Se Chains Research Articles

Ultralow thermal conductivity and high thermoelectric performance induced by dimensionality reduction in chain-like compounds X2PtSe2 (X=K, rb)

Balancing low lattice thermal conductivity (κL) with a high power factor is a major challenge in the research of thermoelectric (TE) materials. In this paper, we report on a class of chain-like compounds, X2PtSe2(X = K, Rb), characterized by strong lattice anharmonicity, weak bonds, and low phonon group velocities. Using first-principles calculations in conjunction with self-consistent phonon theory and the Boltzmann transport equation, we systematically investigate the thermal and electrical transport properties of X2PtSe2(X = K, Rb). At room temperature, the κL of K2PtSe2 and Rb2PtSe2 in the direction perpendicular to the Pt–Se chains is only 0.15 and 0.10 Wm−1K−1, respectively. Additionally, due to the low-dimensional nature of the Pt–Se chains, these compounds exhibit a ‘pudding-mold type’ band structure, contributing to a TE power factor. At 300K, under n-type doping, K2PtSe2 and Rb2PtSe2 achieve TE figures of merit (ZT) values of 1.66 and 1.67, respectively, in the direction perpendicular to the Pt–Se chains. At 500K, the ZT value of Rb2PtSe2 approaches 4, far surpassing traditional TE materials. These results indicate that the chain-like compounds X2PtSe2(X = K, Rb) exhibit excellent TE performance, achieving energy conversion efficiencies comparable to commercial transducer devices.

Tailoring Se-rich glassy arsenoselenides employing the nanomilling platform

By XRPD analysis related to diffuse peak-halos in Se-rich glassy AsxSe100-x, the high-energy nanomilling driven reamorphization in these substances is recognized as molecular-to-network transformations of Se chains bridging cation polyhedrons (like AsSe3/2 pyramids) from preferential cis- to trans-configurated topology. At the medium-range structure, the process of reamorphization is revealed as enhancement in the intermediate-range ordering of these glasses due to high-angular shifted and broadened first sharp diffraction peak (FSDP) accompanied by suppression in extended-range ordering due to high-angular shifted but narrowed principal diffraction peak (PDP), so that peak-halos become more distinguishable after nanomilling. Principal trend in the XRPD patterns of glassy arsenoselenides with growing Se content is revealed as suppression in intermediate-range ordering accompanied by enhancement in extended-range ordering, resulting in more overlapped peak-halos. Irregular sequence of randomly distributed cis- and trans-configurated linkages in Se-rich g-AsxSe100-x is visualized by ab initio quantum-chemical modeling of molecular and chain-like network clusters.

Structures of Se chains encapsulated in single-walled carbon nanotubes

In this study, the structures of two Se chains confined inside single-walled carbon nanotubes (SWCNTs), which were denoted as Se@SWCNT, were investigated by extended X-ray absorption fine structure analysis and transmission electron microscopy. The Se chains were linear and parallel to each other in the SWCNTs. The covalent bond length of Se@SWCNT was shorter than that of trigonal Se (t-Se), whereas the force constant was larger, thereby suggesting that the covalent bond was stronger for Se@SWCNT than that for t-Se. The interchain interaction originated from the overlap of lone-pair and antibonding orbitals on adjacent chains, so the disappearance of the overlap in the encapsulated Se chains strengthened the covalent bonds.

Optoelectronic Manifestation of Orbital Angular Momentum Driven by Chiral Hopping in Helical Se Chains.

Chiral materials have garnered significant attention in the field of condensed matter physics. Nevertheless, the magnetic moment induced by the chiral spatial motion of electrons in helical materials, such as elemental Te and Se, remains inadequately understood. In this work, we investigate the development of quantum angular momentum enforced by chirality by using static and time-dependent density functional theory calculations for an elemental Se chain. Our findings reveal the emergence of an unconventional orbital texture driven by the chiral geometry, giving rise to a nonvanishing current-induced orbital moment. By incorporating spin-orbit coupling, we demonstrate that current-induced spin accumulation arises in the chiral chain, which fundamentally differs from the conventional Edelstein effect. Furthermore, we demonstrate optoelectronic detection of the orbital angular momentum in the chiral Se chain, providing an alternative to the interband Berry curvature, which is ill-defined in low dimensions.

