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At least 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on CeCoGe2 by Materials Project

CeCoGe2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ce is bonded in a 10-coordinate geometry to four equivalent Co and ten Ge atoms. All Ce–Co bond lengths are 3.19 Å. There are a spread of Ce–Ge bond distances ranging from 3.12–3.31 Å. Co is bonded in a 5-coordinate geometry to four equivalent Ce and five Ge atoms. There are a spread of Co–Ge bond distances ranging from 2.28–2.40 Å. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 1-coordinate geometry to six equivalent Ce, one Co, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.55 Å. In the second Ge site, Ge is bonded in a 8-coordinate geometry to four equivalent Ce and four equivalent Co atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeGa2Cu3 by Materials Project

CeCu3Ga2 crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. Ce is bonded in a 6-coordinate geometry to ten Cu and eight equivalent Ga atoms. There are a spread of Ce–Cu bond distances ranging from 2.99–3.38 Å. All Ce–Ga bond lengths are 3.33 Å. There are two inequivalent Cu sites. In the first Cu site, Cu is bonded to four equivalent Ce, four equivalent Cu, and four equivalent Ga atoms to form distorted CuCe4Ga4Cu4 cuboctahedra that share corners with eight equivalent CuCe4Ga4Cu4 cuboctahedra, corners with eight equivalent GaCe4Ga2Cu6 cuboctahedra, edges with two equivalent CuCe4Ga4Cu4 cuboctahedra, edges with eight equivalent GaCe4Ga2Cu6 cuboctahedra, faces with two equivalent CuCe4Ga4Cu4 cuboctahedra, and faces with eight equivalent GaCe4Ga2Cu6 cuboctahedra. All Cu–Cu bond lengths are 2.55 Å. All Cu–Ga bond lengths are 2.59 Å. In the second Cu site, Cu is bonded in a 12-coordinate geometry to three equivalent Ce, two equivalent Cu, and four equivalent Ga atoms. All Cu–Ga bond lengths are 2.60 Å. Ga is bonded to four equivalent Ce, six Cu, and two equivalent Ga atoms to form GaCe4Ga2Cu6 cuboctahedra that share corners with four equivalent CuCe4Ga4Cu4 cuboctahedra, corners with twelve equivalent GaCe4Ga2Cu6 cuboctahedra, edges with four equivalent CuCe4Ga4Cu4 cuboctahedra, edges with six equivalent GaCe4Ga2Cu6 cuboctahedra, faces with four equivalent CuCe4Ga4Cu4 cuboctahedra, and faces with six equivalent GaCe4Ga2Cu6 cuboctahedra. Both Ga–Ga bond lengths are 2.65 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce2In8Pt by Materials Project

Ce2PtIn8 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ce is bonded to twelve In atoms to form CeIn12 cuboctahedra that share corners with eight equivalent CeIn12 cuboctahedra, edges with twelve InCe4In8 cuboctahedra, faces with five equivalent CeIn12 cuboctahedra, and faces with eight InCe4In8 cuboctahedra. There are a spread of Ce–In bond distances ranging from 3.25–3.35 Å. Pt is bonded in a body-centered cubic geometry to eight equivalent In atoms. All Pt–In bond lengths are 2.81 Å. There are four inequivalent In sites. In the first In site, In is bonded in a 4-coordinate geometry to two equivalent Ce, two equivalent Pt, and two equivalent In atoms. Both In–In bond lengths are 3.26 Å. In the second In site, In is bonded to four equivalent Ce and eight In atoms to form distorted InCe4In8 cuboctahedra that share corners with four equivalent InCe4In8 cuboctahedra, edges with eight equivalent CeIn12 cuboctahedra, edges with eight equivalent InCe4In8 cuboctahedra, faces with four equivalent CeIn12 cuboctahedra, and faces with twelve InCe4In8 cuboctahedra. There are four shorter (3.34 Å) and four longer (3.35 Å) In–In bond lengths. In the third In site, In is bonded to four equivalent Ce and eight In atoms to form distorted InCe4In8 cuboctahedra that share corners with four equivalent InCe4In8 cuboctahedra, edges with eight equivalent CeIn12 cuboctahedra, edges with eight equivalent InCe4In8 cuboctahedra, faces with four equivalent CeIn12 cuboctahedra, and faces with twelve InCe4In8 cuboctahedra. All In–In bond lengths are 3.34 Å. In the fourth In site, In is bonded to four equivalent Ce and eight In atoms to form distorted InCe4In8 cuboctahedra that share corners with eight equivalent InCe4In8 cuboctahedra, edges with four equivalent CeIn12 cuboctahedra, edges with eight InCe4In8 cuboctahedra, faces with four equivalent CeIn12 cuboctahedra, and faces with nine InCe4In8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrCe3 by Materials Project

