Breaking New Ground: MBene Route toward Selective Vinyl Double Bond Hydrogenation in Nitroarenes.

Doping, or incremental substitution of one element for another, is an effective way to tailor a compound's structure as well as its physical and chemical properties. Herein, we replaced up to 30% of Ni with Co in members of the family of layered LiNiB compounds, stabilizing the high-temperature polymorph of LiNiB while the room-temperature polymorph does not form. By studying this layered boride with in situ high-temperature powder diffraction, we obtained a distorted variant of LiNi0.7Co0.3B featuring a perfect interlayer placement of [Ni0.7Co0.3B] layers on top of each other─a structural motif not seen before in other borides. Because of the Co doping, LiNi0.7Co0.3B can undergo a nearly complete topochemical Li deintercalation under ambient conditions, resulting in a metastable boride with the formula Li0.04Ni0.7Co0.3B. Heating of Li0.04Ni0.7Co0.3B in anaerobic conditions led to yet another metastable boride, Li0.01Ni0.7Co0.3B, with a CoB-type crystal structure that cannot be obtained by simple annealing of Ni, Co, and B. No significant alterations of magnetic properties were detected upon Co-doping in the temperature-independent paramagnet LiNi0.7Co0.3B or its Li-deintercalated counterparts. Finally, Li0.01Ni0.7Co0.3B stands out as an exceptional catalyst for the selective hydrogenation of the vinyl C═C bond in 3-nitrostyrene, even in the presence of other competing functional groups. This research showcases an innovative approach to heterogeneous catalyst design by meticulously synthesizing metastable compounds.

Path Less Traveled: A Contemporary Twist on Synthesis and Traditional Structure Solution of Metastable LiNi12B8.

Achieving kinetic control to synthesize metastable compounds is a challenging task, especially in solid-state reactions where the diffusion is slow. Another challenge is the unambiguous crystal structure determination for metastable compounds when high-quality single crystals suitable for single-crystal X-ray diffraction are inaccessible. In this work, we report an unconventional means of synthesis and an effective strategy to solve the crystal structure of an unprecedented metastable compound LiNi12B8. This compound can only be produced upon heating a metastable layered boride, HT-Li0.4NiB (HT: high temperature), in a sealed niobium container. A conventional heating and annealing of elements do not yield the title compound, which is consistent with the metastable nature of LiNi12B8. The process to crystallize this compound is sensitive to the annealing temperature and dwelling time, a testament to the complex kinetics involved in the formation of the product. The unavailability of crystals suitable for single-crystal X-ray diffraction experiments prompted solving the crystal structure from high-resolution synchrotron powder X-ray diffraction data. This compound crystallizes in a new structure type with space group I4/mmm (a = 10.55673(9) Å, c = 10.00982(8) Å, V = 1115.54(3) Å3, Z = 6). The resulting complex crystal structure of LiNi12B8 is confirmed by scanning transmission electron microscopy and solid-state 11B and 7Li NMR spectroscopy analyses. The extended Ni framework with Li/Ni disorder in its crystal structure resulted in the spin-glass or cluster glass type magnetic ordering below 24 K. This report illustrates a "contemporary twist" to traditional methodologies toward synthesizing a metastable compound and provides a recipe for solving structures by combining the complementary characterization techniques in the cases where the traditionally used single-crystal X-ray diffraction method is nonapplicable.

Deep Eutectic Solvent Synthesis of Perovskite Electrocatalysts for Water Oxidation.