Thermodynamic heat-transfer phenomena in nanostructured glassy substances: a comparative study on g-As5Se95 and g-As55Se45

Nanostructurization-driven responses in calorimetric heat-transfer phenomena are compared for glassy arsenoselenides at different levels of their molecular network organization, namely in high-polymerized g-As5Se95 and low-polymerized g-As55Se45, employing multifrequency temperature-modulated DSC-TOPEM® method complemented with Raman scattering microspectroscopy. It is shown that high-polymerized network composed of AsSe3 pyramids interlinked by Se chains with small number of Se8 molecular units decoupled from this network prevails in melt-quenched and nanomilling-derived g-As5Se95. Transition to more polymerized network due to incorporation of destroyed Se8 molecules into glass backbone occurs in this glass under nanostructurization. As a result, nanostructurization-driven calorimetric response in g-As5Se95 dominates by size-induced glass-transition temperature depression. The low-polymerized structure of g-As55Se45 is built of As–Se network enriched with tetra-arsenic selenide molecular units decoupled from this network. Molecular-to-network transition owing to nanomilling-driven destruction of these cage molecules and their incorporation into newly polymerized glass-forming backbone occurs in g-As55Se45 resulting in strong increase in calorimetric glass-transition temperature.

Advanced all-solid-state lithium-selenium batteries enabled by selenium-nitrogen doped hierarchic meso-microporous carbon nanospheres composite cathode

Selenium, an element belonging to the same group in the periodic table as sulfur, has a high electronic conductivity (1 × 10−5 S/cm) and a high volumetric energy density (3253 mAh/cm3), which is a prospective cathode material for high-energy all-solid-state rechargeable batteries. However, its wide use is hindered by large volume expansion and low utilization rate. In this work, Se-infused nitrogen-doped hierarchical meso-microporous carbon composites (Se/NHPC) are prepared by a melt-diffusion process. Amorphous Se is uniformly dispersed in meso-micropores of NHPC with a high mass loading of 81%. All-solid-state Li-Se batteries fabricated by using Se/NHPC as the cathode, a Li-In alloy as the anode, and Li6PS5Cl as the solid-state electrolyte, deliver a highly reversible capacity of 621 mAh/g (92% of theoretical capacity), a good rate capability and a high capacity retention value of 80.9% after 100 cycles. It is found that the capacity decay of Se cathode is mainly related to the interfacial degradation and the separation of Se from the carbon substrate, as suggested by the continuous increase of interfacial resistance and the structural transformation from amorphous Sen chains to Se8 rings initial discharge/charge cycle and then to the trigonally crystalline Se chains structure after the long-term cycles.

Pressure-induced YSe3 and Y3Se with charming structures and properties

The preparation of unconventional stoichiometric compounds provides an opportunity to access new chemistry, physics, and applications. Herein, several new Y-Se compounds (e.g., YSe3, Y3Se2, and Y3Se) are disclosed through first-principles structural search calculations under high pressure. YSe3 consists of a linear Se chain with one-electron two-center bonding character, which is mainly responsible for the superconductivity. In contrast, Y3Se, in which part of electrons of Y atom are located in the hollow Y6 octahedra, combines electride with superconductivity, adding a new member to the family of pressurized superconducting electrides. On the other hand, pressure-induced YS3 and Y3S are isostructural to YSe3 and Y3Se, respectively, but the critical temperature of YS3 is much higher than YSe3, and becomes inverse for Y3S and Y3Se, providing a chance to enrich insight into the relationship between atomic arrangement and chemical composition.

Raman and optical absorption spectra of oriented Se8 and Se12 rings formed in zeolites: Dependence on the Se loading density

