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Solvated electrons in alkali metal-ammonia solutions have attracted attention as a prototype electronic conductor and chemical reducing agent for over a century. However, solvated electrons have not been realized in a high-temperature melt or glass of an oxide system to date. We demonstrated the formation of persistent solvated electrons in both a high-temperature melt and its glass by using the thermally stable electride [Ca24Al28O64]4+⋅4e- (C12A7:e-) and controlling the partial pressure of oxygen. The electrical and structural properties of the resulting melt and glass differ from those of the conventional C12A7:02- oxide, exhibiting metallic and hopping conduction, respectively, and a glass transition temperature that is ~160 kelvin lower than that of C12A7:02- glass. Solvated electrons reside in cage structures in C12A7:e- and form a diamagnetic paired state. [ABSTRACT FROM AUTHOR]

Pore-free ⟨110⟩ oriented 12CaO·7Al 2O 3(C12A7) single crystals with sizes up to 7 mm (Phi) × 40 mm are grown by controlling the melt states in a floating zone (Fz) method. Control is achieved by increasing the melt temperature to ∼1495 °C and using a high-density C12A7 polycrystalline feed rod, which reduces oxygen bubbles in the melt almost completely due to a distinct decrease in O 2-solubility with temperature increase. The optimization of the melt temperature, coupled with ⟨110⟩ oriented single crystal as a seed and the decreased growth speed, allows high-quality crystal growth. The grown crystal exhibits a good internal transparency (above 98% in the visible region) and does not contain magnetic impurities such as Ir, which are inevitably incorporated in Czochralski grown crystals. The crystal can be used as a precursor for superconductive C12A7:e −. [ABSTRACT FROM AUTHOR]

We report a metallic state in a nanostructured porous crystal 12CaO·7Al2O3by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping (∼2 × 1021cm-3), which was achieved by a thermal treatment in Ti metal vapor at ∼1100 °C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator−metal transition with a sharp enhancement of the electron drift mobility from ∼0.1 to 4 cm2V-1s-1. The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures. [ABSTRACT FROM AUTHOR]

Thermal field emission (TFE) from a flat surface of 12CaO·7Al2O3 (C12A7) electride was examined at temperatures up to 900 °C and applied external voltages of 0–6 kV in a 10-5 Pa vacuum. TFE started to occur at ∼650 °C and steeply increased at ∼900 °C to reach ∼80 μA (∼1.5 A cm-2) when an extraction field of 105 V cm-1 (an extraction voltage of 6 kV) was applied. The work function estimated from the Richardson–Dushman equation was ∼2.1 eV, which is rather smaller than that of LaB6 (∼2.7 eV). It is experimentally confirmed that the emission with a current of ∼50 μA (from a 80 μm diameter area) was stably sustained for more than 90 h. The efficient and stable emission at relatively low temperature in a moderate vacuum atmosphere strongly suggests that the C12A7 electride has high potential for TFE applications. [ABSTRACT FROM AUTHOR]

We introduce a new class of electrides with nontrivial band topology by coupling materials database searches and first-principles-calculations-based analysis. Cs3O and Ba3N are for the first time identified as a new class of electrides, consisting of one-dimensional (1D) nanorod building blocks. Their crystal structures mimic β-TiCl3 with the position of anions and cations exchanged. Unlike the weakly coupled nanorods of β-TiCl3, Cs3O and Ba3N retain 1D anionic electrons along the hollow interrod sites; additionally, a strong interrod interaction in C3O and Ba3N induces band inversion in a 2D superatomic triangular lattice, resulting in Dirac-node lines. The new class of electrides can serve as a prototype for new electrides with a large cavity space that can be utilized for various applications such as gas storage, ion transport, and metal intercalation. [ABSTRACT FROM AUTHOR]

S-band metals such as alkali and alkaline earth metals do not undergo a superconducting transition (SCT) at ambient pressure, but their high-pressure phases do. By contrast, room-temperature stable electride [Ca24Al28O64] 4+⋅4e- (C12A7:e-) in which anionic electrons in the crystallographic sub-nanometer-size cages have high s-character exhibits SCT at 0.2-0.4 K at ambient pressure. In this paper, we report that crystal and electronic structures of C12A7:e- are close to those of the high-pressure superconducting phase of alkali and alkaline earth metals and the SCT of both materials is induced when electron nature at Fermi energy (EF) switches from s- to sd-hybridized state. [ABSTRACT FROM AUTHOR]