SrCe3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Sr is bonded to twelve equivalent Ce atoms to form SrCe12 cuboctahedra that share corners with twelve equivalent SrCe12 cuboctahedra, edges with twenty-four equivalent CeSr4Ce8 cuboctahedra, faces with six equivalent SrCe12 cuboctahedra, and faces with twelve equivalent CeSr4Ce8 cuboctahedra. All Sr–Ce bond lengths are 3.58 Å. Ce is bonded to four equivalent Sr and eight equivalent Ce atoms to form CeSr4Ce8 cuboctahedra that share corners with twelve equivalent CeSr4Ce8 cuboctahedra, edges with eight equivalent SrCe12 cuboctahedra, edges with sixteen equivalent CeSr4Ce8 cuboctahedra, faces with four equivalent SrCe12 cuboctahedra, and faces with fourteen equivalent CeSr4Ce8 cuboctahedra. All Ce–Ce bond lengths are 3.58 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeAl3Au by Materials Project

CeAuAl3 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ce is bonded in a 8-coordinate geometry to four equivalent Au and twelve Al atoms. All Ce–Au bond lengths are 3.40 Å. There are a spread of Ce–Al bond distances ranging from 3.21–3.57 Å. Au is bonded in a 5-coordinate geometry to four equivalent Ce and five Al atoms. There are one shorter (2.46 Å) and four longer (2.55 Å) Au–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a distorted single-bond geometry to four equivalent Ce and one Au atom. In the second Al site, Al is bonded in a distorted bent 120 degrees geometry to four equivalent Ce and two equivalent Au atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeAlCu by Materials Project

CeCuAl crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Ce is bonded in a 5-coordinate geometry to five Cu and six equivalent Al atoms. There are four shorter (2.96 Å) and one longer (2.97 Å) Ce–Cu bond lengths. There are two shorter (3.22 Å) and four longer (3.30 Å) Ce–Al bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu is bonded in a distorted q6 geometry to three equivalent Ce and six equivalent Al atoms. All Cu–Al bond lengths are 2.63 Å. In the second Cu site, Cu is bonded in a 9-coordinate geometry to six equivalent Ce and three equivalent Al atoms. All Cu–Al bond lengths are 2.80 Å. Al is bonded to six equivalent Ce, four Cu, and two equivalent Al atoms to form a mixture of distorted face, edge, and corner-sharing AlCe6Al2Cu4 cuboctahedra. Both Al–Al bond lengths are 2.82 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeMg by Materials Project

CeMg crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Mg is bonded to nine equivalent Mg and three equivalent Ce atoms to form MgCe3Mg9 cuboctahedra that share corners with six equivalent MgCe3Mg9 cuboctahedra, corners with twelve equivalent CeCe9Mg3 cuboctahedra, edges with six equivalent CeCe9Mg3 cuboctahedra, edges with twelve equivalent MgCe3Mg9 cuboctahedra, faces with eight equivalent CeCe9Mg3 cuboctahedra, and faces with twelve equivalent MgCe3Mg9 cuboctahedra. There are six shorter (3.15 Å) and three longer (3.22 Å) Mg–Mg bond lengths. All Mg–Ce bond lengths are 3.44 Å. Ce is bonded to three equivalent Mg and nine equivalent Ce atoms to form CeCe9Mg3 cuboctahedra that share corners with six equivalent CeCe9Mg3 cuboctahedra, corners with twelve equivalent MgCe3Mg9 cuboctahedra, edges with six equivalent MgCe3Mg9 cuboctahedra, edges with twelve equivalent CeCe9Mg3 cuboctahedra, faces with eight equivalent MgCe3Mg9 cuboctahedra, and faces with twelve equivalent CeCe9Mg3 cuboctahedra. There are six shorter (3.15 Å) and three longer (3.61 Å) Ce–Ce bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Probing Multiconfigurational States by Spectroscopy: The Cerium XAS L 3 ‐edge Puzzle