Oxide perovskites have attracted great interest as materials for energy conversion due to their stability and structural tunability. La-based perovskites of 3d-transition metals have demonstrated excellent activities as electrocatalysts in water oxidation. Herein, we report the synthesis route to La-based perovskites using an environmentally friendly deep eutectic solvent (DES) consisting of choline chloride and malonic acid. The DES route affords phase-pure crystalline materials on a gram scale and results in perovskites with high electrocatalytic activity for oxygen evolution reaction. A convenient, fast, and scalable synthesis proceeds via assisted metathesis at a lower temperature as compared to traditional solid-state methods. Among LaCoO3, LaMn0.5Ni0.5O3, and LaMnO3 perovskites prepared via the DES route, LaCoO3 was established to be the best-performing electrocatalyst for water oxidation in alkaline medium at 0.25 mg cm-2 mass loading. LaCoO3 exhibits current densities of 10, 50, and 100 mA cm-2 at respective overpotentials of approximately 390, 430, and 470 mV, respectively, and features a Tafel slope of 55.8 mV dec-1. The high activity of LaCoO3 as compared to the other prepared perovskites is attributed to the high concentration of oxygen vacancies in the LaCoO3 lattice, as observed by high-resolution transmission electron microscopy. An intrinsically high concentration of O vacancies in the LaCoO3 synthesized via the DES route is ascribed to the reducing atmosphere attained upon thermal decomposition of the DES components. These findings will contribute to the preparation of highly active perovskites for various energy applications.

Microwave-Assisted Solution Synthesis of Metastable Intergrowth of AgInS2 Polymorphs.

The intergrowth of stable and metastable AgInS2 polymorphs was synthesized using a microwave-assisted synthesis. The samples were synthesized in water and in a deep eutectic solvent (DES) consisting of choline chloride and thiourea. An increase in the metal precursor concentration improved the crystallinity of the synthesized samples and affected the particle size. AgInS2 cannot be synthesized from crystalline binary Ag2S or In2S3 via this route. The solution synthesis reported here results in the intergrowth of the thermodynamically stable polymorph (space group I4¯2d, chalcopyrite structure) and the high-temperature polymorph (space group Pna21, wurtzite-like structure) that is metastable at room temperature. A scanning transmission microscopy (STEM) study revealed the intergrowth of tetragonal and orthorhombic polymorphs in a single particle and unambiguously established that the long-thought hexagonal wurtzite polymorph has pseudo-hexagonal symmetry and is best described with the orthorhombic unit cell. The solution-synthesized AgInS2 polymorphs intergrowth has slightly lower bandgap values in the range of 1.73 eV-1.91 eV compared to the previously reported values for tetragonal I4¯2d (1.86 eV) and orthorhombic Pna21 (1.98 eV) polymorphs.

The Deep Eutectic Solvent Precipitation Synthesis of Metastable Zn4V2O9.

A precipitation method involving a deep eutectic solvent (DES)─a mixture of hydrogen bond donor and acceptor─is used to synthesize a ternary metal oxide. Without toxic reagents, precipitates consisting of Zn3(OH)2V2O7·nH2O and Zn5(OH)6(CO3)2 are obtained by simply introducing deionized H2O to the DES solution containing dissolved ZnO and V2O5. Manipulation of the synthetic conditions demonstrates high tunability in the size/morphology of the two-dimensional nanosheets precipitated during the dynamic equilibrium process. According to differential scanning calorimetry and high-temperature powder X-ray diffraction, Zn3V2O8 and ZnO obtained by the annealing of the precipitate are intermediates in the reaction pathway toward metastable Zn4V2O9. Intimate mixing of the metal precursors achieved by the precipitation method allows access to the metastable zinc-rich vanadate with unusually rapid heat treatment. The UV-vis and surface photovoltage spectra reveal the presence of sub-band gap states, stemming from the reduced vanadium (V4+) center. Photoelectrochemical measurements confirm weak photoanodic currents for water and methanol oxidation. For the first time, this work shows the synthesis of a metastable oxide with the DES-precipitation route and provides insight into the structure-property relationship of the zinc-rich vanadate.

A Low-Temperature Structural Transition in Canfieldite, Ag8SnS6, Single Crystals.

