Control of the Iridium Oxidation State in the Hollandite Iridate Solid Solution K_1–<i>x</i>Ir₄O₈

The synthesis and physical properties of the K_1–<i>x</i>Ir₄O₈ (0 ≤ <i>x</i> ≤ 0.7) solid solution are reported. The structure of KIr₄O₈, solved with single-crystal X-ray diffraction at <i>T</i> = 110 K, is found to be tetragonal, space group <i>I</i>4/<i>m</i>, with <i>a</i> = 10.0492(3) Å and <i>c</i> = 3.14959(13) Å. A highly anisotropic displacement parameter is found for the potassium cation. Density functional theory calculations suggest that this anisotropy is due to a competition between atomic size and bond valence. KIr₄O₈ has a significant electronic contribution to the specific heat, γ = 13.9 mJ mol-Ir^–1 K^–2, indicating an effective carrier mass of m*/m_e ≈ 10. Further, there is a magnetic-field-dependent upturn in the specific heat at <i>T</i> < 3 K, suggestive of a magnetically sensitive phase transition below <i>T</i> < 1.8 K. Resistivity and magnetization measurements show that both end-members of the solid solution, KIr₄O₈ and K_1–<i>x</i>Ir₄O₈ (<i>x</i> ≈ 0.7), are metallic, with no significant trends in the temperature-independent contributions to the magnetization. These results are interpreted and discussed in the context of the importance of the variability of the oxidation state of iridium. The differences in physical properties between members of the K_1–<i>x</i>Ir₄O₈ (0 ≤ <i>x</i> ≤ 0.7) series are small and appear to be insensitive to the iridium oxidation state

Adventures in Crystal Growth: Synthesis and Characterization of Single Crystals of Complex Intermetallic Compounds

The central motivation of this manuscript is to highlight the discovery of novel, highly correlated electron systems. Ternary phases with unusual ground states composed of lanthanides, transition metals, and main group elements exhibit competing behavior leading to potentially novel physical properties. These systems are known to exhibit exotic properties such as unconventional superconductivity, heavy fermion behavior, and unusual forms of magnetism. The flux-growth method provides an avenue to discover and grow large single crystalline materials so that structure–physical property relationships may be determined. The growth of high quality single crystals is necessary to elucidate the intrinsic magnetic, electronic, and thermodynamic properties and has played a significant role in advancing basic and applied materials research. In this manuscript, we review the crystal structures, physical properties, and structure–property correlations of a select group of intermetallic compounds to demonstrate the potential for growth and discovery of materials using main group flux

Discovery of Spin Glass Behavior in Ln₂Fe₄Sb₅ (Ln = La–Nd and Sm)

Single crystals of Ln₂Fe₄Sb₅ (Ln = La–Nd and Sm) were grown from an inert Bi flux. Measurements of the single crystal X-ray diffraction revealed that these compounds crystallize in the tetragonal space group <i>I</i>4/<i>mmm</i> with lattice parameters of <i>a</i> ≈ 4 Å, <i>c</i> ≈ 26 Å, <i>V</i> ≈ 500 ų, and <i>Z</i> = 2. This crystal structure consists of alternating LnSb₈ square antiprisms and Fe-sublattices composed of nearly equilateral triangles of bonded Fe atoms. These compounds are metallic and display spin glass behavior, which originates from the magnetic interactions within the Fe-sublattice. Specific heat measurements are void of any sharp features that can be interpreted as contributions from phase transitions as is typical for spin glass systems. A large, approximately linear in temperature, contribution to the specific heat of La₂Fe₄Sb₅ is observed at low temperatures that we interpret as having a magnetic origin. Herein, we report the synthesis, structure, and physical properties of Ln₂Fe₄Sb₅ (Ln = La–Nd and Sm)

Crystal Growth, Structure, and Physical Properties of LnCu₂(Al,Si)₅ (Ln = La and Ce)

