Minority report : Structure and bonding of YbNi3Ga9 and YbCu3Ga8 obtained in gallium flux

The gallides YbNi3Ga9 and YbCu3Ga8 were obtained from flux growth reactions of Yb, various transition metals M, and Ga, to test a stability diagram that predicts the formation of ternary intermetallic phases. The structure of YbNi3Ga9 was redetermined to resolve discrepancies in the literature. For an untwinned crystal of YbNi3Ga9, the ErNi3Al9-type structure was confirmed (space group R32, a ​= ​7.2294(7) Å, c ​= ​27.513(3) Å, Z ​= ​6), giving rise to an ordered arrangement of Yb2Ga3 nets in the stacking sequence. Crystals of YbCu3Ga8 were among the minority formed in the flux growth reaction. YbCu3Ga8 adopts the rare BaHg11-type structure (space group Pm3¯m, a ​= ​8.2818(13) Å, Z ​= ​3), with Cu and Ga atoms assumed to be disordered. As examples of polar intermetallics, these compounds exhibit electron transfer from Yb to Ga atoms, which then form multicentre covalent bonding networks, as confirmed by electronic structure calculations

Anisotropic Near-Zero Thermal Expansion in REAgxGa4–x\mathrm{REAg_{x}Ga_{4–x}} ( RE = La–Nd, Sm, Eu, and Yb) Induced by Structural Reorganization

n this work, we have discovered the anisotropic near-zero thermal expansion (NZTE) behavior in a family of compounds REAg$_x$Ga$_{4–x}$ (RE = La–Nd, Sm, Eu, and Yb). The compounds adopt the CeAl$_2$Ga$_2$ structure type and were obtained as single crystals in high yield by metal flux growth technique using gallium as active flux. Temperature-dependent single crystal X-ray diffraction suggests that all the compounds exhibit near zero thermal expansion along c direction in the temperature range of 100–450 K. Temperature-dependent X-ray absorption near-edge spectroscopic study confirmed ZTE behavior is due to the geometrical features associated within the crystal structure. The anisotropic NZTE behavior was further established by anisotropic magnetic measurements on selected single crystals. The atomic displacement parameters, apparent bond lengths, bond angles, and structural distortion with respect to the temperature reveal that geometric features associated with the structural distortion cause the anisotropic NZTE along c-direction. The preliminary magnetic studies suggest all the compounds are paramagnetic at room temperature except LaAgGa$_3$. Electrical resistivity study reveals that compounds from this series are metallic in nature

Metal Deficiency Tailored by the 18-Electron Rule Stabilizes Metal-Based Inorganic Compounds

The 18-electron (18-$e^–$) rule is typically restricted to predicting the stability of transition-metal-based complexes. Herein, we report the use of the 18-$e^–$ to predict the stability in a family of intermetallics MNiSn (M = V, Cr, Fe, and Co) crystallizing in the Co$_{1.75}$Ge structure type. Site deficiencies at the M site obtained from single-crystal X-ray diffraction are understood as attaining a stable noble gas electronic configuration. The density functional theory -based structure calculation confirms that the deficient structure is more stable than the ideal occupation available at the crystal lattice. MnNiSn, which crystallizes in the half-Heusler crystal structure, depicts the role of covalent radii of the constituent elements in determining the crystal structure. Using X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, the local structure of the above-mentioned compounds was also elucidated, supporting the role of deficiency tuned valence fluctuation to attain a 18-$e^–$ configuration that eventually leads to the formation of stable compounds

Effect of aliovalent bismuth substitution on structure and optical properties of CsSnBr3

Abstract Aliovalent substitution of the B component in ABX 3 metal halides has often been proposed to modify the band gap and thus the photovoltaic properties, but details about the resulting structure have remained largely unknown. Here, we examine these effects in Bi-substituted CsSnBr3. Powder X-ray diffraction (XRD) and solid-state 119Sn, 133Cs and 209Bi nuclear magnetic resonance (NMR) spectroscopy were carried out to infer how Bi substitution changes the structure of these compounds. The cubic perovskite structure is preserved upon Bi-substitution, but with disorder in the B site occurring at the atomic level. Bi atoms are randomly distributed as they substitute for Sn atoms with no evidence of Bi segregation. The absorption edge in the optical spectra shifts from 1.8 to 1.2 eV upon Bi-substitution, maintaining a direct band gap according to electronic structure calculations. It is shown that Bi-substitution improves resistance to degradation by inhibiting the oxidation of Sn

Complex Crystal Chemistry of Yb6(CuGa)50\mathrm{Yb_{6}(CuGa)_{50}} and Yb6(CuGa)51\mathrm{Yb_{6}(CuGa)_{51}} Grown at Different Synthetic Conditions

Two new compounds in the Yb–Cu–Ga system were discovered. Yb$_6$(CuGa)$_{50}$ was obtained as single crystals grown from gallium metal flux, and Yb$_6$(CuGa)$_{51}$ was synthesized by high-frequency induction heating technique. Structure analysis reveals new structure type for Yb$_6$(CuGa)$_{50}$ (C2/m space group), while Yb$_6$(CuGa)$_{51}$ crystallizes in rhombohedral space group R3̅m adopting the Th$_{2Z}$n$_{17}$ structure type. Both structures could be derived from the simplest layered packing, through CaCu$_5$-type structure, as a common parent. Physical properties of the Yb$_6$(CuGa)$_{51}$ sample obtained bulk quantity were explored. The magnetic susceptibility study of Yb$_6$(CuGa)$_{51}$ in the temperature range of 2–300 K suggests a valence fluctuation at lower temperatures. X-ray absorption near edge spectroscopy suggests that Yb exists in mixed-valent state in Yb$_6$(CuGa)$_{51}$. Electrical resistivity measurement reveals that Yb$_6$(CuGa)$_{51}$ is metallic in nature and shows Fermi-liquid behavior in the temperature range from 3.5 to 25 K

