Assembling the Puzzle of Coparsite Polymorphism: Synthesis, Thermal Expansion, and Quantum Magnetism of α- and β-CuO(VO)Cl.

Two new dimorphic spin-1/2 quantum magnets, α- and β-CuO(VO)Cl, were synthesized via a chemical vapor transport method that emulates mineral formation in volcanic fumaroles. α-CuO(VO)Cl () is a pure vanadate analogue of the coparsite mineral characterized by [OCu] 1 single rods, whereas β-CuO(VO)Cl () adopts a new structure type with the [OCu] 2 layered topology. The thermal expansions of both and studied by high-temperature single-crystal X-ray diffraction are reported.

Kitaev interactions through extended superexchange pathways in the Ru honeycomb magnet RuPSiO.

Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement.

Intriguing Low-Temperature Phase in the Antiferromagnetic Kagome Metal FeGe.

The properties of kagome metals are governed by the interdependence of band topology and electronic correlations resulting in remarkably rich phase diagrams. Here, we study the temperature evolution of the bulk electronic structure of the antiferromagnetic kagome metal FeGe using infrared spectroscopy. We uncover drastic changes in the low-energy interband absorption at the 100 K structural phase transition that has been linked to a charge-density-wave (CDW) instability.

CoVO High-Pressure Polymorphs: To Order or Not to Order?

Materials properties are determined by their compositions and structures. In ABO oxides different cation orderings lead to mainly perovskite- or corundum like derivatives with exciting physical properties. Sometimes, a material can be stabilized in more than one structural modification, providing a unique opportunity to explore structure-properties relationship.

(CNH)[FeFe(SO)(HO)]: A Framework Iron Sulfate with a Mixed = 2 and = 5/2 Honeycomb Lattice.

A new guanidinium-templated hydrated iron sulfate, [CNH][FeFe(SO)(HO)] (), was prepared from strongly acidic aqueous solutions. Its crystal structure is comprised from FeO and FeO(HO) octahedra linked by sulfate bridges forming a [FeFe(SO)(HO)] 3 framework with a layer-by-layer ordering of ferric and ferrous cations. The structural topology of the framework is related to the anhydrous rhombohedral mikasaite Fe(SO).

Effect of antifluorite layer on the magnetic order in Eu-based 1111 compounds, EuTAsF (T = Zn, Mn, and Fe).

The 1111 compounds with an alternating sequence of fluorite and antifluorite layers serve as structural hosts for the vast family of Fe-based superconductors. Here, we use neutron powder diffraction and density-functional-theory (DFT) band-structure calculations to study magnetic order of Eu in the [EuF] fluorite layers depending on the nature of the [TAs] antifluorite layer that can be non-magnetic semiconducting (T = Zn), magnetic semiconducting (T = Mn), or magnetic metallic (T = Fe). Antiferromagnetic transitions at ∼ 2.

Chemical Vapor Transport Synthesis of Cu(VO)(AsO) With Two Distinct Spin-1/2 Magnetic Ions.

A new copper vanadyl arsenate, Cu(VO)(AsO), was synthesized via the chemical vapor transport method. Cu(VO)(AsO) adopts an original structure type. It is characterized by layers formed by edge-sharing and corner-sharing V-centered octahedra resulting in a unique topology that was hitherto not reported for vanadates.

Composition dependent polymorphism and superconductivity in Y{Rh,Ir}Ge.

Polymorphism is observed in the YRhGe series. The decrease of Y-content leads to the transformation of the primitive cubic YRhGe [ = 0.6, space group 3̄, = 8.

Semiconducting and Metallic Compounds within the IrIn Structure Type: Stability and Chemical Bonding.

Narrow-gap semiconductors are very rare among intermetallic compounds. They appear only when two factors come together: strong hybridization of valence orbitals in the vicinity of the Fermi level and an appropriate number of valence electrons. Surprisingly, the IrIn family of intermetallics contains a number of semiconductors, including 17 e FeGa, RuGa, OsGa, and RuIn, for which the d-p hybridization gap opens at the Fermi energy.

Hybrid electrons in the trimerized GaVO.

Mixed-valent transition-metal compounds display complex structural, electronic and magnetic properties, which often intricately coexist. Here, we report the new ternary oxide GaVO, a structural sibling of skyrmion-hosting lacunar spinels. GaVO contains a vanadium trimer and an original spin-orbital-charge texture that forms upon the structural phase transition at T = 68 K followed by the magnetic transition at T = 35 K.

Entropic Balance Conditions and Optimization of Distillation Column System.

The paper considers the limitation problem of the distillation column systems separating multicomponent mixtures with serial and parallel structures. The solution takes into account the irreversibility of processes. Using entropic balance conditions, the dependence of load on heat consumption is obtained for a binary distillation column.

From ( = 1) Spin Hexamer to Spin Tetradecamer by CuO Interstitials in ACuO(CuO)(SO) (A = alkali).

(Na,K)CuO(SO) compounds form structural chains of Cu hexameric units with nominal = 1 spins due to the interplay between inner strong antiferromagnetic and ferromagnetic exchanges. We show here that the lattice relaxation after the replacement of alkali by larger Rb and Cs ones is accompanied by the insertion of neutral CuO species into (Rb,Cs)CuO(CuO)(SO) phases. Structurally, interstitial CuO links the next two Cu units in longer Cu tetradecameric ones.

Structural Stability and Properties of Marokite-Type γ-MnO.