Canfieldite, Ag8SnS6, is a semiconducting mineral notable for its high ionic conductivity, photosensitivity, and low thermal conductivity. We report the solution growth of large single crystals of Ag8SnS6 of mass up to 1 g from a ternary Ag-Sn-S melt. On cooling from high temperature, Ag8SnS6 undergoes a known cubic (F4̅3m) to orthorhombic (Pna21) phase transition at ≈460 K. By studying the magnetization and thermal expansion between 5-300 K, we discover a second structural transition at ≈120 K. Single crystal X-ray diffraction reveals the low-temperature phase adopts a different orthorhombic structure with space group Pmn21 (a = 7.662 9(5) Å, b = 7.539 6(5) Å, c = 10.630 0(5) Å, Z = 2 at 90 K) that is isostructural to the room-temperature forms of the related Se-based compounds Ag8SnSe6 and Ag8GeSe6. The 120 K transition is first-order and has a large thermal hysteresis. On the basis of the magnetization and thermal expansion data, the room-temperature polymorph can be kinetically arrested into a metastable state by rapidly cooling to temperatures below 40 K. We last compare the room- and low-temperature forms of Ag8SnS6 with its argyrodite analogues, Ag8TQ6 (T = Si, Ge, Sn; Q = S, Se), and identify a trend relating the preferred structures to the unit cell volume, suggesting smaller phase volume favors the Pna21 arrangement. We support this picture by showing that the transition to the Pmn21 phase is avoided in Ge alloyed Ag8Sn1-xGexS6 samples as well as in pure Ag8GeS6.

How to Look for Compounds: Predictive Screening and in†situ Studies in Na-Zn-Bi System.

Here, the combination of theoretical computations followed by rapid experimental screening and in situ diffraction studies is demonstrated as a powerful strategy for novel compounds discovery. When applied for the previously "empty" Na-Zn-Bi system, such an approach led to four novel phases. The compositional space of this system was rapidly screened via the hydride route method and the theoretically predicted NaZnBi (PbClF type, P4/nmm) and Na11 Zn2 Bi5 (Na11 Cd2 Sb5 type, P 1 ‾ ) phases were successfully synthesized, while other computationally generated compounds on the list were rejected. In addition, single crystal X-ray diffraction studies of NaZnBi indicate minor deviations from the stoichiometric 1 : 1 : 1 molar ratio. As a result, two isostructural (PbClF type, P4/nmm) Zn-deficient phases with similar compositions, but distinctly different unit cell parameters were discovered. The vacancies on Zn sites and unit cell expansion were rationalized from bonding analysis using electronic structure calculations on stoichiometric "NaZnBi". In-situ synchrotron powder X-ray diffraction studies shed light on complex equilibria in the Na-Zn-Bi system at elevated temperatures. In particular, the high-temperature polymorph HT-Na3 Bi (BiF3 type, Fm 3 ‾ m) was obtained as a product of Na11 Zn2 Bi5 decomposition above 611 K. HT-Na3 Bi cannot be stabilized at room temperature by quenching, and this type of structure was earlier observed in the high-pressure polymorph HP-Na3 Bi above 0.5 GPa. The aforementioned approach of predictive synthesis can be extended to other multinary systems.

Ternary Zinc Antimonides Unlocked Using Hydride Synthesis.

Three new sodium zinc antimonides Na11Zn2Sb5, Na4Zn9Sb9, and NaZn3Sb3 were synthesized utilizing sodium hydride NaH as a reactive sodium source. In comparison to the synthesis using sodium metal, salt-like NaH can be ball-milled, leading to the easy and uniform mixing of precursors in the desired stoichiometric ratios. Such comprehensive compositional control enables a fast screening of the Na-Zn-Sb system and identification of new compounds, followed by their preparation in bulk with high purity. Na11Zn2Sb5 crystallizes in the triclinic P1 space group (No. 2, Z = 2, a = 8.8739(6) Å, b = 10.6407(7) Å, c = 11.4282(8) Å, α = 103.453(2)°, ß = 96.997(2)°, γ = 107.517(2)°) and features polyanionic [Zn2Sb5]11- clusters with unusual 3-coordinated Zn atoms. Both Na4Zn9Sb9 (Z = 4, a = 28.4794(4) Å, b = 4.47189(5) Å, c = 17.2704(2) Å, ß = 98.3363(6)°) and NaZn3Sb3 (Z = 8, a = 32.1790(1) Å, b = 4.51549(1) Å, c = 9.64569(2) Å, ß = 98.4618(1)°) crystallize in the monoclinic C2/m space group (No. 12) and have complex new structure types. For both compounds, their frameworks are built from ZnSb4 distorted tetrahedra, which are linked via edge-, vertex-sharing, or both, while Na cations fill in the framework channels. Due to the complex structures, Na4Zn9Sb9 and NaZn3Sb3 compounds exhibit low thermal conductivities (0.97-1.26 W·m-1 K-1) at room temperature, positive Seebeck coefficients (19-32 µV/K) suggestive of holes as charge carriers, and semimetallic electrical resistivities (∼1.0-2.3 × 10-4 Ω·m). Na4Zn9Sb9 and NaZn3Sb3 decompose into the equiatomic NaZnSb above ∼800 K, as determined by in situ synchrotron powder X-ray diffraction. The discovery of multiple ternary compounds highlights the importance of judicious choice of the synthetic method.