Crystal Engineering in Supramolecular Polyoxometalate Hybrids through pH Controlled in Situ Ligand Hydrolysis

A family of five different three-dimensional polyoxometalate (POM) based supramolecular hybrids were synthesized by a hydrothermal route under different pH using a hydrolyzable naphthalene diimide ligand. The mechanism of crystallographic phase variation of the POM-amino pyridine hybrids under different pH was studied through controlled experiments where the final hydrolyzed products were analyzed through NMR and single crystal X-ray diffraction. Different pH conditions led to variation in the extent of protonation and hydrolyzation of the ligand, yielding different phases. All of these were identified, and the structures of the supramolecular hybrids were characterized extensively. Mechanistic study proved that only the reaction conditions are responsible for the hydrolysis of the ligand and the in situ generated POM species do not have any role in it. Magnetic measurements confirmed the hexavalent oxidation states of the transition metal center (Mo) in the POM. Optical band gap measurements revealed that these hybrids are semiconducting in nature. Two of the compounds were studied for hydrogen peroxide mediated selective oxidation catalysis of small organic molecules and found to exhibit very good activity with high percentage of selectivity for the desired products of industrial importance

Optimized Metal Deficiency-Induced Operando Phase Transformation Enhances Charge Polarization Promoting Hydrogen Evolution Reaction

Electrochemical water reduction is one of the cleanest ways to produce hydrogen efficiently. Non-noble metal-based intermetallic compounds, particularly Ni-based ones, can be projected as potential water electrocatalysts because of Ni’s low cost and high abundance. In this work, Ni’s crystal structure and electronic properties have been tuned by introducing Sn metal followed by operando structural transformation. The synthetically tuned deficiency of Ni in Ni$_{2–x}$Sn (x = 0.35, 0.50, and 0.63) and operando-induced phase transformation of the room temperature orthorhombic Cmcm space group (Ni$_{2–x}$Sn_RT) to the high-temperature hexagonal P6$_3$/mmc space group (Ni$_{2–x}$Sn_HT) enhance the hydrogen evolution. Several controlled synthesis and electrochemical measurements indicate that Ni$_{1.5}$Sn_HT is the most active and stable HER catalyst because of its unique crystallographic structure and high charge transfer kinetics. The phase Ni$_{1.5}$Sn_RT was electrochemically transformed to the HT phase during the HER process and found to be extremely stable (150 h) in the chronoamperometric study

Optimized Metal Deficiency-Induced Operando Phase Transformation Enhances Charge Polarization Promoting Hydrogen Evolution Reaction

Electrochemical water reduction is one of the cleanest ways to produce hydrogen efficiently. Non-noble metal-based intermetallic compounds, particularly Ni-based ones, can be projected as potential water electrocatalysts because of Ni’s low cost and high abundance. In this work, Ni’s crystal structure and electronic properties have been tuned by introducing Sn metal followed by operando structural transformation. The synthetically tuned deficiency of Ni in Ni2–xSn (x = 0.35, 0.50, and 0.63) and operando-induced phase transformation of the room temperature orthorhombic Cmcm space group (Ni2–xSn_RT) to the high-temperature hexagonal P63/mmc space group (Ni2–xSn_HT) enhance the hydrogen evolution. Several controlled synthesis and electrochemical measurements indicate that Ni1.5Sn_HT is the most active and stable HER catalyst because of its unique crystallographic structure and high charge transfer kinetics. The phase Ni1.5Sn_RT was electrochemically transformed to the HT phase during the HER process and found to be extremely stable (150 h) in the chronoamperometric study

Controlling the Luminescence of Rare-Earth Chalcogenide Iodides <i>RE</i>₃(Ge_1–<i>x</i>Si_<i>x</i>)₂S₈I (<i>RE</i> = La, Ce, and Pr) and Ce₃Si₂(S_1–<i>y</i>Se_<i>y</i>)₈I

The rare-earth chalcogenide iodides RE3(Ge1–xSix)2S8I (RE = La, Ce, and Pr) and Ce3Si2(S1–ySey)8I were prepared by reactions of the elements at 900 °C. Phase-pure samples and complete solid solutions were obtained for all series, as determined by powder X-ray diffraction patterns, with the cell parameters evolving smoothly. They adopt the monoclinic La3Si2O8Cl-type structure (space group C2/c), containing isolated tetrahedra centered by the tetrel atoms and separated by the RE and I atoms. Single-crystal X-ray diffraction studies indicate that substitution of Si for Ge atoms in RE3(Ge1–xSix)2S8I leads to complete disorder of the tetrel atoms, whereas partial substitution of Se for S atoms in Ce3Si2(S1–ySey)8I occurs with preferential occupation of Se atoms. The optical band gaps increase slightly upon substitution with Si in RE3(Ge1–xSix)2S8I (or negligibly in the case of the Ce-containing series, remaining at 2.8 eV), and they decrease dramatically upon substitution with Se in Ce3Si2(S1–ySey)8I, from 2.8 to 1.9 eV. These band gaps are direct according to electronic structure calculations. The strong blue photoluminescence emission in Ce3Si2S8I shifts slightly to blue-green in Ce3(Ge0.25Si0.75)2S8I and significantly to green in Ce3Si2(S0.81Se0.19)8I, as quantified by their chromaticity coordinates. Increasing the concentration of Ge or Se tends to decrease the photoluminescence intensity and lifetime. For Ce3Si2S8I, the activation energy for thermal quenching is 0.68 eV