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Electronic structure investigation of the cubic inverse perovskite Sc3AlN

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Abstract

The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to those of ScN and Sc metal, have been investigated by bulk-sensitive soft-x-ray emission spectroscopy. The measured Sc L, N K, Al L1, and Al L2,3 emission spectra are compared with calculated spectra using first-principles density-functional theory including dipole transition-matrix elements. The main Sc 3d–N 2p and Sc 3d–Al 3p chemical bond regions are identified at −4 and −1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L2,3 emission from Sc3AlN in comparison to that for pure Al metal is found, which reflects the Sc 3d–Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structures of Sc3AlN, ScN, and Sc metal are discussed in relation to the change in the conductivity and elastic properties.

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... At nonresonant 625 eV excitation energy, the L 3 /L 2 branching ratio increases from 1.9 for Cr 0.51 N 0.49 to 4.4 for Cr 0.44 Mo 0.09 V 0.08 N 0.39 . Quantitatively, the significantly higher L 3 /L 2 ratio for the Cr 0.44 Mo 0.09 V 0.08 N 0.39 sample compared with the statistical ratio (2:1) is due to the more effective Coster-Kronig process in conducting systems compared with more localized electrons with less conduction of the Cr 0.51 N 0.49 sample [74]. ...
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... sample. 68 The N 1s RIXS spectra representing the partial-DOS of N valence region follows the 2p → 1s dipole transitions. The N 1s RIXS spectra excited of all the samples at resonant photon energy of 397.3 eV exhibits a main peak centered around 389.9 eV composed of primarily N 2p states, in agreement with band structure calculations. ...
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Chromium-based nitrides are used in hard, resilient coatings, and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigated the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. Due to minuscule N vacancies, finite population of Cr 3d and N 2p states appear at the Fermi level and diminishes the band opening for Cr0.51N0.49. Incorporating holes by alloying V in N deficient CrN matrix results in enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared to Cr0.51N0.49. Further alloying Mo isoelectronic to Cr increases the density of states across the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. The hybridization effect with reduced N 2p states off from stoichiometry drives the system towards metal like electrical resistivity and reduction in Seebeck coefficient compensating the overall power factor still comparable to Cr0.51N0.49. The N deficiency also depicts a critical role in reduction of the charge transfer from metal to N site. The present work envisages ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.
... As observed in Fig. 3, the valence band edge shifts to higher energy with increasing x. The hybridization at the top of the valence band shows similarities with XES spectra of other nitrides e.g., Ti2AlN [35] and Sc3AlN [36]. ...
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... As observed in Fig. 3, the valence band edge shifts to higher energy with increasing x. The hybridization at the top of the valence band shows similarities with XES spectra of other nitrides e.g., Ti2AlN [35] and Sc3AlN [36]. ...
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... Later, Luo et al. [143] investigated the hypothetical Fe-containing 211 MAX-phases. However, more accurate calculations including all competing phases such as inverse perovskites [144] and quaternary phases showed that the Fe-containing 211 system was thermodynamically unstable [145]. Experimentally, a magnetic signal was later observed in Cr 2 − x Mn x GaC phases [146], and attributed to the presence of magnetic perovskite impurities. ...
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... The XAS and XES measurements were performed at room temperature (300 K) at the undulator beamline I511-3 at MAX II (MAX-IV Laboratory, Lund, Sweden), comprising a 49-pole undulator, and a modified SX-700 plane grating monochromator [21,22]. The measurements were made at a base pressure lower than 6.7*10 −7 Pa. ...
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This paper deals with the ground state of an interacting electron gas in an external potential v(r). It is proved that there exists a universal functional of the density, Fn(r), independent of v(r), such that the expression Ev(r)n(r)dr+Fn(r) has as its minimum value the correct ground-state energy associated with v(r). The functional Fn(r) is then discussed for two situations: (1) n(r)=n0+n(r), n/n01, and (2) n(r)= (r/r0) with arbitrary and r0. In both cases F can be expressed entirely in terms of the correlation energy and linear and higher order electronic polarizabilities of a uniform electron gas. This approach also sheds some light on generalized Thomas-Fermi methods and their limitations. Some new extensions of these methods are presented.