Topochemical Deintercalation of Li from Layered LiNiB: toward 2D MBene.

The pursuit of two-dimensional (2D) borides, MBenes, has proven to be challenging, not the least because of the lack of a suitable precursor prone to the deintercalation. Here, we studied room-temperature topochemical deintercalation of lithium from the layered polymorphs of the LiNiB compound with a considerable amount of Li stored in between [NiB] layers (33 at. % Li). Deintercalation of Li leads to novel metastable borides (Li∼0.5NiB) with unique crystal structures. Partial removal of Li is accomplished by exposing the parent phases to air, water, or dilute HCl under ambient conditions. Scanning transmission electron microscopy and solid-state 7Li and 11B NMR spectroscopy, combined with X-ray pair distribution function (PDF) analysis and DFT calculations, were utilized to elucidate the novel structures of Li∼0.5NiB and the mechanism of Li-deintercalation. We have shown that the deintercalation of Li proceeds via a "zip-lock" mechanism, leading to the condensation of single [NiB] layers into double or triple layers bound via covalent bonds, resulting in structural fragments with Li[NiB]2 and Li[NiB]3 compositions. The crystal structure of Li∼0.5NiB is best described as an intergrowth of the ordered single [NiB], double [NiB]2, or triple [NiB]3 layers alternating with single Li layers; this explains its structural complexity. The formation of double or triple [NiB] layers induces a change in the magnetic behavior from temperature-independent paramagnets in the parent LiNiB compounds to the spin-glassiness in the deintercalated Li∼0.5NiB counterparts. LiNiB compounds showcase the potential to access a plethora of unique materials, including 2D MBenes (NiB).

Clathrate XI K58 Zn122 Sb207 : A New Branch on the Clathrate Family Tree.

The compositional screening of K-Zn-Sb ternary system aided by machine learning, rapid exploratory synthesis using KH salt-like precursor and in situ powder X-ray diffraction yielded a novel clathrate type XI K58 Zn122 Sb207 . This clathrate consists of a 3D Zn-Sb framework hosting K+ ions inside polyhedral cages, some of which are reminiscent of known clathrate types while others are unique to this structure type. The complex non-centrosymmetric structure in the tetragonal space group I 4 ‾ 2 m was solved by means of single crystal X-ray diffraction as a 6-component twin due to pseudocubic symmetry and further confirmed by high-resolution synchrotron powder X-ray diffraction and state-of-the-art scanning transmission electron microscopy. The electron-precise composition of this clathrate yields narrow-gap p-type semiconductor with extraordinarily low thermal conductivity due to displacement or "rattling" of K cations inside oversized cages and as well as to twinning, stacking faults and antiphase boundary defects.

Computationally Driven Discovery of a Family of Layered LiNiB Polymorphs.

Two novel lithium nickel boride polymorphs, RT-LiNiB and HT-LiNiB, with layered crystal structures are reported. This family of compounds was theoretically predicted by using the adaptive genetic algorithm (AGA) and subsequently synthesized by a hydride route with LiH as the lithium source. Unique among the known ternary transition-metal borides, the LiNiB structures feature Li layers alternating with nearly planar [NiB] layers composed of Ni hexagonal rings with a B-B pair at the center. A comprehensive study using a combination of single crystal/synchrotron powder X-ray diffraction, solid-state 7 Li and 11 B NMR spectroscopy, scanning transmission electron microscopy, quantum-chemical calculations, and magnetism has shed light on the intrinsic features of these polymorphic compounds. The unique layered structures of LiNiB compounds make them ultimate precursors for exfoliation studies, thus paving a way toward two-dimensional transition-metal borides, MBenes.