We encapsulated selenium (Se) into AFI and LTA zeolites via Se vapour adsorption at ∼450 °C and studied Raman and optical absorption spectra (RS and OAS, respectively) of zeolite single crystals with incorporated Se. At high Se loading density (D), Se8 rings are formed in the AFI channels along with Se chains. The rings are oriented by their 4-fold axis parallel to channels. Se8 is also formed in the LTA large cavities with its 4-fold axis oriented parallel to the 4-fold axis of LTA at any D up to ∼8 Se atoms per cavity (at/c). However, at D > 0.5 at/c, nearly unexplored Se12 rings oriented by their 3-fold axis parallel to the LTA 3-fold axis are formed along with Se8 in neighboring cavities. We discriminate between Se8 and Se12 rings via 1) RS frequencies; 2) RS and OAS band intensities vs. D; 3) RS band intensities vs. excitation wavelength and light polarization configuration. With an increase in D, the number of Se12 rings grows faster than that of Se8. We extract OAS of Se8 and Se12 from the experimental AFI-Se and LTA-Se OAS and show that the 3.0–3.3 eV absorption of Se12 is enhanced compared to that of Se8. This absorption is responsible for the observed resonant Raman effect of Se12 at the 514.5 nm wavelength excitation. Both LTA-confined Se8 and Se12 display rather high thermal stability.

Beyond-mean-field dynamical correlations for nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum * *Supported by the National Natural Science Foundation of China (11875225, 12005175, 11935003, 11875075, 11975031, 12070131001, 11790325), the Fundamental Research Funds for the Central Universities, the National Key R&D Program of China (2017YFE0116700, 2018YFA0404400), the State Key Laboratory of Nuclear Physics and Technology, Peking University (NPT2020ZZ01)

We extend the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) to go beyond-mean-field framework by performing a two-dimensional collective Hamiltonian. The influences of dynamical correlations on the ground-state properties are examined in different mass regions, picking Se, Nd, and Th isotopic chains as representatives. It is found that the dynamical correlation energies (DCEs) and the rotational correction energies in the cranking approximation have an almost equivalent effect on the description of binding energies for most deformed nuclei, and the DCEs can provide a significant improvement for the (near) spherical nuclei close to the neutron shells and thus reduce the rms deviations of by 17%. Furthermore, it is found that the DCEs are quite sensitive to the pairing correlations; taking Nd as an example, a 10% enhancement of pairing strength can raise the DCE by 37%.

The formation of a one-dimensional van der Waals selenium crystal from the three-dimensional amorphous phase: A spectroscopic signature of van der Waals bonding

Trigonal selenium is a prototypical one-dimensional (1D) van der Waals (vdW) solid, where covalently bonded helical chains are held together by weaker vdW forces. In this work, we have studied structural transformation from a three-dimensional amorphous phase of non-interacting Se chains into a 1D vdW crystal using x-ray absorption spectroscopy. The crystallization process and establishment of vdW interaction are accompanied by elongation and weakening of covalent Se-Se bonds. We have found a unique signature in the x-ray absorption near-edge structure spectrum that is associated with vdW bonds and can be used to identify the formation of the latter. We believe that a similar approach can be used to study other 1D vdW solids, such as transition-metal trichalcogenides, and particularly stress the usefulness of x-ray absorption spectroscopy to identify vdW bonds.

Structural control on the rheological behavior of binary P-Se supercooled liquids

The link between the atomic structure and the shear relaxation behavior of PxSe100-x (0≤x≤25) supercooled liquids is investigated using Raman spectroscopy and parallel plate rheometry. The P atoms in these glasses form Se=P(Se1/2)3, P(Se1/2)3 and 2/2SeP-PSe2/2 units, which serve as cross-linkers of the [Se]n chain segments. The frequency dependence of the storage and loss moduli as well as the relaxation spectra H(τ) indicate that liquids with >85% Se are characterized by the coexistence of a slow and a fast relaxation process corresponding to bond scission/renewal and Se chain segmental motion, respectively. On the other hand, liquids with ≤85% Se display only the bond scission/renewal process. The H(τ) spectra suggest that the relaxation-time τ distribution for Se chain dynamics is a sensitive function of the chain length, while that for bond scission/renewal is controlled by the variety of bond types and structural moieties involved.