We report herein on Ruddlesden–Popper-type doped Sr n+1Ti nO3 n+1 ( n=2) as a potential candidate for n-type thermoelectric (TE) oxides. The TE properties of 5 at.% La-, Nd-, and Nb-doped Sr3Ti2O7 polycrystalline ceramics were investigated and the origin of Seebeck coefficient was discussed from the viewpoint of the symmetry of TiO6 octahedra. A significant reduction in the lattice thermal conductivity was observed by the enhancement of phonon scattering at SrO/(SrTiO3) n interfaces originating from the inherent superlattice structure, and the maximum dimensionless figure of merit, ZT∼0.15, at a 1000 K value was obtained in 5 at.% La-doped Sr3Ti2O7. [ABSTRACT FROM AUTHOR]

The article discusses on water- and acid-stable self-passivated dihafnium sulfide electride and its persistent electrocatalytic reaction. Topics include information on self-passivated dihafnium sulfide electride that exhibits oxidation resistance in water and acid solutions; use of self-passivation mechanism in reactive conditions for advance development of stable electrides for energy-efficient applications; and need for Ambient-stable electrides to passivate the reactive excess electrons.

We report that the spin-alignment of interstitial anionic electrons (IAEs) in two-dimensional (2D) interlayer spacing can be tuned by chemical pressure that controls the magnetic properties of 2D electrides. It was clarified from the isovalent Sc substitution on the Y site in the 2D Y²C electride that the localization degree of IAEs at the interlayer becomes stronger as the unit cell volume and c-axis lattice parameter were systematically reduced by increasing the Sc contents, thus eventually enhancing superparamagnetic behavior originated from the increase in ferromagnetic particle concentration. It was also found that the spin-aligned localized IAEs dominated the electrical conduction of heavily Sc-substituted Y²C electride. These results indicate that the physcial properties of 2D electrides can be tailored by adjusting the localization of IAEs at interlayer spacing via structural modification that controls the spin instability as found in three-dimensional elemental electrides of pressurized potassium metals. [ABSTRACT FROM AUTHOR]

Demands on high-quality layer structured two-dimensional (2D) thin films such as pnictogen chalcogenides and transition metal dichalcogenides are growing due to the findings of exotic physical properties and potentials for device applications. However, the difficulties in controlling epitaxial growth and the unclear understanding of van der Waals epitaxy (vdWE) for a 2D chalcogenide film on a three-dimensional (3D) substrate have been major obstacles for the further advances of 2D materials. Here, we exploit the spontaneous vdWE of a high-quality 2D chalcogenide (Bi0.5Sb1.5Te3) film by the chalcogen-driven surface reconstruction of a conventional 3D sapphire substrate. It is verified that the in situ formation of a pseudomorphic Te atomic monolayer on the surface of sapphire, which results in a dangling bond-free surface, allows the spontaneous vdWE of 2D chalcogenide film. Since this route uses the natural surface reconstruction of sapphire with chalcogen under vacuum condition, it can be scalable and easily utilized for the developments of various 2D chalcogenide vdWE films through conventional thin-film fabrication technologies. [ABSTRACT FROM AUTHOR]

Cation substitutional doping is an effective approach to modifying the electronic and thermal transports in Bi2Te3-based thermoelectric alloys. Here we present a comprehensive analysis of the electrical and thermal conductivities of polycrystalline Pb-doped p-type bulk Bi0.48Sb1.52Te3. Pb doping significantly increased the electrical conductivity up to ~2700 S/cm at x = 0.02 in Bi0.48-xPbxSb1.52Te3 due to the increase in hole carrier concentration. Even though the total thermal conductivity increased as Pb was added, due to the increased hole carrier concentration, the thermal conductivity was reduced by 14-22% if the contribution of the increased hole carrier concentration was excluded. To further understand the origin of reduction in the thermal conductivity, we first estimated the contribution of bipolar conduction to thermal conductivity from a two-parabolic band model, which is an extension of the single parabolic band model. Thereafter, the contribution of additional point defect scattering caused by Pb substitution (Pb in the cation site) was analyzed using the Debye-Callaway model. We found that Pb doping significantly suppressed both the bipolar thermal conduction and lattice thermal conductivity simultaneously, while the bipolar contribution to the total thermal conductivity reduction increased at high temperatures. At Pb doping of x = 0.02, the bipolar thermal conductivity decreased by ~30% from 0.47 W/mK to 0.33 W/mK at 480 K, which accounts for 70% of the total reduction. [ABSTRACT FROM AUTHOR]

