High-pressure Synthesis of Ba2CoO2Ag2Te2 with Extended CoO2 Planes

Using a high-pressure synthesis method, we prepared the layered oxychalcogenide Ba₂CoO₂Ag₂Te₂ (space group: I4/mmm) with alternating stacks of CoO₂ and Ag₂Te₂ layers, separated by Ba atoms. The CoO₂ plane is greatly extended (Co-O = 2.19 Å on average) due to tensile strain from adjacent Ag₂Te₂ layers, causing displacement of oxide anions. Layered cobaltates with trans-CoO₄X₂ (X = chalcogen, halogen) coordination feature large spin-orbit coupling, which is linearly scaled by the tetrahedral factor of d_Co-X/d_Co-O. However, applying this relation to Ba₂CoO₂Ag₂Te₂ yields a magnetic moment of ∼4 μ_B, which is nearly twice the experimentally observed value of 1.87(17) μ_B. This result, along with a reduced Néel temperature (T_N = 60 K), originates from the off-centered position of otherwise under-bonded oxide anions, which changes the crystal field splitting of Co d orbitals.

An unprecedented pentanary chalcohalide with Mn atoms in two chemical environments: unique bonding characteristics and magnetic properties

An unprecedented 2D layered pentanary chalcohalide Cs₂[Mn₂Ga₃S₇Cl] features distinguishing structure characteristics with the coexistence of two Mn-coordinated polyhedra and shows interesting ferrimagnetic behaviour.

Peculiar phase diagram with isolated superconducting regions in ThFeAsN1-x O x

ThFeAsN_1-x O _x ([Formula: see text]) system with heavy electron doping has been studied by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility and specific heat. The non-doped compound exhibits superconductivity at [Formula: see text] K, which is possibly due to an internal uniaxial chemical pressure that is manifested by the extremely small value of As height with respect to the Fe plane. With the oxygen substitution, the T _c value decreases rapidly to below 2 K for [Formula: see text], and surprisingly, superconductivity re-appears in the range of [Formula: see text] with a maximum [Formula: see text] of 17.5 K at x  =  0.3. For the normal-state resistivity, while the samples in intermediate non-superconducting interval exhibit Fermi liquid behavior, those in other regions show a non-Fermi-liquid behavior. The specific heat jump for the superconducting sample of x  =  0.4 is [Formula: see text], which is discussed in terms of anisotropic superconducting gap. The peculiar phase diagram in ThFeAsN_1-x O _x presents additional ingredients for understanding the superconducting mechanism in iron-based superconductors.

Crystal, magnetic, and electronic structures, and properties of new BaMnPnF (Pn = As, Sb, Bi)

New BaMnPnF (Pn = As, Sb, Bi) are synthesized by stoichiometric reaction of elements with BaF₂. They crystallize in the P4/nmm space group, with the ZrCuSiAs-type structure, as indicated by X-ray crystallography. Electrical resistivity results indicate that Pn = As, Sb, and Bi are semiconductors with band gaps of 0.73 eV, 0.48 eV and 0.003 eV (extrinsic value), respectively. Powder neutron diffraction reveals a G-type antiferromagnetic order below T_N = 338(1) K for Pn = As, and below T_N = 272(1) K for Pn = Sb. Magnetic susceptibility increases with temperature above 100 K for all the materials. Density functional calculations find semiconducting antiferromagnetic compounds with strong in-plane and weaker out-of-plane exchange coupling that may result in non-Curie Weiss behavior above T_N. The ordered magnetic moments are 3.65(5) μ_B/Mn for Pn = As, and 3.66(3) μ_B/Mn for Pn = Sb at 4 K, as refined from neutron diffraction experiments.