Compressional origin of the Aegean Orogeny, Greece

The Aegean Sea area is thought to be an actively extending back-arc region, north of the present day Hellenic volcanic arc and north-dipping subduction zone in the Eastern Mediterranean. The area shows extensive normal faulting, ductile ‘extensional’ shear zones and extensional S-C fabrics throughout the islands that have previously been related to regional Aegean extension associated with slab rollback on the Hellenic Subduction Zone. In this paper, we question this interpretation, and suggest the Cenozoic geodynamic evolution of the Aegean region is associated with a Late Cretaceous–Eocene NE-dipping subduction zone that was responsible for continent-continent collision between Eurasia and Adria-Apulia/Cyclades. Exhumation of eclogite and blueschist facies rocks in the Cyclades and kyanite-sillimanite grade gneisses in the Naxos core complex have pressures that are far greater than could be accounted for purely by lithospheric extension and isostatic uplift. We identify four stages of crustal shortening that affected the region prior to regional lithospheric extension, herein called the Aegean Orogeny. This orogeny followed a classic Wilson cycle from early ophiolite obduction (ca. 74 Ma) onto a previously passive continental margin, to attempted crustal subduction with HP eclogite and blueschist facies metamorphism (ca. 54–45 ​Ma), through crustal thickening and regional kyanite – sillimanite grade Barrovian-type metamorphism (ca. 22–14 ​Ma), to orogenic collapse (<14 ​Ma). At least three periods of ‘extensional’ fabrics relate to: (1) Exhumation of blueschists and eclogite facies rocks showing tight-isoclinal folds and top-NE, base-SW fabrics, recording return flow along a subduction channel in a compressional tectonic setting (ca. 50–35 ​Ma). (2) Extensional fabrics within the core complexes formed by exhumation of kyanite- and sillimanite gneisses showing thrust-related fabrics at the base and ‘extensional’ fabrics along the top (ca. 18.5–14 ​Ma). (3) Regional ductile-brittle ‘extensional’ fabrics and low-angle normal faulting related to the North Cycladic Detachment (NCD) and the South(West) Cycladic Detachment (WCD) during regional extension along the flanks of a major NW–SE anticlinal fold along the middle of the Cyclades. Major low-angle normal faults and ductile shear zones show symmetry about the area, with the NE chain of islands (Andros, Tinos, Mykonos, Ikaria) exposing the NE-dipping NCD with consistent top-NE ductile fabrics along 200 ​km of strike. In contrast, from the Greek mainland (Attica) along the SE chain of islands (Kea, Kythnos, Serifos) a SW-dipping low-angle normal fault and ductile shear zone, the WCD is inferred for at least 100 ​km along strike. Islands in the middle of the Cyclades show deeper structural levels including kyanite- and sillimanite-grade metamorphic core complexes (Naxos, Paros) as well as Variscan basement rocks (Naxos, Ios). The overall structure is an ~100 ​km wavelength NW–SE trending dome with low-angle extensional faults along each flank, dipping away from the anticline axis to the NE and SW. Many individual islands show post-extensional large-scale folding of the low-angle normal faults around the domes (Naxos, Paros, Ios, Sifnos) indicating a post-Miocene late phase of E–W shortening.

Chlorine termination of selenium dangling bonds decreases tellurium-diffusion-induced acceptor states in hexagonal selenium

In this study, we examined the effects of doping chlorine (Cl) into crystalline selenium (c-Se) on diminishing the tellurium-diffusion-induced shallow acceptor states associated with the dangling bonds that appear at the ends of Se chains by theoretical analysis with the first-principles calculations. In this model, the negatively charged dangling bonds can be neutralized by inserting monovalent Cl atoms. Furthermore, the defect termination by doping Cl into fabricated Se thin films was experimentally demonstrated. Low-temperature cathodoluminescence measurements were implemented to show that acceptor-related emissions from the c-Se films were significantly decreased by Cl termination of the dangling bonds, experimentally confirming the results of the simulations.

Site-Specific Sodiation Mechanisms of Selenium in Microporous Carbon Host.

We combined advanced TEM (HRTEM, HAADF, EELS) with solid-state (SS)MAS NMR and electroanalytical techniques (GITT, etc.) to understand the site-specific sodiation of selenium (Se) encapsulated in a nanoporous carbon host. The architecture employed is representative of a wide number of electrochemically stable and rate-capable Se-based sodium metal battery (SMB) cathodes. SSNMR demonstrates that during the first sodiation, the Se chains are progressively cut to form an amorphous mixture of polyselenides of varying lengths, with no evidence for discrete phase transitions during sodiation. It also shows that Se nearest the carbon pore surface is sodiated first, leading to the formation of a core-shell compositional profile. HRTEM indicates that the vast majority of the pore-confined Se is amorphous, with the only localized presence of nanocrystalline equilibrium Na2Se2 (hcp) and Na2Se (fcc). A nanoscale fracture of terminally sodiated Na-Se is observed by HAADF, with SSNMR, indicating a physical separation of some Se from the carbon host after the first cycle. GITT reveals a 3-fold increase in Na+ diffusivity at cycle 2, which may be explained by the creation of extra interfaces. These combined findings highlight the complex phenomenology of electrochemical phase transformations in nanoconfined materials, which may profoundly differ from their "free" counterparts.