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The singularities of x-ray absorption or emission in metals are studied by a new "one-body" method, which describes the scattering of conduction electrons by the transient potential due to the deep hole. Using the linked-cluster theorem, the net transition rate in the time representation is expressed as the product of two factors: a one-electron transient Green's function L, and the deep-level Green's function G. These factors obey simple Dyson equations, which can be solved asymptotically by using Muskhelishvili's method. The x-ray transition rate is found to behave as 1εalpha, where ε is the frequency measured from the threshold, and alpha an exponent involving the various phase shifts deltal which describe scattering by the deep hole. alpha may be >0 (infinite threshold) or
Article
We present a nonempirical density functional generalized gradient approximation (GGA) that gives significant improvements for lattice constants, crystal structures, and metal surface energies over the most popular Perdew-Burke-Ernzerhof (PBE) GGA. The functional is based on a diffuse radial cutoff for the exchange hole in real space, and the analytic gradient expansion of the exchange energy for small gradients. There are no adjustable parameters, the constraining conditions of PBE are maintained, and the functional is easily implemented in existing codes.
Article
The anisotropy of the electronic structure of ternary nanolaminate V2GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeC are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: V 3d-C 2p bonding at −3.8 eV, Ge 4p-C 2p bonding at −6 eV, and Ge 4p-C 2s interaction mediated via the V 3d orbitals at −11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.
Article
The electronic structure of the heavy fermion compound CeB6 is probed by resonant inelastic soft-x-ray scattering using photon energies across the Ce 3d and 4d absorption edges. The hybridization between the localized 4f orbitals and the delocalized valence-band states is studied by identifying the different spectral contributions from inelastic Raman scattering and normal fluorescence. Pronounced energy-loss structures are observed below the elastic peak at both the 3d and 4d thresholds. The origin and character of the inelastic scattering structures are discussed in terms of charge-transfer excitations in connection to the dipole allowed transitions with 4f character. Calculations within the single-impurity Anderson model with full multiplet effects are found to yield consistent spectral functions to the experimental data.
Article
Thin films of the Mn+1AXn-phases Ti2AlC and Ti3AlC2 have been deposited by dc magnetron sputtering. In agreement with the Ti–Si–C system, the MAX-phase nucleation is strongly temperature dependent. At 900 °C epitaxial films of Ti2AlC and Ti3AlC2 were grown, but at 700 °C only a cubic (Ti,Al)C phase was formed. In addition, a perovskite carbide, Ti3AlC was grown at 800 °C. A bulk resistivity of 0.51 μΩ m, 0.44 μΩ m, and 1.4 μΩ m was measured for the Ti3AlC2, Ti2AlC, and Ti3AlC films deposited at 900 °C, respectively. By nanoindentation the hardness and Young’s module was determined for an epitaxial Ti3AlC2 film to 20 GPa and 260 GPa, respectively.
Article
The compounds (R3N)In (R=Sc, La–Nd, Sm, Gd–Tm, Lu) were synthesized by arc melting and sintering reactions from the binaries RN and R2In. Combined Rietveld refinements on X-ray and neutron powder diffraction data on the Ce-phase and X-ray diffraction for the other phases reveal the compounds (R3N)In to crystallize in the perovskite structure ((Ce3N)In: , a=504.89(2) pm; Rietveld: neutron powder diffraction: RF=0.056, RBragg=0.104, X-ray powder diffraction: RF=0.069, RBragg=0.115; refined composition Ce3InN0.92(1), chemical analysis Ce3InN0.91(2)O0.05(1)). Compounds R3In (AuCu3 structure type) are known for R=La–Sm. Nitrogen is able to stabilize this AuCu3-substructure with R=Gd–Tm, Lu and Sc. In measurements of the magnetic susceptibility (Ce, Pr, Nd, Sm, Tb: antiferromagnetic ordering at low temperature) and X-ray absorption spectroscopy at the R-LIII-edges the rare-earth atoms behave like R3+ species in insulating compounds. The electrical resistivity of the Sc, Ce and Nd compounds shows metallic temperature dependence. Chemical bonding was analyzed via LDA-COHP calculations for (La3N)In showing ionic polyhedra NLa6/2 embedded in a metallic matrix.