A Hydride Route to Ternary Alkali Metal Borides: A Case Study of Lithium Nickel Borides.

Ternary lithium nickel borides LiNi3 B1.8 and Li2.8 Ni16 B8 have been synthesized by using reactive LiH as a precursor. This synthetic route allows better mixing of the precursor powders, thus facilitating rapid preparation of the alkali-metal-containing ternary borides. This method is suitable for "fast screening" of multicomponent systems comprised of elements with drastically different reactivities. The crystal structures of the compounds LiNi3 B1.8 and Li2.8 Ni16 B8 have been re-investigated by a combination of single-crystal X-ray/synchrotron powder diffraction, solid-state 7 Li and 11 B NMR spectroscopies, and scanning transmission electron microscopy. This has allowed the determination of fine structural details, including the split position of Ni sites and the ordering of B vacancies. Field-dependent and temperature-dependent magnetization measurements are consistent with spin-glass behavior for both samples.

Thermal Stability and Thermoelectric Properties of NaZnSb.

A layered Zintl antimonide NaZnSb (PbClF or Cu2Sb structure type; P4/nmm) was synthesized using the reactive sodium hydride NaH precursor. This method provides comprehensive compositional control and facilitates the fast preparation of high-purity samples in large quantities. NaZnSb is highly reactive to humidity/air and hydrolyzes to NaOH, ZnO, and Sb in aerobic conditions. On the other hand, NaZnSb is thermally stable up to 873 K in vacuum, as no structural changes were observed from high-temperature synchrotron powder X-ray diffraction data in the 300⁻873 K temperature range. The unit cell expansion upon heating is isotropic; however, interatomic distance elongation is not isotropic, consistent with the layered structure. Low- and high-temperature thermoelectric properties were measured on pellets densified by spark plasma sintering. The resistivity of NaZnSb ranges from 11 mΩ∙cm to 31 mΩ∙cm within the 2⁻676 K range, consistent with heavily doped semiconductor behavior, with a narrow band gap of 0.23 eV. NaZnSb has a large positive Seebeck coefficient (244 µV∙K-1 at 476 K), leading to the maximum of zT of 0.23 at 675 K. The measured thermoelectric properties are in good agreement with those predicted by theoretical calculations.

Switching on a Spin Glass: Flux Growth, Structure, and Magnetism of La11Mn13-x-yNixAlySn4-δ Intermetallics.

Reactions of tin and manganese in a lanthanum/nickel eutectic melt in alumina crucibles produce La11Mn13-x-yNixAlySn4-δ (0 ≤ x ≤ 3.6; 2.5 ≤ y ≤ 4.9; 0.6 ≤ δ ≤ 1.1) phases with the stoichiometry dependent on the reactant ratio. These compounds crystallize in a new tetragonal structure type in space group P4/mbm, with a = 8.4197(1) Å, c = 19.2414(3) Å, and Z = 2 for La11Mn8.2Ni0.8Al4Sn3.3. The structure can be viewed as an intergrowth between La6Co11Ga3-type layers and Cr5B3-type La/Sn slabs. This system represents a unique playground to study the itinerant magnetism of diluted icosahedral Mn layers. The dilution of manganese sites in the Mn/Ni/Al layer with nonmagnetic elements has a significant effect on magnetic properties, with low Mn content analogues being paramagnetic and higher Mn content analogues such as La11Mn10Al3Sn3.4 exhibiting spin-glass behavior with a freezing transition at 20 K. The lack of long-range magnetic ordering is confirmed by heat capacity and resistivity measurements.

Breaking the Tetra-Coordinated Framework Rule: New Clathrate Ba8 M24 P28+δ (M=Cu/Zn).