Doping two-dimensional (2D) semiconductors beyond their degenerate levels provides the opportunity to investigate extreme carrier density-driven superconductivity and phase transition in 2D systems. Chemical functionalization and the ionic gating have achieved the high doping density, but their effective ranges have been limited to ~1 nm, which restricts the use of highly doped 2D semiconductors. Here, we report on electron diffusion from the 2D electride [Ca2N]+·e- to MoTe2 over a distance of 100 nm from the contact interface, generating an electron doping density higher than 1.6 × 1014 cm-2 and a lattice symmetry change of MoTe2 as a consequence of the extreme doping. The long-range lattice symmetry change, suggesting a length scale surpassing the depletion width of conventional metal-semiconductor junctions, was a consequence of the low work function (2.6 eV) with highly mobile anionic electron layers of [Ca2N]+·e-. The combination of 2D electrides and layered materials yields a novel material design in terms of doping and lattice engineering. [ABSTRACT FROM AUTHOR]

Halogenated organic compounds are important anthropogenic chemicals widely used in chemical industry, biology, and pharmacology; however, the persistence and inertness of organic halides cause human health problems and considerable environmental pollution. Thus, the elimination or replacement of halogen atoms with organic halides has been considered a central task in synthetic chemistry. In dehalogenation reactions, the consecutive single-electron transfer from reducing agents generates the radical and corresponding carbanion and thus removes the halogen atom as the leaving group. Herein, we report a new strategy for an efficient chemoselective hydrodehalogenation through the formation of stable carbanion intermediates, which are simply achieved by using highly mobile two-dimensional electrons of inorganic electride [Ca2N]+ ⋅ e- with effective electron transfer ability. The consecutive single-electron transfer from inorganic electride [Ca2N]+ ⋅ e- stabilized free carbanions, which is a key step in achieving the selective reaction. Furthermore, a determinant more important than leaving group ability is the stability control of free carbanions according to the s character determined by the backbone structure. We anticipate that this approach may provide new insight into selective chemical formation, including hydrodehalogenation. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) electrides, emerging as a new type of layered material whose electrons are confined in interlayer spaces instead of at atomic proximities, are receiving interest for their high performance in various (opto)electronics and catalytic applications. Experimentally, however, 2D electrides have been only found in a couple of layered nitrides and carbides. Here, we report new thermodynamically stable alkaline-earth based 2D electrides by using a first-principles global structure optimization method, phonon spectrum analysis, and molecular dynamics simulation. The method was applied to binary compounds consisting of alkaline-earth elements as cations and group VA, VIA, or VIIA nonmetal elements as anions. We revealed that the stability of a layered 2D electride structure is closely related to the cation/anion size ratio; stable 2D electrides possess a sufficiently large cation/anion size ratio to minimize electrostatic energy among cations, anions, and anionic electrons. Our work demonstrates a new avenue to the discovery of thermodynamically stable 2D electrides beyond experimental material databases and provides new insight into the principles of electride design. [ABSTRACT FROM AUTHOR]

Angle-resolved photoemission spectroscopy (ARPES) study of a layered electride Ca2N was carried out to reveal its quasi-two-dimensional electronic structure. The band dispersions and the Fermi-surface map are consistent with the density functional theory results except for a chemical potential shift that may originate from the high reactivity of surface excess electrons. Thus, the existence of anionic excess electrons in the interlayer region of Ca2N is strongly supported by ARPES. [ABSTRACT FROM AUTHOR]

Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T') molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 106. In situ scanning transmission electron microscopy results combined with theoretical calculations reveal that the Te vacancy triggers the local phase transition in MoTe2, achieving a true 2D device with an ohmic contact. [ABSTRACT FROM AUTHOR]