Article
For narrow band metals the distortions of the form of X-ray and X-ray photoelectron spectra are investigated under the influence of the vacancy on the inner level. A calculation method over the whole energy interval of the distoring influence of the hole field is proposed and realized numerically. The site formalism is developed to describe the X-ray spectra. Equations are obtained in the energetic representation which allow to effect a numerical analysis. Für Schmalbandmetalle werden die Verzerrungen der Form der Röntgen- und Röntgenphoto-elektronenspektren unter dem Einfluß einer Lücke auf das innere Niveau untersucht. Es wird eine Berechnungsmethode über das gesarute Energieintervall des Verzerrungseinflusses des ge-samten Feldes vorgeschlagen und numerisch realisiert. Der Platzformalismus zur Beschreibung der Röntgenspektren wird beschrieben. Gleichungen in der Energiedarstellung werden erhalten, die eine nuraerische Analyse ermöglichen.
Article
Sc3AlN with perovskite structure has been synthesized as the first ternary phase in the Sc–Al–N system. Magnetron sputter epitaxy at 650 °C was used to grow single-crystal, stoichiometric Sc3AlN(111) thin films onto MgO(111) substrates with ScN(111) seed layers as shown by elastic recoil detection analysis, X-ray diffraction, and transmission electron microscopy. The Sc3AlN phase has a lattice parameter of 4.40 Å, which is in good agreement with the theoretically predicted 4.42 Å. Comparisons of total formation energies show that Sc3AlN is thermodynamically stable with respect to all known binary compounds. Sc3AlN(111) films of 1.75 µm thickness exhibit a nanoindentation hardness of 14.2 GPa, an elastic modulus of 249 GPa, and a room-temperature electrical resistivity of 41.2 µΩ cm. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Article
ScN crystals were grown on tungsten foil by sublimation-recondensation method in the temperature range of 1840-2060degreesC, pressure range of 15-230 Torr under a nitrogen atmosphere. The growth rate increased exponentially with temperature with activation energy of 456.0 KJ/mol, and it was inversely proportional to pressure. The maximum growth rate was 79.292 mg/h at 2060degreesC under 25 Torr. Characterization methods confirmed the rock salt crystal structure with a lattice constant of 4.5005 Angstrom. (C) 2004 Kluwer Academic Publishers.
Article
A formalism to compute x-ray spectra due to core excitations in metals by using single-particle band-structure techniques is presented and illustrated with a detailed calculation of the $K,L$, and $M$ emission and absorption spectra of palladium over 200 eV. Within the muffin-tin approximation for the potential, any spectrum can be factorized into atomiclike and solid-state contributions. The atomiclike factor is the dipole transition strength connecting a core state to a muffin-tin orbital in a free-electron metal. The solid-state factor is proportional to the density of band states with angular momentum determined by the orbital symmetry of the core state and the dipole selection rules. These projected densities of states have been calculated by using a linearized version of the augmented-plane-wave method specifically designed to cover large energy ranges. In particular, the method can describe simultaneously several principal quantum numbers of the eigenstates (e.g., $4d$ and $5d$ for palladium).
Article
The mechanical properties of (001)‐, (011)‐, and (111)‐oriented MgO wafers and 1‐μm‐thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N 2 and Ar discharge, were investigated using nanoindentation. A combination of x‐ray‐diffraction (XRD) pole figures, high‐resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three‐sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as‐received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasing loads, increased in the order (011)≪(001)≪(111). After a 30 s postdeposition anneal at 1000 °C, however, hardness was found to be independent of load except at displacements ≫100 nm where substrate effects were apparent. TiN(001) and (111) films had hardnesses of 20±0.8 and 21±1 GPa, respectively, while data obtained from (011) layers exhibited large scatter due to surface roughness effects. Young’s moduli for annealed samples, calculated from the elastic unloading curves, were found to be 307±15 GPa for MgO (001) and 445±38 and 449±28 GPa for TiN (001) and TiN (111), respectively. © 1996 American Institute of Physics.