A new clathrate type has been discovered in the Ba/Cu/Zn/P system. The crystal structure of the Ba8 M24 P28+δ (M=Cu/Zn) clathrate is composed of the pentagonal dodecahedra common to clathrates along with a unique 22-vertex polyhedron with two hexagonal faces capped by additional partially occupied phosphorus sites. This is the first example of a clathrate compound where the framework atoms are not in tetrahedral or trigonal-pyramidal coordination. In Ba8 M24 P28+δ a majority of the framework atoms are five- and six-coordinated, a feature more common to electron-rich intermetallics. The crystal structure of this new clathrate was determined by a combination of X-ray and neutron diffraction and was confirmed with solid-state 31 P NMR spectroscopy. Based on chemical bonding analysis, the driving force for the formation of this new clathrate is the excess of electrons generated by a high concentration of Zn atoms in the framework. The rattling of guest atoms in the large cages results in a very low thermal conductivity, a unique feature of the clathrate family of compounds.

Effect of Isovalent Substitution on the Structure and Properties of the Zintl Phase Solid Solution Eu7Cd4Sb8-xAsx (2 ≤ x ≤ 5).

A novel Zintl phase structure type, Eu7Cd4Sb8-xAsx (x = 2, 3, 4, and 5), with the general formula Eu7Cd4Pn8 (Pn = mixed occupancy Sb and As), was synthesized by molten tin flux reaction. Its structure was determined using single-crystal X-ray diffraction methods. This structure type is only preserved for 2 ≤ x ≤ 5 under our experimental conditions, and efforts to synthesize samples with x < 2 or x > 5 resulted in other structure types. The mixed occupancy Sb and As can be thought of as a pseudoatom whose ideal size, in this range of Sb/As ratios, fits the structure. The title phase crystallizes in the I-centered monoclinic space group I2/m (No. 12, Z = 4) with unit cell parameters ranging as follows: a = 19.7116(17)-19.4546(13) Å, b = 4.6751(4)-4.6149(3) Å, c = 24.157(2)-23.871(15) Å, and ß = 95.8798(1)-96.016(5)°, depending on the Sb/As ratio. The structure can be described as parallel double pentagonal tubes resulting from Cd-Pn and Pn-Pn bonding. These double pentagons are formed through corner sharing of the Cd-centered CdPn4 tetrahedra and a Pn-Pn interaction from two adjacent CdPn4 tetrahedra. This structure type is closely related to the Sr11Cd6Sb12 structure type as both share the same bonding features of Pn-Pn bonding and double pentagonal tubes. Electron microprobe analysis confirms the composition of these new Zintl solid solution phases. The As exhibits preferential substitution on specific sites, and site specificity trends are supported by lowest energy models from theoretical calculations. Theoretical calculations also predict that Sb-rich compounds should be metallic or semimetallic and that they should become more insulating as As content increases. Members of the solid-solution order ferromagnetically between 5 and 6 K and exhibit relatively low electrical resistivity between 50 and 300 K, ranging from ∼0.57 to ∼26 mΩ·cm, increasing with increasing As content.

Facile synthesis of Ba(1-x)K(x)Fe2As2 superconductors via hydride route.

We have developed a fast, easy, and scalable synthesis method for Ba(1-x)K(x)Fe2As2 (0 ≤ x ≤ 1) superconductors using hydrides BaH2 and KH as a source of barium and potassium metals. Synthesis from hydrides provides better mixing and easier handling of the starting materials, consequently leading to faster reactions and/or lower synthesis temperatures. The reducing atmosphere provided by the evolved hydrogen facilitates preparation of oxygen-free powders. By a combination of methods we have shown that Ba(1-x)K(x)Fe2As2 obtained via hydride route has the same characteristics as when it is prepared by traditional solid-state synthesis. Refinement from synchrotron powder X-ray diffraction data confirms a linear dependence of unit cell parameters upon K content as well as the tetragonal to orthorhombic transition at low temperatures for compositions with x < 0.2. Magnetic measurements revealed dome-like dependence of superconducting transition temperature Tc upon K content with a maximum of 38 K for x close to 0.4. Electron diffraction and high-resolution high-angle annular dark-field scanning transmission electron microscopy indicates an absence of Ba/K ordering, while local inhomogeneity in the Ba/K distribution takes place at a scale of several angstroms along [110] crystallographic direction.

Ca2LiC3H: a new complex carbide hydride phase grown in metal flux.