Abstract The Ce L 3 edge XAS spectra of CeO 2 and cerocene [Ce(C 8 H 8 ) 2 ] were calculated with relativistic ab‐initio multireference wavefunction approaches capable of reproducing the observed spectra accurately. The study aims to resolve the decades‐long puzzle regarding the relationship between the number and relative intensities of the XAS peaks and the 4f electron occupation in the ground state (GS) versus the core‐excited states (ESs). CeO 2 and cerocene exemplify the different roles of covalent bonding and wavefunction configurational composition in the observed intensity patterns. Good agreement is found between the calculated GS 4f‐shell occupations and the value derived from XAS measurements using peak areas ( n f ). The identity of the two‐peaked Ce L 3 edge is fully rationalized from the perspective of the relaxed wavefunctions for the GS and core ESs. The states underlying the different peaks differ from each other in a surprisingly simple way that can be associated with 4f 1 vs. 4f 0 sub‐configurations. Furthermore, part of one of the cerocene spectral peaks is associated with 4f 2 sub‐configurations. The pattern therefore reveals excited states that can be interpreted in terms of Ce IV and III oxidation numbers, as long assumed, with Ce II states additionally appearing in the cerocene spectrum. While this work demonstrates the rough accuracy of the conventional approach to determining n f from Ce L 3 ‐edge XAS, limitations are highlighted in terms of the ultimate accuracy of this approach and the potential of observing new types of excited states. The need to determine the sources of n f by calculations, is stressed.

Sergentu, Dumitru‐Claudiu↗
DOE OSTI2024

Advancements in cerium/titanium metal-organic frameworks: Unparalleled stability in CO oxidation

Due to the excellent catalytic properties of Ce-based materials, the development of thermally stable metal-organic frameworks (MOFs) based on Ce-oxo clusters has attracted significant attention but remains challenging. In this work, we report the synthesis of an unreported Ce 4 Ti 2 -TMA (Ce IV 4 Ti IV 2 O 4 (OH) 4 (C(CH 3 ) 3 COO) 12 ·3H 2 O·3MeCN) cluster, which serves as an ideal source for the assembly of robust Ce/Ti-MOFs. Using this cluster, we constructed two isostructural MOFs, denoted as NU-3000 and NU-3001. Single-crystal X-ray diffraction analysis confirms these MOFs as mesoporous structures with 12-coordinated Ce 3 Ti 3 nodes. Furthermore, structural analysis reveals a plane triangular node structure that likely contributes to the excellent thermal stability of these MOFs. Finally, both MOFs show catalytic activity toward high-temperature (250°C) CO oxidation and maintain significant porosity, emphasizing the thermal stability of these materials under practical catalytic conditions. Furthermore, the straightforward synthesis of thermally robust Ce/Ti-MOFs from the Ce 4 Ti 2 -TMA cluster will pave the way for future Ce/Ti-MOF-based catalyst development.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Circular economy pathways for decarbonizing aluminum and steel automotive body sheet components in the United States

Decarbonizing vehicle production is essential to reducing automotive sector emissions. This study quantifies greenhouse gas (GHG) emissions from aluminum and steel auto-body sheet components produced in the US. It evaluates the effectiveness of circular economy (CE) strategies (greater closed-loop recycling of pre-consumer scrap, post-consumer scrap, and increased manufacturing yields) to reduce supply chain emissions across different process technology and electricity grid decarbonization pathways. We combine dynamic material flow analysis (2025–2050) with cradle-to-gate life-cycle modeling to assess production emissions and the potential reductions associated with the CE strategies under frozen, moderate, and aggressive technology and grid decarbonization scenarios. Current emissions intensities are estimated at approximately 12.3 kg.CO₂eq/kg of aluminum and 4.3 kg.CO₂eq/kg of steel sheet embedded in the vehicle. Under the frozen decarbonization scenario and current levels of circularity, annual emissions attributable to US aluminum and steel auto-body sheet supply chains could rise by 54 % and 18 % respectively by 2050. Rapid deployment of the CE strategies can cut these annual emissions in 2050 by 52 % for aluminum and 44 % for steel. However, scrap quality constraints lead to saturation points, limiting these benefits unless addressed. Aggressive deployment of low-carbon production technologies and a low-carbon grid reduces the relative benefit of implementing the CE strategies; however, even under the aggressive technology and grid decarbonization scenario, the CE strategies reduce annual emissions by a further 23 %-54 % by 2050. These findings highlight the urgent need to integrate CE strategies into the sheet metal supply chain to support decarbonization efforts and help meet climate targets.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Kinetic stability of Chapman–Enskog plasmas

