High Pressure Properties of a Ba-Cu-Zn-P Clathrate-I.

The high pressure properties of the novel tetrel-free clathrate, Ba₈Cu13.1Zn3.3P29.6, were investigated using synchrotron powder X-ray diffraction. The pressure was applied using a diamond anvil cell. No structural transitions or decomposition were detected in the studied pressure range of 0.1-7 GPa. The calculated bulk modulus for Ba₈Cu13.1Zn3.3P29.6 using a third-order Birch-Murnaghan equation of state is 65(6) GPa at 300 K. This bulk modulus is comparable to the bulk moduli of Ge- and Sn-based clathrates, like A₈Ga16Ge30 (A = Sr, Ba) and Sn19.3Cu4.7P22I₈, but lower than those for the transition metal-containing silicon-based clathrates, Ba₈TxSi46-x, T = Ni, Cu; 3 ≤ x ≤ 5

Tris(ethyl-enedi-amine)-cobalt(II) dichloride.

The title compound, [Co(II)(C2H8N2)3]Cl2, was obtained unexpectedly as the product of an attempted solvothermal synthesis of cobalt selenide from the elements in the presence of NH4Cl in ethyl-enedi-amine solvent. The three chelate rings of the distorted octa-hedral [Co(C2H8N2)3](2+) complex cation adopt twisted conformations about their C-C bonds. The spread of cis-N-Co-N bond angles [80.17 (6)-98.10 (6)°] in the title compound is considerably greater than the equivalent data for [Co(III)(C2H8N2)3]Cl3 [Takamizawa et al. (2008 ▶). Angew. Chem. Int. Ed. 47, 1689-1692]. In the crystal, the components are linked by numerous N-H⋯Cl hydrogen bonds, generating a three-dimensional network in which the cationic complexes are stacked in columns along [010] and separated by columns of chloride anions

Synthesis and Characterization of K and Eu Binary Phosphides.

The synthesis, structural characterization, and optical properties of the binary Zintl phases of α-EuP₃, β-EuP₃, EuP₂, and α-K₄P₆ are reported in this study. These crystal structures demonstrate the versatility of P fragments with dimensionality varying from 0D (P₆ rings in α-K₄P₆) to 1D chains (EuP₂) to 2D layers (both EuP₃). EuP₂ is isostructural to previously reported SrP₂ and BaP₂ compounds. The thermal stabilities of the EuP₂ and both EuP₃ phases were determined using differential scanning calorimetry (DSC), with melting temperatures of 1086 K for the diphosphide and 1143 K for the triphosphides. Diffuse reflectance spectroscopy indicated that EuP₂ is an indirect semiconductor with a direct bandgap of 1.12(5) eV and a smaller indirect one, less than 1 eV. Both EuP₃ compounds had bandgaps smaller than 1 eV

Estudo anatômico e palinológico de Antônia ovata Pohl (Loganiaceae)

Nesta comunicação o autor considera a anatomia do caule, pecíolo, lâmina foliar e madeira, além dos aspectos morfológicos externo e palinológico, de espécimes de Antonia ovata, ocorrentes na floresta da região do rio Jarí (Estado do Pará) e nos cerrados da Amazônia e do Brasil Central; nomeia os espécimes da mata como sendo uma variedade nova para a ciência: Antonia ovata Pohl var. excelsa Paula.In this paper the author studies extern morphological, palinological and anatomical aspects, aiming to put an end to the doubts in the taxonomic studies of the specimens of Antonia ovata Pohl (or aiming make clear the taxonomy of the specimens of Antonia ovata. Specimens of Antonia ovata from the woods of the region of Jarí river (Amazônia) are considered by the author as a new variety. With its description, the number of varieties of Antonia ovata rose to three: pilosa, ovata and excelsa (new variety). The extern morphological aspect is found among the individuals from three habitats: "cerrados" of Amazônia, Brasil Central and forest of the region Jarí river. The identification of the three varieties is based on the following characteristic. Presence or lack of hairs on the leaves and branches; microscopic structure of wood (see comparative table); height and diameter of the specimens; and finally the habitat. Pollen grains of these two varieties excelsa and ovata present polymorphism. The leaf of that species has structure of a higrophyllous plants. The stem is rich in mucilaginous cells; vascular bundles are bicollateral; the leafknot is bilacunar, and the trace is formed by two vascular bundles

Electrocatalytic performance and stability of nanostructured Fe–Ni pyrite-type diphosphide catalyst supported on carbon paper