Ordering on different length scales in liquid and amorphous materials

The ordering on different real-space length scales is considered for a variety of glass-forming materials, ranging from densely packed amorphous metals and hard-sphere glassy colloids, to simple tetrahedral systems that include amorphous silicon and patchy colloids, to decorated tetrahedral systems that include amorphous ice and network-forming glasses with the AX2 stoichiometry (A = Si, Ge or Zn; X = O, S, Se or Cl). The ordering manifests itself as distinct peaks in the total structure factor , where k denotes the magnitude of the scattering vector, with positions ki (i = 1, 2 or 3) that scale with the nearest-neighbour distance. Different length scales emerge with complexity of the bonding scheme. A peak at k3 is a generic feature associated with nearest-neighbour contacts, and is therefore present in for all of the materials. A second longer-length scale emerges as a peak at if the bonding scheme assumes a directional character, leading to the formation of tetrahedral motifs in amorphous silicon and patchy colloids, or to Se–Se–Se chain segments in glassy selenium. A third still-longer-length scale appears for AX2 glasses as a first sharp diffraction peak at , where the scaled peak position depends on the character of the local network of A atoms. The geometrical origin of the peaks in and corresponding partial structure factors is considered, and equations are given for predicting the peak positions. The change in system fragility with the emergence of ordering on different length scales is discussed, along with the effect of pressure.

Dynamical processes related to viscous flow in a supercooled arsenic selenide glass-forming liquid: Results from high-temperature 77Se NMR spectroscopy

Dynamical processes in supercooled AsSe9 liquid are studied using 1D and 2D 77Se NMR spectroscopic techniques. The results demonstrate the coexistence of two distinct dynamical processes: one is a slow process related to the chemical exchange between the various Se environments by bond scission/renewal and the other is the fast Se chain segmental motion, which leads to the rapid averaging of the chemical shift anisotropy. The timescales of these two processes become increasingly similar as the glass transition is approached from above. The slow process is found to be closely coupled to viscosity over the entire temperature range of investigation and its activation energy is consistent with the Se-Se/As bond energies. On the other hand, the activation energy of the fast process is significantly higher, which may be indicative of its cooperative nature. This process becomes coupled to viscosity only in the immediate vicinity of the glass transition.

NpSe2 : a Binary Chalcogenide Containing Modulated Selenide Chains and Ambiguous-Valent Metal.

A new binary compound, NpSe2, possesses metal-chalcogen and chalcogen-chalcogen interactions different from those reported for other metal dichalcogenides. Its structure is incommensurately modulated and features linear Se chains and valence-ambiguous Np cations.

The First Naked Bismuth-Chalcogen Metal Carbonyl Clusters: Extraordinary Nucleophilicity of the Bi Atom and Semiconducting Characteristics.

