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

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

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

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

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

Prediction of Van Hove singularity systems in ternary borides

A computational search for stable structures among both $\alpha$ and $\beta$ phases of ternary ATB4 borides (A= Mg, Ca, Sr, Ba, Al, Ga, and Zn, T is 3d or 4d transition elements) has been performed. We found that $\alpha$-ATB4 compounds with A=Mg, Ca, Al, and T=V, Cr, Mn, Fe, Ni, and Co form a family of structurally stable or almost stable materials. These systems are metallic in non-magnetic states and characterized by the formation of the localized molecular-like state of 3d transition metal atom dimers, which leads to the appearance of numerous Van Hove singularities (VHS) in the electronic spectrum. The closeness of these VHS to the Fermi level can be easily tuned by electron doping. For the atoms in the middle of the 3d row (Cr, Mn, and Fe), these VHS led to magnetic instabilities and new magnetic ground states with a weakly metallic or semiconducting nature. The magnetic ground states in these systems appear as an analog of the spin glass state. Experimental attempts to produce MgFeB4 and associated challenges are discussed, and promising directions for further synthetic studies are formulated.Comment: 9 figure

Ba2Si3P6: 1D Nonlinear Optical Material with Thermal Barrier Chains

A novel barium silicon phosphide was synthesized and characterized. Ba2Si3P6 crystallizes in the noncentrosymmetric space group Pna21 (No. 33) and exhibits a unique bonding connectivity in the Si–P polyanion not found in other compounds. The crystal structure is composed of SiP4 tetrahedra connected into one-dimensional double-tetrahedra chains through corner sharing, edge sharing, and covalent P–P bonds. Chains are surrounded by Ba cations to achieve an electron balance. The novel compound exhibits semiconducting properties with a calculated bandgap of 1.6 eV and experimental optical bandgap of 1.88 eV. The complex pseudo-one-dimensional structure manifests itself in the transport and optical properties of Ba2Si3P6, demonstrating ultralow thermal conductivity (0.56 W m–1 K–1 at 300 K), promising second harmonic generation signal (0.9 × AgGaS2), as well as high laser damage threshold (1.6 × AgGaS2, 48.5 MW/cm2) when compared to the benchmark material AgGaS2. Differential scanning calorimetry reveals that Ba2Si3P6 melts congruently at 1373 K, suggesting that large single crystal growth may be possible

Crystal and Electronic Structure and Optical Properties of AE2SiP4 (AE = Sr, Eu, Ba) and Ba4Si3P8

Three new compounds in the AE‐Si‐P (AE = Sr, Eu, Ba) systems are reported. Sr2SiP4 and Eu2SiP4, the first members of their respective ternary systems, are isostructural to previously reported Ba2SiP4 and crystallize in the noncentrosymmetric I42d (no. 122) space group. Ba4Si3P8 crystallizes in the new structure type, in P21/c (no. 14) space group, mP‐120 Pearson symbol, Wyckoff sequence e30. In the crystal structures of Sr2SiP4 and Eu2SiP4 all SiP4 tetrahedral building blocks are connected via formation of P–P bonds forming a three‐dimensional framework. In the crystal structure of Ba4Si3P8, Si‐P tetrahedral chains formed by corner‐sharing, edge‐sharing, and P–P bonds are surrounded by Ba cations. This results in a quasi‐one‐dimensional structure. Electronic structure calculations and UV/Vis measurements suggest that the AE2SiP4 (AE = Sr, Eu, Ba) are direct bandgap semiconductors with bandgaps of ca. 1.4 eV and have potential for thermoelectric applications