A simple and effective method to prepare an active and stable nanostructured working electrode for electrochemical water splitting is described. Specifically, mixed Fe–Ni diphosphide was prepared by sputtering a 200-nm-thick layer of Permalloy onto carbon paper gas diffusion layer followed by gas transport phosphorization reaction. The mass density of the resultant diphosphide phase was established to be 1.1 mg/cm2. Energy-dispersive X-ray microanalysis shows that the actual elemental composition of the resultant ternary electrocatalyst is approximately Fe0.2Ni0.8P2, while the powder X-ray diffraction analysis confirms that the electrocatalyst crystallizes in NiP2 cubic pyrite-like structure. As a cathode for hydrogen evolution reaction (HER) in acidic and alkaline electrolytes, this earth-abundant electrode has exchange current densities of 6.84103 and 3.16103 mA/cm2 and Tafel slopes of 55.3 and 72.2 mV/dec, respectively. As an anode for oxygen evolution reaction (OER) in alkaline electrolyte, the electrode shows an exchange current density of 2.88104 mA/cm2 and Tafel slope of 49.3 mV/dec. The observed high activity of the electrode correlates well with its electronic structure, which was assessed by density functional theory (DFT) calculations. The stability of Fe0.2Ni0.8P2 electrocatalyst in HER and OER was evaluated by means of accelerated degradation test and chronopotentiometry. The results of these experiments elucidate partial dissolution and entire chemical transformation of Fe0.2Ni0.8P2 as the main mechanisms of the electrode degradation during HER and OER, respectively. Overall, our findings could facilitate the composition-based design of active, stable, and durable phosphide electrodes for electrochemical water splitting.We thank all members of the Nanomaterials Synthesis Unit at the INL for their fruitful scientific and technical input, as well as Dr. X. Wang for his help with the electrocatalytic data analysis. This investigation has benefited from the financial support provided by the European Union Horizon 2020 NMP programme through the CritCat project under grant agreement no. 686053, as well as ERDF funds through the Portuguese Operational Programme for Competitiveness and Internationalization (COMPETE 2020), and National Funds through the Portuguese Foundation for Science and Technology (FCT), under the PrintPV project PTDC/CTM-ENE/5387/2014 (grant agreement no. 016663). J.D.C. thanks the FCT PhD grant SFRH/BD/79393/2011, while J.L.L. thanks Marie-Curie-ITN607904-SPINOGRAPH project for the PhD grant

Flux Growth of Phosphide and Arsenide Crystals

Flux crystal growth has been widely applied to explore new phases and grow crystals of emerging materials. To accommodate the needs of high-quality single crystals, the flux crystal growth should be reliable, controllable, and predictable. The selections of suitable flux and growth conditions remain empirical due to the lack of systematic investigation especially for reactions, which involve highly volatile components, such as P and As. Considering the flux elements, often the system in question is a quaternary or a higher multinary system, which drastically increases complexity. In this manuscript, on the examples of flux growth of phosphides and arsenides, guidelines of flux selections, existing challenges, and future directions are discussed. We expect that the field will be further developed by applying in situ techniques and computational modeling of the nucleation and growth kinetics. Additionally, leveraging variables other than temperature, such as applied pressure, will make flux growth a more powerful tool in the future

Aliovalent substitutions of the 2D layered semiconductor GeAs

Layered tetrel pnictides have shown promise as thermoelectrics (TEs) due to their anisotropic crystal structure and weak van der Waals interactions between layers. The binary GeAs is a p-type semiconductor with a narrow indirect bandgap of 0.57 eV and a high Seebeck coefficient (∼250 μV/K at 300 K). This work probes the limits of the aliovalent substitutions of GeAs to modify charge carrier concentration. GaxGe1-xAs (x = 0.005, 0.01, and 0.02) and GeAs1-ySey (y = 0.01, 0.02, 0.03, and 0.05) samples were synthesized to study the structure-property relationships in this system. Hole doping of GeAs via Ga-substitution increases carrier concentration resulting in the decrease in both resistivity and Seebeck coefficient. Se-substituted samples show more complex behavior related to defect chemistry. Overall, the thermoelectric power factor (S2/ρ) was significantly enhanced (up to 89%) for Ga0.005Ge0.995As as compared to pristine GeAs

Phonon glass behavior beyond traditional cage structures: synthesis, crystal and electronic structure, and properties of KMg4Sb3

Three new ternary antimonides, KMg4Sb3 and A(2)Mg(5)Sb(4) (A - Rb, Cs), were synthesized via high-temperature solid-state reactions and their crystal structures were determined by single crystal X-ray diffraction. All three compounds feature three-dimensional anionic frameworks composed of edge-shared MgSb4 tetrahedra with channels trapping the alkali metal cations. KMg4Sb3 crystallizes in beta-BaCu4S3 structure type (Pearson symbol oS32) while Rb2Mg5Sb4 and Cs2Mg5Sb4 are isostructural and crystallize in K2Zn5As4 structure type (Pearson symbol oC44). Band structure calculations predict KMg4Sb3 to be a direct bandgap semiconductor with E-g of similar to 1 eV. Characterizations of the transport properties indicate that KMg4Sb3 is a semiconductor with impurity levels. KMg4Sb3 exhibits ultralow total thermal conductivity of 0.9 W m(-1) K-1 at 300 K. Potassium cations in the structure of KMg4Sb3 exhibit abnormally large anisotropic displacement parameters at 90 K, a behavior typical for rattling cations. Calculations of the phonon dispersions and density of states support the K rattling as an important contributor to overall thermal conductivity reduction. A Phonon-Glass thermal behavior with K atoms rattling in open channels of Mg4Sb3 framework shines new light on designing low thermal conductivity materials