Mixed bismuth-chalcogen-iron clusters [{EFe3(CO)9}Bi]- [E = Te (1a) or Se (1b)] were produced via the reduction of BiCl3 with [EFe3(CO)9]2- under mild conditions. X-ray analysis showed that both clusters 1a and 1b had a square-pyramidal geometry, where the naked Bi and chalcogen both adopted a distorted trigonal-pyramidal configuration with a stereoactive lone pair. Complexes 1a and 1b can be further functionalized by methylation and metalation, which permits the nucleophilicity of the 6s/5s and 6s/4s lone pairs to be compared. In the metalation, the 6s pair of the Bi atom in 1a and 1b had an extraordinary nucleophilicity toward the unsaturated Cr(CO)5 fragment, even in the presence of the more chemically active 5s or 4s pair, whereas in the case of methylation, only the 4s pair of Se could be selectively alkylated. Upon oxidation of 1a and 1b with suitable oxidizing agents, NaBiO3 or K2SeO3, Bi-E bonded tetrahedral complexes [{EFe2(CO)6}Bi]- [E = Te (4a) or Se (4b)] were formed by the elimination of one Fe(CO)3 vertex. X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory (DFT) calculations showed that all of the Bi atoms in these complexes had oxidation states close to +1. Due to the electropositive character of the Bi atom, pronounced induced Bi···E inter- and intramolecular interactions were evident in 1a (1b), 4a (4b), and the metalated 3a (3b), where their linear-like ···Bi···E··· or zigzag-like ···Bi-E··· (E = Te or Se) chain or the Bi···E···E···Bi (E = Te or Se) dimeric chain can further expand into the two-dimensional network via nonclassical C-H···O(carbonyl) interactions, supported by noncovalent interaction index and DFT calculations. These positively charged Bi-induced Bi···E (E = Te or Se) and carbonyl-aided weak interactions can facilitate efficient electron transport within these ternary Bi-E-Fe or quaternary Bi-E-Fe-Cr cluster-based frameworks, resulting in semiconducting behavior with surprising ultranarrow energy gaps of 1.01-1.21 eV.

How different are Te clusters—a first-principles study

Density functional theory-based electronic structure calculations are carried out to obtain the geometries corresponding to the lowest three energy values for Tey (y = 2 − 20) clusters. A comparison of the stability from binding energy curve of these clusters with exchange-correlation energy functional approximated within the local density approximation (LDA), generalized gradient approximation (GGA) and hybrid functional (PBE0) indicates the structures to be most stable within the LDA, and these results are also found to be closer to those obtained from the experiments. A transition from two-dimensional to three-dimensional structures is observed at y = 5. Clusters form arm-chair and crown-like structures for small sizes and ring-like geometries for larger sizes. Partial charge density and eigenvalue spectrum reveal that there is no s-p hybridization and the highest occupied states are mostly π non-bonding orbitals. Clusters with even number of atoms show a charge distribution approximately uniformly localized around each atom similar to the σs anti-bonding orbital in Te2. Comparative study of the structural and electronic properties of small Tey clusters (y = 2 − 8), with corresponding isoelectronic sulphur and selenium clusters, predicts sulphur clusters to be most stable and Te clusters to be least stable. Bond lengths increase while bond angles decrease in going from S → Se → Te but the shapes of the geometric structures are more or less the same. Following the work of Ghosh et al. (J Phys Chem C 112:983–989, 2008) on Te helical structures and Pal et al. (Sci Rep 3:2051-1-7, 2013) on Se helical chains, we have carried out spin-polarized electronic structure calculations for helical chains of Tey (y = 3 − 8). Interestingly, we have found that Te helical chains also reveal a behaviour similar to that predicted for Se chains by Pal et al.

Short and medium range structures of 80GeSe2–20Ga2Se3 chalcogenide glasses

The short and medium range structures of 80GeSe2–20Ga2Se3 (or Ge23.5Ga11.8Se64.7) chalcogenide glasses have been studied by combining ab initio molecular dynamics (AIMD) simulations and experimental neutron diffraction studies. The structure factor and total correlation function were calculated from glass structures generated from AIMD simulations and compared with neutron diffraction experiments showing reasonable agreement. The atomic structures of ternary chalcogenide glasses were analyzed in detail, and it was found that gallium atoms are four-fold coordinated by selenium (Se) and form [GaSe4] tetrahedra. Germanium atoms on average also have four-fold coordination, among which Se is 3.5 with the remaining being Ge–Ge homo-nuclear bonds. Ga and Ge tetrahedra link together mainly through corner-sharing and some edge-sharing of Se. No homo-nuclear bonds were observed among Ga atoms or between Ge and Ga. In addition, Se–Se homo-nuclear bonds and Se chains with various lengths were observed. A small fraction of Se atom triclusters that bond to three cations of Ge and Ga were also observed, confirming earlier proposals from 77Se solid state nuclear magnetic resonance studies. Furthermore, the electronic structures of ternary chalcogenide glasses were studied in terms of atomic charge and electronic density of states in order to gain insights into the chemical bonding and electronic properties, as well as to provide an explanation of the observed atomic structures in these ternary chalcogenide glasses.