Structural Phase Transitions in a New Compound Eu₂AgGe₃

A new intermetallic compound Eu₂AgGe₃ has been synthesized using high-frequency induction heating method. Single-crystal X-ray diffraction data showed that Eu₂AgGe₃ crystallizes in the orthorhombic Ba₂LiSi₃ structure type, with <i>Fddd</i> space group and lattice parameters <i>a</i> = 8.7069(17) Å, <i>b</i> = 15.011(3) Å, <i>c</i> = 17.761(4) Å. Eu₂AgGe₃ is composed of infinite arrays of hexagonal [Ag₃Ge₃] units stacked along the [001] direction, and the Eu sites are sandwiched between these parallel hexagonal networks. Temperature-dependent powder XRD data and DTA hint toward a structural phase transition from orthorhombic to hexagonal above 477 K and an unusual reversible transition to the original phase, i.e., orthorhombic phase at around 718 K. Magnetic measurements on Eu₂AgGe₃ sample show paramagnetic behavior above 100 K and weak ferromagnetic interactions below 80 K. Mössbauer spectroscopy and X-ray absorption near-edge spectroscopic (XANES) studies reveal that Eu atoms in Eu₂AgGe₃ exist in the divalent oxidation state

Metallic Yb₂AuGe₃: An Ordered Superstructure in the AlB₂‑Type Family with Mixed-Valent Yb and a High-Temperature Phase Transition

The intermetallic compound Yb₂AuGe₃ was synthesized from indium flux. Yb₂AuGe₃ crystallizes in the orthorhombic Ca₂AgSi₃-type structure which is an ordered superstructure of the AlB₂ structure type. The structure was refined in the <i>Fmmm</i> space group with lattice parameters <i>a</i> = 8.5124(17) Å, <i>b</i> = 14.730(3) Å, <i>c</i> = 8.4995(17) Å. Temperature-dependent powder X-ray diffraction studies show that Yb₂AuGe₃ undergoes a phase transition from orthorhombic to hexagonal upon heating above 773 K. The compound shows weak paramagnetism that derives from a combination of Curie and Pauli paramagnetism with a magnetic moment value of 0.33(2) μ_B/Yb atom. Magnetic ordering was not observed down to 2 K. Yb₂AuGe₃ is metallic, and at low temperature the resistivity varies as <i>T</i>², indicating possible Fermi liquid behavior. Heat capacity measurements suggest that Yb₂AuGe₃ is possibly a moderate heavy fermion system

Metallic Yb₂AuGe₃: An Ordered Superstructure in the AlB₂‑Type Family with Mixed-Valent Yb and a High-Temperature Phase Transition

The intermetallic compound Yb₂AuGe₃ was synthesized from indium flux. Yb₂AuGe₃ crystallizes in the orthorhombic Ca₂AgSi₃-type structure which is an ordered superstructure of the AlB₂ structure type. The structure was refined in the <i>Fmmm</i> space group with lattice parameters <i>a</i> = 8.5124(17) Å, <i>b</i> = 14.730(3) Å, <i>c</i> = 8.4995(17) Å. Temperature-dependent powder X-ray diffraction studies show that Yb₂AuGe₃ undergoes a phase transition from orthorhombic to hexagonal upon heating above 773 K. The compound shows weak paramagnetism that derives from a combination of Curie and Pauli paramagnetism with a magnetic moment value of 0.33(2) μ_B/Yb atom. Magnetic ordering was not observed down to 2 K. Yb₂AuGe₃ is metallic, and at low temperature the resistivity varies as <i>T</i>², indicating possible Fermi liquid behavior. Heat capacity measurements suggest that Yb₂AuGe₃ is possibly a moderate heavy fermion system

Crystal Structure and Magnetic Properties of Indium Flux Grown EuAu₂In₄ and EuAuIn₄