In this paper, we investigate the kinetic stability of classical, collisional plasma – that is, plasma in which the mean-free-path $\lambda$ of constituent particles is short compared with the length scale $L$ over which fields and bulk motions in the plasma vary macroscopically, and the collision time is short compared with the evolution time. Fluid equations are typically used to describe such plasmas, since their distribution functions are close to being Maxwellian. The small deviations from the Maxwellian distribution are calculated via the Chapman–Enskog (CE) expansion in $\lambda /L \ll 1$ , and determine macroscopic momentum and heat fluxes in the plasma. Such a calculation is only valid if the underlying CE distribution function is stable at collisionless length scales and/or time scales. We find that at sufficiently high plasma $\beta$ , the CE distribution function can be subject to numerous microinstabilities across a wide range of scales. For a particular form of the CE distribution function arising in strongly magnetised plasma ( viz. plasma in which the Larmor periods of particles are much smaller than collision times), we provide a detailed analytic characterisation of all significant microinstabilities, including peak growth rates and their associated wavenumbers. Of specific note is the discovery of several new microinstabilities, including one at sub-electron-Larmor scales (the ‘whisper instability’) whose growth rate in certain parameter regimes is large compared with other instabilities. Our approach enables us to construct the kinetic stability maps of classical, two-species collisional plasma in terms of $\lambda$ , the electron inertial scale $d_e$ and the plasma $\beta$ . This work is of general consequence in emphasising the fact that high- $\beta$ collisional plasmas can be kinetically unstable; for strongly magnetised CE plasmas, the condition for instability is $\beta \gtrsim L/\lambda$ . In this situation, the determination of transport coefficients via the standard CE approach is not valid.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Hybrid Sorbents for 129 I Capture from Contaminated Groundwater

Radioiodine ( 129 I) poses a risk to the environment due to its long half-life, toxicity, and mobility. It is found at the U.S. Department of Energy Hanford Site due to legacy releases of nuclear wastes to the subsurface where 129 I is predominantly present as iodate (IO 3 – ). To date, a cost-effective and scalable cleanup technology for 129 I has not been identified, with hydraulic containment implemented as the remedial approach. Here, novel high-performing sorbents for 129 I remediation with the capacity to reduce 129 I concentrations to or below the US Environmental Protection Agency (EPA) drinking water standard and procedures to deploy them in an ex-situ pump and treat (P&T) system are introduced. Furthermore, this includes implementation of hybridized polyacrylonitrile (PAN) beads for ex-situ remediation of IO 3 – -contaminated groundwater for the first time. Iron (Fe) oxyhydroxide and bismuth (Bi) oxyhydroxide sorbents were deployed on silica substrates or encapsulated in porous PAN beads. In addition, Fe–, cerium (Ce)–, and Bi–oxyhydroxides were encapsulated with anion-exchange resins. The PAN–bismuth oxyhydroxide and PAN–ferrihydrite composites along with Fe- and Ce-based hybrid anion-exchange resins performed well in batch sorption experiments with distribution coefficients for IO 3 – of >1000 mL/g and rapid removal kinetics. Of the tested materials, the Ce-based hybrid anion-exchange resin was the most efficient for removal of IO 3 – from Hanford groundwater in a column system, with 50% breakthrough occurring at 324 pore volumes. The functional amine groups on the parent resin and amount of active sorbent in the resin can be customized to improve the iodine loading capacity. These results highlight the potential for IO 3 – remediation by hybrid sorbents and represent a benchmark for the implementation of commercially available materials to meet EPA standards for cleanup of 129 I in a large-scale P&T system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Cerium Dimer Anion and the Contribution of 4f Electrons to Lanthanide Metal–Metal Bonds

Direct metal−metal bonding between lanthanide atoms has been challenging to observe. We report on the first spectroscopic characterization of the cerium dimer anion (Ce 2 − ) and its neutral analog (Ce 2 ) in the gas phase, achieved using photoelectron and ultrafast spectroscopy combined with high-level quantum chemistry calculations. The electron affinity of Ce 2 is 0.24 eV, from which a dissociation energy of 2.21 eV is derived for Ce 2 − . The wave-packet dynamics upon photodetachment are studied and yield vibrational frequencies for electronically excited Ce 2 . Ce 2 − exhibits a conventional metal−metal triple bond with minimal contribution from 4f electrons. However, evidence of 4f-electron participation in bonding is identified for the low-energy excited states only 0.1 eV higher. The results challenge the assumption of inert 4f electrons in metal−metal bonding, and we propose a promising strategy for forming stable lanthanide−lanthanide bonds involving significant 4f-electron contributions.

Anions↗
DOE OSTI2021

Mechanistic insight into copper cation exchange in cadmium selenide semiconductor nanocrystals using X-ray absorption spectroscopy

In terms of producing new advances in sustainable nanomaterials, cation exchange (CE) of post-processed colloidal nanocrystals (NCs) has opened new avenues towards producing non-toxic energy materials via simple chemical techniques. The main processes governing CE can be explained by considering hard/soft acid/base theory, but the detailed mechanism of CE, however, has been debated and has been attributed to both diffusion and vacancy processes. In this work, we have performed in situ x-ray absorption spectroscopy to further understand the mechanism of the CE of copper in solution phase CdSe NCs. The x-ray data indicates clear isosbestic points, suggestive of cooperative behavior as previously observed via optical spectroscopy. Examination of the extended x-ray absorption fine structure data points to the observation of interstitial impurities during the initial stages of CE, suggesting the diffusion process is the fundamental mechanism of CE in this system.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Design principles of heterointerfacial redox chemistry for highly reversible lithium metal anode

High electrochemical reversibility is required for the application of high-energy-density lithium (Li) metal batteries; however, inactive Li formation and SEI (solid electrolyte interface)-instability-induced electrolyte consumption cause low Coulombic efficiency (CE). The prior interfacial chemical designs in terms of alloying kinetics have been used to enhance the CE of Li metal anode; however, the role of its redox chemistry at heterointerfaces remains a mystery. Herein, the relationship between heterointerfacial redox chemistry and electrochemical transformation reversibility is investigated. It is demonstrated that the lower redox potential at heterointerface contributes to higher CE, and this enhancement in CE is primarily due to the regulation of redox chemistry to Li deposition behavior rather than the formation of SEI films. Low oxidation potential facilitates the formation of the surface with the highly electrochemical binding feature after Li stripping, and low reduction potential can maintain binding ability well during subsequent Li plating, both of which homogenize Li deposition and thus optimize CE. In particular, Mg hetero-metal with ultra-low redox potential enables Li metal anode with significantly improved CE (99.6%) and stable cycle life for 700 cycles at 3.0 mA cm -2 . This work provides insight into the heterointerfacial design principle of next-generation negative electrodes for highly reversible metal batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Bipolar planetary nebulae from outflow collimation by common envelope evolution

ABSTRACT The morphology of bipolar planetary nebulae (PNe) can be attributed to interactions between a fast wind from the central engine and the dense toroidal-shaped ejecta left over from common envelope (CE) evolution. Here we use the 3D hydrodynamic adaptive mesh refinement (AMR) code AstroBEAR to study the possibility that bipolar PN outflows can emerge collimated even from an uncollimated spherical wind in the aftermath of a CE event. The output of a single CE simulation via the smoothed particle hydrodynamics (SPH) code phantom serves as the initial conditions. Four cases of winds, all with high enough momenta to account for observed high momenta pre-PN outflows, are injected spherically from the region of the CE binary remnant into the ejecta. We compare cases with two different momenta and cases with no radiative cooling versus application of optically thin emission via a cooling curve to the outflow. Our simulations show that in all cases highly collimated bipolar outflows result from deflection of the spherical wind via the interaction with the CE ejecta. Significant asymmetries between the top and bottom lobes are seen in all cases. The asymmetry is strongest for the lower momentum case with radiative cooling. While real post-CE winds may be aspherical, our models show that collimation via ‘inertial confinement’ will be strong enough to create jet-like outflows even beginning with maximally uncollimated drivers. Our simulations reveal detailed shock structures in the shock-focused inertial confinement (SFIC) model and develop a lens-shaped inner shock that is a new feature of SFIC-driven bipolar lobes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Singly occupied 4⁢𝑓 antiferromagnetic insulators: CePO 4 and CeVO 4