LnCu₂(Al,Si)₅ (Ln = La and Ce) were synthesized and characterized. These compounds adopt the SrAu₂Ga₅ structure type and crystallize in the tetragonal space group <i>P</i>4/<i>mmm</i> with unit cell dimensions of <i>a</i> ≈ 4.2 Å and <i>c</i> ≈ 7.9 Å. Herein, we report the structure as obtained from single crystal X-ray diffraction. Additionally, we report the magnetic susceptibility, magnetization, resistivity, and specific heat capacity data obtained for polycrystalline samples of LnCu₂(Al,Si)₅ (Ln = La and Ce)

Stacking Variants and Superconductivity in the Bi–O–S System

High-temperature superconductivity has a range of applications from sensors to energy distribution. Recent reports of this phenomenon in compounds containing electronically active BiS₂ layers have the potential to open a new chapter in the field of superconductivity. Here we report the identification and basic properties of two new ternary Bi–O–S compounds, Bi₂OS₂ and Bi₃O₂S₃. The former is non-superconducting; the latter likely explains the superconductivity at <i>T</i>_c = 4.5 K previously reported in “Bi₄O₄S₃”. The superconductivity of Bi₃O₂S₃ is found to be sensitive to the number of Bi₂OS₂-like stacking faults; fewer faults correlate with increases in the Meissner shielding fractions and <i>T</i>_c. Elucidation of the electronic consequences of these stacking faults may be key to the understanding of electronic conductivity and superconductivity which occurs in a nominally valence-precise compound

Crystal Growth, Structure, and Physical Properties of LnCu₂(Al,Si)₅ (Ln = La and Ce)

LnCu₂(Al,Si)₅ (Ln = La and Ce) were synthesized and characterized. These compounds adopt the SrAu₂Ga₅ structure type and crystallize in the tetragonal space group <i>P</i>4/<i>mmm</i> with unit cell dimensions of <i>a</i> ≈ 4.2 Å and <i>c</i> ≈ 7.9 Å. Herein, we report the structure as obtained from single crystal X-ray diffraction. Additionally, we report the magnetic susceptibility, magnetization, resistivity, and specific heat capacity data obtained for polycrystalline samples of LnCu₂(Al,Si)₅ (Ln = La and Ce)

Synthesis, Structure, and Physical Properties of <i>Ln</i>(Cu,Al,Ga)_{13–<i>x</i>} (<i>Ln</i> = La–Pr, and Eu) and Eu(Cu,Al)_{13–<i>x</i>}

<i>Ln</i>(Cu,Al,Ga)_{13–<i>x</i>} (<i>Ln</i> = La–Pr, and Eu; <i>x</i> ∼ 0.2) were synthesized by a combined Al/Ga flux. Single crystal X-ray and neutron diffraction experiments revealed that these compounds crystallize in the NaZn₁₃ structure-type (space group <i>Fm</i>3̅<i>c</i>) with lattice parameters of <i>a</i> ∼ 12 Å, <i>V</i> ∼ 1600 Å, and <i>Z</i> ∼ 8. Our final neutron models led us to conclude that Cu is occupationally disordered on the 8<i>b</i> Wyckoff site while Cu, Al, and Ga are substitutionally disordered on the 96<i>i</i> Wyckoff site of this well-known structure-type. The magnetic susceptibility data show that Ce­(Cu,Al,Ga)_{13–<i>x</i>} and Pr­(Cu,Al,Ga)_{13–<i>x</i>} exhibit paramagnetic behavior down to the lowest temperatures measured while Eu­(Cu,Al,Ga)_{13–<i>x</i>} displays ferromagnetic behavior below 6 K. Eu­(Cu,Al)_{13–<i>x</i>} was prepared via arc-melting and orders ferromagnetically below 8 K. The magnetocaloric properties of Eu­(Cu,Al,Ga)_{13–<i>x</i>} and Eu­(Cu,Al)_{13–<i>x</i>} were measured and compared. Additionally, an enhanced value of the Sommerfeld coefficient (γ = 356 mJ/mol-K²) was determined for Pr­(Cu,Al,Ga)_{13–<i>x</i>}. Herein, we present the synthesis, structural refinement details, and physical properties of <i>Ln</i>(Cu,Al,Ga)_{13–<i>x</i>} (<i>Ln</i> = La–Pr, and Eu) and Eu­(Cu,Al)_{13–<i>x</i>}