Two new intermetallic compounds EuAuIn₄ and EuAu₂In₄ having plate- and rodlike shapes, respectively, were synthesized using indium as an active metal flux. Both compounds crystallize in the orthorhombic system and can be classified as polyindide systems due to the presence of [In₄] tetrameric units. EuAuIn₄ adopts the YNiAl₄ structure type with <i>Cmcm</i> space group and lattice parameters <i>a</i> = 4.6080(3) Å, <i>b</i> = 17.0454(8) Å, <i>c</i> = 7.5462(4). EuAu₂In₄ crystallizes in the NdRh₂Sn₄ structure type with <i>Pnma</i> space group and lattice parameters <i>a</i> = 18.5987(7) Å, <i>b</i> = 4.6616(2) Å, and <i>c</i> = 7.4669(3) Å. EuAuIn₄ consists of three-dimensional [AuIn₄] units, and the europium atoms reside in the distorted hexagonal channels, whereas, in EuAu₂In₄, the europium atoms are enclosed by three-dimensional cages of [Au₂In₄] polyanionic units. Magnetic susceptibility measurements showed Curie–Weiss behavior within the temperature range of 80–300 K for EuAu₂In₄ and 10–300 K for EuAu₂In₄ with an effective magnetic moment (μ_eff) of 5.88 and 7.76 μ_B/Eu atom, respectively. The negative Curie–Weiss paramagnetic temperature in both compounds suggests antiferromagnetic interactions

Facile Aqueous-Phase Synthesis of the PtAu/Bi₂O₃ Hybrid Catalyst for Efficient Electro-Oxidation of Ethanol

In this work, we present a facile aqueous-phase synthesis of a hybrid catalyst consisting of PtAu alloy supported on Bi₂O₃ microspheres. Multistep reduction of HAuCl₄ and K₂PtCl₄ salts on Bi₂O₃ and subsequent annealing lead to the formation of this hybrid catalyst. To the best of our knowledge, this is the first report of using Bi₂O₃ as a catalyst support in fuel cell applications. The material was characterized by powder X-ray diffraction and various microscopic techniques. This composite showed remarkable activity as well as stability toward the electro-oxidation of ethanol in comparison to commercially available Pt/C. The order of the reactivity was found to be commercial Pt/C (50.4 mA/m²mg_Pt^–1) < Pt/Bi₂O₃(10) (108 mA/m²mg_Pt^–1) < PtAu/Bi₂O₃(10) (459 mA/m²mg_Pt^–1). The enhancement in the activity can be explained through cooperative effects, namely, ligand effects of gold and Bi₂O₃ support, which helps in removing carbon monoxide molecules to avoid the poisoning of the Pt active sites

Yb₅Ga₂Sb₆: A Mixed Valent and Narrow-Band Gap Material in the RE₅M₂X₆ Family

A new compound Yb₅Ga₂Sb₆ was synthesized by the metal flux technique as well as high frequency induction heating. Yb₅Ga₂Sb₆ crystallizes in the orthorhombic space group <i>Pbam</i> (no. 55), in the Ba₅Al₂Bi₆ structure type, with a unit cell of <i>a</i> = 7.2769(2) Å, <i>b</i> = 22.9102(5) Å, <i>c</i> = 4.3984(14) Å, and <i>Z</i> = 2. Yb₅Ga₂Sb₆ has an anisotropic structure with infinite anionic double chains (Ga₂Sb₆)^10– cross-linked by Yb²⁺ and Yb³⁺ ions. Each single chain is made of corner-sharing GaSb₄ tetrahedra. Two such chains are bridged by Sb₂ groups to form double chains of 1/∞ [Ga₂Sb₆^10–]. The compound satisfies the classical Zintl–Klemm concept and is a narrow band gap semiconductor with an energy gap of around 0.36 eV calculated from the electrical resistivity data corroborating with the experimental absorption studies in the IR region (0.3 eV). Magnetic measurements suggest Yb atoms in Yb₅Ga₂Sb₆ exist in the mixed valent state. Temperature dependent magnetic susceptibility data follows the Curie–Weiss behavior above 100 K and no magnetic ordering was observed down to 2 K. Experiments are accompanied by all electron full-potential linear augmented plane wave (FP-LAPW) calculations based on density functional theory to calculate the electronic structure and density of states. The calculated band structure shows a weak overlap of valence band and conduction band resulting in a pseudo gap in the density of states revealing semimetallic character

Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic–Organic Hybrids

We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations

Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic–Organic Hybrids

We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations

Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic–Organic Hybrids

We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations

Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic–Organic Hybrids

We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations