is absorbed. Manganese, but not zirconium or titanium, segregates and is preferentially oxidized. Zirconium and titanium are assumed to form metallic precipitates on the subsurface below the oxidized manganese. The precipitates and the subsurface can catalyse the H 2  2H reaction. Furthermore the precipitates themselves may form hydrides and spill over atomic hydrogen to the intermetallic.

The magnetic properties of amorphous iron rich Fe-Zr alloys and their variations with hydrogenation have been studied by 57Fe Mossbauer spectroscopy and magnetization measurements. Hydrogenation increases both the Curie temperature and the magnetic moment per iron atom. Conversion Electron Mossbauer Spectroscopy (CEMS) showed drastic differences in the compositions of the surface and the bulk material of these alloys.

FeTi and the oxygen-stabilized compound Fe 2 Ti 4 O x are known to form reversible metal hydrides. However, whereas samples of Fe 2 Ti 4 O x which have been exposed to air readily react with gaseous hydrogen at room temperature, FeTi samples have to be activated. We analysed the surface properties of Fe 2 Ti 4 O x and of FeTi before and after activation by means of photoelectron spectroscopy. A high pressure cell inside the spectrometer allowed us to analyse the samples immediately after the high pressure high temperature activation, thus avoiding a transfer in air. Elemental iron(0) and titanium(IV) are formed on the activation of FeTi; we have no evidence for the formation of TiH x , Fe 2 Ti 4 O x or FeTiO x . Significant differences between the oxidation behaviour of Fe 2 Ti 4 O x and that of FeTi fractured in an ultrahigh vacuum were found at room temperature.

The hydrogen storage compound LaNi5 is an exchange-enhanced Pauli paramagnet with susceptibility chi (LaNi5)=4.6*10-6 EMU g-1. Hydrogen absorption leads to a decrease of the susceptibility of chi (LaNi5H6.0)=1.3*10-6 EMU g-1. This decrease is usually covered by a strong irreversible increase of surface magnetism, where, through surface segregation and decomposition, superparamagnetic Ni precipitations are formed. The two effects explain the controversial results about the magnetic properties of the LaNi5 hydride. The implication of this decomposition on the cyclic lifetime is discussed.

The growth of a strong peak at ${E}_{\mathrm{F}}$ is observed in photoelectron spectra of Ce${\mathrm{H}}_{2.7}$ below 70 K in addition to the hydrogen-induced band at 5 eV and the $4f$ emission at 2 eV. From the photonenergy dependence and from the absence of $4f\ensuremath{-}4d$ resonance enhancement we conclude that the peak is neither $4f$ derived nor related to screening or Kondo resonance, but is due to a surface semiconductor-metal transition. It can be explained by the removal of hydrogen from surface sites which pushes $d$ states from the hydrogen band back to ${E}_{\mathrm{F}}$ and results in a metallic surface dihydride.

The hydriding characteristics of La7Ni3, LaNi and Ce7Ni3 have been investigated. These compounds form the stable hydrides La7Ni3H19.3, LaNiH3.85 and Ce7Ni3H19.2. In structural and magnetic investigations La7Ni3is found to decompose into LaH3 and LaNi5 on rapid hydrogenation. On desorption at elevated temperatures the original La7Ni3 structure is reformed. An analogous decomposition is found in Ce7Ni3. The enthalpies of formation ΔH have been measured calorimetrically for the hydrides of LaNi compounds. ΔH varies linearly with the LaNi composition, independently of the various compound structures and of structural transformations on hydrogenation. The experimental values of ΔH are described by a phenomenological model. Despite their high hydrogen content, these hydrides are not suitable for use as hydrogen storage materials because of their high stability.

X-ray photoemission spectroscopy (XPS) has been used to study the surface reaction of Zn3P2 single crystals. The spectra of crystals exposed to H2, O2, CO2, O2+H2O or CO2+H2O during a four week period were compared to the spectra of as-grown or in UHV scraped samples. For samples contaminated with the wet gases O2+H2O and CO2+H2O additional phosphorus core levels together with a shift of the zinc core levels were observed. For crystals exposed to atmosphere during several months no phosphorus could be detected on the gasgrown surface, whereas the stochiometry of Zn3P2 was maintained within the bulk. Crystals with scraped surfaces showed no moisture sensitivity. No surface contamination was also detected for Zn3P2 crystals deposited with up to 1000 L H2O or exposed to atmosphere during 30 min.

We present UV-BIS spectra ( hv = 9.7 eV) of YH 1.9 , LaH 1.8 and CeH 2.1 . These compounds are metallic and they exhibit a non-vanishing density of states at E F . Two weak, d-derived structures around 1.0–1.5 eV and 2.5–3.0 eV above E F are observed as common features. In the LaH 1.8 spectrum a prominent peak is seen at 5.2 eV. Because the cross section for transitions into empty 4f states is very small at this low photon energy we believe that these are states with considerable 4f-valence band mixing. A relation to earlier core level results is briefly discussed.

We have analyzed the valence band region and the 3d core levels of Ce, CeH2.1 and CeH2.9 by means of X-ray photoelectron spectroscopy. Hydrogen induced states appear about 5 eV below EF. The density of states at EF is about 4 times smaller in CeH2.1 than in Ce and vanishes completely in CeH2.9 in agreement with the metal to semiconductor transition which was observed in resistivity measurements. The 4f level is well split off the hydrogen induced band at 2 eV for both hydrides. The 3d core levels are shifted by 1.9 and 2.1 eV from Ce to CeH2.1 and CeH2.9, resp., and exhibit intense satellites on the low BE side. A simple method to prepare large, compact samples of rare earth hydrides is described.

The authors point out that the measured Ce 3d core level spectra (XPS, XAS) of heavy-fermion compounds of Ce exhibit no high-binding-energy satellite (300K). The absence of this 4f0 satellite signifies according to the Gunnarsson-Schonhammer model (1983) that these compounds are gamma -like with n4f approximately=1 due to a 4f ground-state level not at EF, but below EF. Accordingly, the spectral 4f weight at EF is small.

Intermetallic compounds with d-transition metals have been used as catalysts. XPS and AES studies and the magnetic properties of LaNi 5 and FeTi show that surface segregation occurs and that superparamagnetic Ni and Fe precipitates are formed at the surface, catalyzing the dissociation of molecular hydrogen. The catalytic activity of many intermetallic compounds can be explained by surface segregation and the formation of d-transition metal precipitates. Contaminants often drive the segregation, hereby prolonging the lifetime of the catalyst. We predict that FeTi can replace Fe-catalysts being more resistant to contaminants.