Article
Soft x‐ray emission spectroscopy is a common tool for the study of the electronic structure of molecules and solids. However, the interpretation of spectra is sometimes made difficult by overlaying lines due to satellite transitions or close‐lying core holes. Also, irrelevant inner core transitions may accidentally fall in the wavelength region under study. These problems, which often arise for spectra excited with electrons or broadband photon sources can be removed by using monochromatized synchrotron radiation. In addition, one achieves other advantages as well, such as the ability to study resonant behavior. Another important aspect is the softness of this excitation agent, which allows chemically fragile compounds to be investigated. In this work we demonstrate the feasibility of using monochromatized synchrotron radiation to excite soft x‐ray spectra. We also show new results which have been accomplished as a result of the selectivity of the excitation. The work has been carried out using the Flipper I wiggler beamline at HASYLAB in Hamburg using a new grazing incidence instrument designed specifically for this experiment. The photon flux at the Flipper I station (typically 5×10<sup>1</sup><sup>2</sup> photons per second on the sample with a 1% bandpass) is enough to allow soft x‐ray fluorescence spectra to be recorded at relatively high resolution and within reasonable accumulation times (typically, the spectra presented in this work were recorded in 30 min). The spectrometer is based on a new concept which allows the instrument to be quite small, still covering a large wavelength range (10–250 Å). The basic idea involves the use of several fixed mounted gratings and a large two‐dimensional detector. The grating arrangement provides simple mounting within a limited space and, in particular, large spectral range. The detector can be moved in a three‐axis coordinate system in order to cover the- different Rowland curves defined by the different gratings. The arrangement permits the use of gratings with different radii, which further facilitate the achievement of optimum performance over a large range. Two‐dimensional detection is used to allow a large solid angle, without suffering from loss of resolution due to imaging errors. The detector is based on five 2‐in. MCPs with resistive anode read out. The sensitivity of the detector, which is normally very low for soft x rays, especially at grazing angles, is enhanced by CsI coating and by using an entrance electrode.
Article
The new undulator beamline I511 at MAX-lab, now under commissioning, has been optimized for X-ray emission and photoelectron spectroscopies. Using an SX-700 high flux monochromator the accessible photon energy range is from 90 eV to about 1500 eV. The performance of the undulator agrees very well with the specifications, as shown by measurements using a photodiode. The energy resolution of the monochromator has been checked using absorption measurements in a gas cell. It was found to meet the expectations and exceeds a resolving power of 10 000 at 244 eV. The photon flux as a function of energy has been recorded as well and gives a maximum flux of 3×1013 photons/s/100 mA/0.1% BW. Beamlines I511 and I411 will be the first synchrotron beamlines making use of a so-called beam waist phenomenon, known from laser physics. We show results of ray-tracing calculations to determine the ultimate spot size on the sample location. The endstations to be used at this new beamline and their capabilities will be discussed as an example of the future use of this facility.
Article
A design of a small size grazing incidence instrument is presented, which offers large spectral range and high resolution without sacrificing luminosity. The instrument is particularly suited for use at synchrotron radiation sources since it can be conveniently attached to existing experiment chambers. The basic idea of the design is the use of fixed mounted gratings of diffent radii and groove densities and a big two-dimensional position sensitive detector mounted on a x−y angle table. The design is discussed in some detail and performance is presented.
Article
The phase equilibria in the ternary system titanium-aluminum-nitrogen are investigated for two isothermal sections. At 1273 K one encounters the H-phase Ti2AlN (a = 0.29912 nm, c = 1.3621 nm) and the cubic perovskite-type phase Ti3AlN (a = 0.41120 nm). At 1573 K one encounters additionally Ti3Al2N2 (space group: P31c, hexagonal axes a = 0.29875 nm, c = 2.3350 nm). α-Titanium dissolves nitrogen and aluminum to a large extent, but no solubility of the third element was detected in any of the other binary phases.
Article
The electronic structure of nanolaminate Ti2AlN and TiN thin films has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, N K, Al L1 and Al L2,3 emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Three different types of bond regions are identified; a relatively weak Ti 3d - Al 3p bonding between -1 and -2 eV below the Fermi level, and Ti 3d - N 2p and Ti 3d - N 2s bonding which are deeper in energy observed at -4.8 eV and -15 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states of Al L2,3 emission from Ti2AlN in comparison to pure Al metal is found, which reflects the Ti 3d - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic and crystal structures of Ti2AlN and TiN are discussed in relation to the intercalated Al layers of the former compound and the change of the materials properties in comparison to the isostructural carbides.