The successful mechanical exfoliationand chemical synthesis ofgraphene has attracted considerable attention for the synthesis ofother two-dimensional materials on graphene template. Chalcogenidematerials such as Sb2Te3are of interest dueto the rhombohedral lattice structure with two-dimensional hexagonallyclosed-packed atomic layers along the c-axis. Herewe synthesized c-axis-oriented Sb2Te3nanoplates (NPs) on graphene substrates by the microwave-assistedsolvothermal method. The microwave irradiation resulted in a highertemperature of graphene, compared with the synthesis solution, whichwas revealed by the single-mode microwave experiments and an analyticalmodel based on energy balance and convective heat transfer. Besides,the lattice mismatch between c-axis-oriented Sb2Te3and bridge sites of graphene was only 4%, whichis also favorable for the graphene-templated Sb2Te3synthesis. c-Axis-oriented single-crystallineSb2Te3NPs as large as 7 μm could be successfullysynthesized on graphene with negligible damage of the graphene template.Larger surface coverage could be obtained by merging Sb2Te3NPs. The merged Sb2Te3NPs werepolycrystalline with rotated grain boundaries. This work providesa facile, rapid, and low-cost synthesis route of c-axis-oriented Sb2Te3NPs on graphene templates,which may be extended for the synthesis of various two-dimensionalmaterials with hexagonally closed-packed atomic layers along the c-axis. [ABSTRACT FROM AUTHOR]

The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi0.5Sb1.5Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices. [ABSTRACT FROM AUTHOR]

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of Zn-, In-, and I-doped Cu1.7Bi4.7Se8 pavonite homologues were investigated in the temperature range from 300 to 560 K. On the basis of the comprehensive structural analysis using Rietveld refinement of synchrotron radiation diffraction for Cux+yBi5-ySe8 compounds with the inherently disordered crystallographic sites, we demonstrate a doping strategy that provides a simultaneous control for enhanced electronic transport properties by the optimization of carrier concentration and exceptionally low lattice thermal conductivity by the formation of point defects. Substituted Zn or In ions on Cu site was found to be an effective phonon scattering center as well as an electron donor, while doping on Bi site showed a moderate effect for phonon scattering. In addition, we achieved largely enhanced power factor in small amount of In doping on Cu site by increased electrical conductivity and moderately decreased Seebeck coefficient. Coupled with a low lattice thermal conductivity originated from intensified point defect phonon scattering by substituted In ions with host Cu ions, a thermoelectric figure of merit ZT of 0.24 at 560 K for Cu1.6915In0.0085Bi4.7Se8 was achieved, yielding 30% enhancement compared with that of a pristine Cu1.7Bi4.7Se8 at the same temperature. [ABSTRACT FROM AUTHOR]

The scalable pinacol coupling reaction is realized utilizing the inorganic electride [Ca2N]+e-- as an electron donor in organic solvents. The bond cleavages of the [Ca2N]+ layers by methanol play a vital role in transferring anionic electrons to electrophilic aldehydes, accompanying the formation of Ca(OMe)2 and ammonia. [ABSTRACT FROM AUTHOR]

We herein report the electronic and thermal transport properties of p-type Bi0.5Sb1.5Te3 polycrystalline bulks with dense pore structure. Dense pore structure was fabricated by vaporization of residual Te during the pressureless annealing of spark plasma sintered bulks of Te coated Bi0.5Sb1.5Te3 powders. The lattice thermal conductivity was effectively reduced to the value of 0.35Wm-1 K-1 at 300K mainly due to the phonon scattering by pores, while the power factor was not significantly affected. An enhanced ZT of 1.24 at 300K was obtained in spark plasma sintered and annealed bulks of 3wt.% Te coated Bi0.5Sb1.5Te3 by these synergetic effects. [ABSTRACT FROM AUTHOR]

Monoclinic Cux+yBi5-ySe8 structure has multiple disorders, such as randomly distributed substitutional and interstitial disorders by Cu as well as asymmetrical disorders by Se. Herein, we report the correlation of electronic and thermal properties with the structural complexities of Cux+yBi5-ySe8. It is found that the interstitial Cu site plays an important role not only to increase the electrical conductivity due to the generation of electron carriers but also to reduce the thermal conductivity mainly due to the phonon scattering by mass fluctuation. With impurity doping at the interstitial Cu site, an extremely low lattice thermal conductivity of 0.32W·m-1 ·K-1 was achieved at 560 K. These synergetic effects result in the enhanced dimensionless figure of merit (ZT). [ABSTRACT FROM AUTHOR]