The reaction of carbon and CaH2 in a calcium/lithium flux mixture produces crystals of the new compound Ca2LiC3H. This phase forms with a new structure type in tetragonal space group P4/mbm (a = 6.8236(1) Å, c = 3.7518(1) Å, Z = 2, R1 = 0.0151). This is a stuffed variant of the Cs2(NH2)N3 structure, containing hydride anions in octahedral sites; the structure determination by single-crystal X-ray diffraction surprisingly allowed the hydrogen to be detected. The Ca2LiC3H structure also features the rarely seen C3(4-) carbide anion; the protolysis reaction of this compound with ammonium chloride produces C3H4. The electronic properties of Ca2LiC3H were studied by quantum-chemical calculations including band structure and electron localization function (ELF) analysis; the phase is a charge-balanced semiconductor with a calculated band gap of 0.48 eV. This is in agreement with (7)Li, (13)C, and (1)H MAS NMR data, which show resonances in the ionic region instead of the Knight shifted region. ELF analysis of the theoretical nonhydrided Ca2LiC3 structure confirms the ability of these calculations to properly locate hydrides and supports the structural model based on X-ray diffraction data.

Bulk and surface structure and high-temperature thermoelectric properties of inverse clathrate-III in the Si-P-Te system.

The creation of thermoelectric materials for waste heat recovery and direct solar energy conversion is a challenge that forces the development of compounds that combine appreciable thermoelectric figure-of-merit with high thermal and chemical stability. Here we propose a new candidate for high-temperature thermoelectric materials, the type-III Si(172-x)P(x)Te(y) cationic clathrate, in which the framework is composed of partially ordered silicon and phosphorus atoms, whereas tellurium atoms occupy guest positions. We show that the utmost stability of this clathrate (up to 1500 K) in air is ensured by the formation of a nanosized layer of phosphorus-doped silica on the surface, which prevents further oxidation and degradation. As-cast (non-optimized) Si-P-Te clathrates display rather high values of the thermoelectric figure-of-merit (ZT=0.24-0.36) in the temperature range of 700-1100 K. These ZT values are comparable to the best values achieved for the properly doped transition-metal-oxide materials. The methods of the thermoelectric efficiency optimization are discussed.

Ruthenium intermetallics grown from La-Ni flux: synthesis, structure, and physical properties.

Crystals of three new intermetallic compounds were grown from reactions of ruthenium with other elements in La(0.8)Ni(0.2) eutectic flux. The new boride LaRu(2)Al(2)B crystallizes in a filled CeMg(2)Si(2) structure type (P4/mmm, a = 4.2105(5) A, c = 5.6613(8); Z = 1, R(1) = 0.014), with Ru atoms forming a planar square net; B atoms center alternating Ru squares, which is an unusual coordination of boron by transition metals. Al atoms connect the Ru(2)B layers, forming large voids where La ions reside. The chemical bonding analysis using the electron localization function (ELF) reveals two-center covalent bonding between Al atoms, an absence of direct Ru-Ru interactions, and three-centered bonds between Ru and B or Al atoms. The band structure calculation shows LaRu(2)Al(2)B to be metallic, which is in agreement with the observed temperature independent paramagnetism and heat capacity data. The crystal structure of La(2)Ni(2-x)Ru(x)Al (HT-Pr(2)Co(2)Al-type; x = 0.21(1) and x = 0.76(1); C2/c; a = 9.9001(3) A, b = 5.7353(1) A, c = 7.8452(2) A, beta = 104.275(1); Z = 4, R(1) = 0.016 for x = 0.76(1)) features infinite [Ni(2-x)Ru(x)Al] spiral-twisted chains composed of Al(2)M(2)-rhombic units (M = Ni/Ru) seen in many La-Ni-Al intermetallics. The structure of La(6)SnNi(3.67)Ru(0.76)Al(3.6) (Nd(6)Co(5)Ge(2.2)-type; P6m2, a = 9.620(1) A, c = 4.2767(9) A; Z = 1, R(1) = 0.015) is composed of a three-dimensional [Ni(3.67)Ru(0.76)Al(3.6)](3)(infinity) network with large hexagonal channels accommodating interconnected tin-centered lanthanum clusters Sn@La(9).