Article
From a theory of Hohenberg and Kohn, approximation methods for treating an inhomogeneous system of interacting electrons are developed. These methods are exact for systems of slowly varying or high density. For the ground state, they lead to self-consistent equations analogous to the Hartree and Hartree-Fock equations, respectively. In these equations the exchange and correlation portions of the chemical potential of a uniform electron gas appear as additional effective potentials. (The exchange portion of our effective potential differs from that due to Slater by a factor of 23.) Electronic systems at finite temperatures and in magnetic fields are also treated by similar methods. An appendix deals with a further correction for systems with short-wavelength density oscillations.
Article
The L2,3 X-ray emission of Cu metal has been measured using monochromatic synchrotron radiation. The self-absorption effect in the spectra is shown to be very small in our experimental geometry. From the quantitative analysis of spectra recorded at different excitation energies, the L3/L2 emission intensity ratio and the partial Auger-width are extracted. High-energy satellite features on the L3 emission line are separated by a subtraction procedure. The satellite intensity is found to be slowly increasing for excitation energies between the L3, L2 and L1 core-level thresholds due to shake-up and shake-off transitions. As the excitation energy passes the L2 threshold, a step of rapidly increasing satellite intensity of the L3 emission is found due to additional Coster-Kronig processes.
Article
The electronic structure of the heavy fermion compound CeB6 is probed by resonant inelastic soft X-ray scattering using photon energies across the Ce 3d and 4d absorption edges. The hybridization between the localized 4f orbitals and the delocalized valence-band states is studied by identifying the different spectral contributions from inelastic Raman scattering and normal fluorescence. Pronounced energy-loss structures are observed below the elastic peak at both the 3d and 4d thresholds. The origin and character of the inelastic scattering structures are discussed in terms of charge-transfer excitations in connection to the dipole allowed transitions with 4f character. Calculations within the single impurity Anderson model with full multiplet effects are found to yield consistent spectral functions to the experimental data.
Article
Resonant soft X-ray Raman scattering measurements on NiO have been made at photon energies across the Ni 2p absorption edges. The details of the spectral features are identified as Raman scattering due to d-d and charge-transfer excitations. The spectra are interpreted within the single impurity Anderson model, including multiplets, crystal-field and charge-transfer effects. At threshold excitation, the spectral features consists of triplet-triplet and triplet-singlet transitions of the 3d8 configuration. For excitation energies corresponding to the charge-transfer region in the Ni 2p X-ray absorption spectrum of NiO, the emission spectra are instead dominated by charge-transfer transitions to the 3d9L-1 final state. Comparisons of the final states with other spectroscopical techniques are also made.
Article
We report resonant inelastic x-ray scattering (RIXS) excited by circularly polarized x-rays on Mn-Zn ferrite at the Mn L2,3-resonances. We demonstrate that crystal field excitations, as expected for localized systems, dominate the RIXS spectra and thus their dichroic asymmetry cannot be interpreted in terms of spin-resolved partial density of states, which has been the standard approach for RIXS dichroism. We observe large dichroic RIXS at the L2-resonance which we attribute to the absence of metallic core hole screening in the insulating Mn-ferrite. On the other hand, reduced L3-RIXS dichroism is interpreted as an effect of longer scattering time that enables spin-lattice core hole relaxation via magnons and phonons occurring on a femtosecond time scale.
Article
Unoccupied energy bands of iron are mapped by inverse photoemission from Fe(100), Fe(110), and Fe(111). The ferromagnetic exchange splitting deltaEex of the uppermost d band is measured for the H'25 point, where the minority- and majority-spin subbands are both empty (deltaEex=1.8 eV with H'25↓ at 1.9 eV and H'25↑ at 0.12 eV above EF). Several other critical points are determined, such as the minority-spin Gamma12 and P3 points, the majority-spin N3 point, and the higher-lying H15,H1 points of s,p character. Critical points and exchange splitting are compared with first-principles, local-density calculations. The real part of the self-energy is obtained from this comparison, and the imaginary part by measuring the liftime broadening. In the d-band region, the self-energy causes a 10% compression of the bands and a linear broadening Gamma(E)~0.6\|E-EF\|.
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