We performed the neutron powder diffraction (NPD) and synchrotron x-ray diffraction measurements on CeFeAsO1-x(D,H)x, (x = 0.0 -- 0.48) as a representative of 1111 -type family of iron-based superconductors LnFeAsO1-xHx(Ln = lanthanoid). Deuterated andhydrogenatedsamples (CeFeAsOi-xDx, andCeFeAsO1-xHx) were synthesized by the solid-state reaction of a metal oxide, arsenides, and a hydride and a deuteride source under an applied pressure of 2 GPa. No distinct differences were found between the structural and superconducting properties of the hydride and deuteride samples. Rietveld analyses of the NPD patterns demonstrated that deuterium exclusively substitutes on the oxygen sites in the 111 1-type structures according to the nominal composition. Bulk superconductivity was observed over a wide x region (0.1 < x < 0.4) and the superconducting dome had a rather Hat shape with a maximum Tc = 47 K at around x = 0.25. It was concluded from density functional theory calculations and comparison with the superconducting dome of the fluorine-substituted system that the charge state of the hydrogen substituting the oxygen sites was --1. The relationship between the lattice parameter a and Tc in our samples prepared from metal hydrides is almost the same as that reported previously for samples prepared from cerium hydroxide. These results strongly suggest that H- ions exclusively occupy the oxygen sites in both samples, regardless of the hydrogen species in the starting material. [ABSTRACT FROM AUTHOR]

Electrical properties of Br-doped SnSe2 van der Waals (vdW) materials are investigated by synthesizing polycrystalline SnSe2−xBrx via a solid-state reaction route. From the x-ray diffraction and Raman spectra results, it can be confirmed that Br impurity substitutes well on a Se-site by minimizing the lattice deformation as well as the red-shift of A1g vibrational mode corresponding to the Sn–Se bond. Electrical characterization reveals that Br dopant is an efficient electron donor for vdW SnSe2 system as it easily encourages the electron carrier concentration from ~1017 to ~1020 cm−3, thus resulting in the semiconductor-metal transition behavior. [ABSTRACT FROM AUTHOR]

Synthesis of monolayer transition metal dichalcogenides (TMDs) via chemical vapor deposition relies on several factors such as precursor, promoter, substrate, and surface treatment of substrate. Among them, the use of promoter is crucial for obtaining uniform and large-area monolayer TMDs. Although promoters have been speculated to enhance adhesion of precursors to the substrate, their precise role in the growth mechanism has rarely been discussed. Here, we report the role of alkali metal promoter in growing monolayer TMDs. The growth occurred via the formation of sodium metal oxides which prevent the evaporation of metal precursor. Furthermore, the silicon oxide substrate helped to decrease the Gibbs free energy by forming sodium silicon oxide compounds. The resulting sodium metal oxide was anchored within such concavities created by corrosion of silicon oxide. Consequently, the wettability of the precursors to silicon oxide was improved, leading to enhance lateral growth of monolayer TMDs. [ABSTRACT FROM AUTHOR]

The electronic band structure of crystals is generally influenced by the periodic arrangement of their constituent atoms. Specifically, the emerging two-dimensional (2D) layered structures have shown different band structures with respect to their stacking configurations. Here, based on first-principles density-functional theory calculations, we demonstrate that the band structure of the recently synthesized 2D Ca2N electride changes little for the stacking sequence as well as the lateral interlayer shift. This intriguing invariance of band structure with respect to geometrical variations can be attributed to a complete screening of [Ca2N]+ cationic layers by anionic excess electrons delocalized between the cationic layers. The resulting weak interactions between 2D dressed cationic layers give rise to not only a shallow potential barrier for bilayer sliding but also an electron-doping-facilitated shear exfoliation. Our findings open a route for exploration of the peculiar geometry-insensitive electronic properties in 2D electride materials, which will be useful for future thermally stable electronic applications. [ABSTRACT FROM AUTHOR]