Rare-earth containing wide band gap oxides, which provide spin-photon interface and narrow linewidth optical emission, are getting significant attention as the most promising candidate materials in advancing quantum transduction and memories. Here, in this work, from ab initio calculations, we identify antiferromagnetic ground states in structurally preferred monoclinic CePO 4 and tetragonal CeVO 4 exhibiting localized occupied and unoccupied Ce 4⁢𝑓 states with 4⁢𝑓−4⁢𝑓 transition characteristics. Interestingly, in CePO 4 , O 2⁢𝑝 and P 3⁢𝑝 states hybridize negligibly with Ce 4⁢𝑓 states, while in CeVO 4 , V 3⁢𝑑 and O 2⁢𝑝 states hybridize and appear as extended states in between the occupied and unoccupied Ce 4⁢𝑓 states. Here, phonon calculations and analysis identify and differentiate Raman active phonon modes along with the spin phonon coupling of Ce in both CePO 4 and CeVO 4 that ultimately lead to different 4⁢𝑓 ground-state crystal-field multiplets, which are critical to accurately describe electronic transitions for foundational quantum transduction and memories. Further, the identified 𝐶 1 site symmetry of Ce, lacking inversion symmetry in CePO 4 , is relevant for quantum memories and 𝐷 2⁢𝑑 site symmetry of Ce exhibiting inversion symmetry in CeVO 4 is relevant for quantum transduction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electronic structures and pseudogap nature of the strongly correlated Kondo semimetals and insulators CeNiSn and CeRhX(X=As, Sb)

Employing temperature (T)-dependent angle-resolved photoemission spectroscopy (ARPES) near the Ce 4d absorption edge, we have investigated the electronic structures of the strongly correlated Kondo insulators (KIs) and/or Kondo semimetals of CeNiSn and CeRhX (X=As, Sb), which also belong to potential topological KIs (TKIs). Good agreement is found between the Fermi surfaces (FSs) measured at the Ce 4d→4f on resonance and those calculated and unfolded into the Ce-only Brillouin zone, supporting the crucial Ce 4f contribution to the Fermi-edge states in them. While the FSs of CeRhSb and CeNiSn are similar to each other, they are quite different from those of CeRhAs, which is understood to originate from the semimetallic Kondo ground states of CeNiSn and CeRhSb in contrast to the insulating Kondo ground state of CeRhAs. T-dependent ARPES demonstrates the existence of the Kondo resonance above the Fermi level (EF) and its T-driven decoherence in CeNiSn and CeRhSb, and the existence of the Ce 4f Kondo-like peak well below EF with a pseudogap in CeRhAs. With increasing T, the tail of the Kondo resonance in CeNiSn and CeRhSb loses its coherence, whereas the Ce 4f Kondo-like peak in CeRhAs persists up to T≥200 K. The Kondo temperatures (TKs) are estimated via the analysis of T-dependent ARPES, yielding TK≈80 K (CeNiSn), TK≈180 K (CeRhSb), and TK≫200 K (CeRhAs). High-resolution, low-T ARPES confirms the Kondo resonance just above EF in CeNiSn and CeRhSb Kondo semimetals and the KI ground state of CeRhAs with a pseudogap of Δ≈30 meV, demonstrating the importance of the coherent Kondo states in determining their potential topological properties. The differences in the T-dependent ARPES of CeNiSn and CeRhSb suggest the weaker f-c hybridization in CeNiSn than in CeRhSb (c: conduction electron), which is likely due to the more localized Ni 3d orbitals than the delocalized Rh 4d orbitals. The differences between the T-dependent ARPES of CeNiSn/CeRhSb Kondo semimetals and those of CeRhAs Kondo insulator are likely due to the smaller volume of CeRhAs than those of CeNiSn/CeRhSb.

Kang, J-S↗