We synthesized single crystals of marokite (CaMnO)-type orthorhombic manganese (II,III) oxide, γ-MnO, in a multianvil apparatus at pressures of 10-24 GPa. The magnetic, electronic, and optical properties of the crystals were investigated at ambient pressure. It was found that γ-MnO is a semiconductor with an indirect band gap of 0.

Synthesis of Ilmenite-type ε-MnO and Its Properties.

In contrast to the corundum-type AX structure, which has only one crystallographic site available for trivalent cations (e.g., in hematite), the closely related ABX ilmenite-type structure comprises two different octahedrally coordinated positions that are usually filled with differently charged ions (e.

Cooperative Cluster Jahn-Teller Effect as a Possible Route to Antiferroelectricity.

We report the observation of an antipolar phase in cubic GaNb_{4}S_{8} driven by an unconventional microscopic mechanism, the cooperative Jahn-Teller effect of Nb_{4}S_{4} molecular clusters. The assignment of the antipolar nature is based on sudden changes in the crystal structure and a strong drop of the dielectric constant at T_{JT}=31  K, also indicating the first-order nature of the transition. In addition, we found that local symmetry lowering precedes long-range orbital ordering, implying the presence of a dynamic Jahn-Teller effect in the cubic phase above T_{JT}.

Magnetic structures of FeGeAs and FeGeP intermetallic compounds: a neutron diffraction and Fe Mössbauer spectroscopy study.

FeGeAs and FeGeP are quasi-binary intermetallic compounds that possess a rare variant of intergrowth-type crystal structure, which is a combination of the column shaped CoAl and MgFeGe structure type blocks. The compounds are antiferromagnets with the Néel temperatures around 125 K. Neutron powder diffraction experiments on the samples with δ≈ 0.

Averaged Optimization and Finite-Time Thermodynamics.

The paper considers typical extremum problems that contain mean values of control variables or some functions of these variables. Relationships between such problems and cyclic modes of dynamical systems are explained and optimality conditions for these modes are found. The paper shows how these problems are linked to the field of finite-time thermodynamics.

Finite-Time Thermodynamics in Economics.

In this paper, we consider optimal trading processes in economic systems. The analysis is based on accounting for irreversibility factors using the wealth function concept. The existence of the welfare function is proved, the concept of capital dissipation is introduced as a measure of the irreversibility of processes in the microeconomic system, and the economic balances are recorded, including capital dissipation.

Crystal structure, phase transition and properties of indium(III) sulfide.

Poly- and single-crystalline samples of In0.67□0.33In2S4 thiospinel were obtained by various powder metallurgical and chemical vapor transport methods, respectively.

Thermodynamic Perspective on Field-Induced Behavior of α-RuCl_{3}.

Measurements of the magnetic Grüneisen parameter (Γ_{B}) and specific heat on the Kitaev material candidate α-RuCl_{3} are used to access in-plane field and temperature dependence of the entropy up to 12 T and down to 1 K. No signatures corresponding to phase transitions are detected beyond the boundary of the magnetically ordered region, but only a shoulderlike anomaly in Γ_{B}, involving an entropy increment as small as 10^{-5}Rlog2. These observations put into question the presence of a phase transition between the purported quantum spin liquid and the field-polarized state of α-RuCl_{3}.

Li(SeO)(HO)·CuCl, a salt-inclusion diselenite structurally based on tetranuclear Li complexes.

A new lithium copper diselenite chloride hydrate, LiSeO(HO)·CuCl, was prepared from aqueous solution. Its unique 2D structure can be interpreted as LiSeO(HO) layers with CuCl hosts embedded in the interlayer space, and be considered halfway between the salt-inclusion and host-guest structures. The CuOCl octahedra form chains similar to those in CuCl·2HO, yet water molecules are coordinated exclusively to Li while SeO and Cl bridge Li and Cu.

Synthesis, electronic structure and physical properties of two new layered compounds, EuFAgSe and EuFAgTe, featuring the active redox pair Eu/Ag.

Systematic studies of the ZrCuSiAs (also LaOAgS or 1111) structure type resulted in the synthesis of two new fluoride chalcogenides, EuFAgSe and EuFAg1-δTe, whereas their sulfide analog, EuFAgS, could not be obtained. Both new compounds are tetragonal, P4/nmm, with cell parameters a = 4.1542(1) Å, c = 9.

Two Linear Regimes in Optical Conductivity of a Type-I Weyl Semimetal: The Case of Elemental Tellurium.

Employing high-pressure infrared spectroscopy we unveil the Weyl semimetal phase of elemental Te and its topological properties. The linear frequency dependence of the optical conductivity provides clear evidence for metallization of trigonal tellurium (Te-I) and the linear band dispersion above 3.0 GPa.

Spin liquids in geometrically perfect triangular antiferromagnets.

The cradle of quantum spin liquids, triangular antiferromagnets show strong proclivity to magnetic order and require deliberate tuning to stabilize a spin-liquid state. In this brief review, we juxtapose recent theoretical developments that trace the parameter regime of the spin-liquid phase, with experimental results for Co-based and Yb-based triangular antiferromagnets. Unconventional spin dynamics arising from both ordered and disordered ground states are discussed, and the notion of a geometrically perfect triangular system is scrutinized to demonstrate non-trivial imperfections that may assist magnetic frustration in stabilizing dynamic spin states with peculiar excitations.