NaFe₃(HPO₃)₂((H,F)PO₂OH)₆: A Potential Cathode Material and a Novel Ferrimagnet

A novel iron fluorophosphite, NaFe₃(HPO₃)₂­((H,F)­PO₂OH)₆, was synthesized by a dry low-temperature synthesis route. The phase was shown to be electrochemically active for reversible insertion of Na⁺ ions, with an average discharge voltage of 2.5 V and an experimental capacity at low rates of up to 90 mAhg⁻¹. Simple synthesis, low-cost materials, excellent capacity retention, and efficiency suggest this class of material is competitive with similar oxyanion-based compounds as a cathode material for Na batteries. The characterization of physical properties by means of magnetization, specific heat, and electron spin resonance measurements confirms the presence of two magnetically nonequivalent Fe³⁺ sites. The compound orders magnetically at <i>T</i>_C ≈ 9.4 K into a state with spontaneous magnetization

Stable Sulfuric Vapor Transport and Liquid Sulfur Growth on Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) are an emergent class of low-dimensional materials with growing applications in the field of nanoelectronics. However, efficient methods for synthesizing large monocrystals of these systems are still lacking. Here, we describe an efficient synthetic route for a large number of TMDs that were obtained in quartz glass ampoules by sulfuric vapor transport and liquid sulfur. Unlike the sublimation technique, the metal enters the gas phase in the form of molecules, hence containing a greater amount of sulfur than the growing crystal. We have investigated the physical properties for a selection of these crystals and compared them to state-of-the-art findings reported in the literature. The acquired electronic properties features demonstrate the overall high quality of single crystals grown in this work as exemplified by CoS2, ReS2, NbS2, and TaS2. This new approach to synthesize high-quality TMD single crystals can alleviate many material quality concerns and is suitable for emerging electronic devices

The First Vanadate–Carbonate, K₂Mn₃(VO₄)₂(CO₃): Crystal Structure and Physical Properties

Mixed potassium–manganese vanadate–carbonate, K₂Mn₃(VO₄)₂(CO₃), represents a novel structure type; it has been synthesized hydrothermally from the system MnCl₂–K₂CO₃–V₂O₅–H₂O. Its hexagonal crystal structure was determined by single-crystal X-ray diffraction with <i>a</i> = 5.201(1) Å, <i>c</i> = 22.406(3) Å, space group <i>P</i>6₃/<i>m</i>, <i>Z</i> = 2, ρ_c = 3.371 g/cm³, and <i>R</i> = 0.022. The layered structure of the compound can be described as a combination of honeycomb-type modules of [MnO₆] octahedra and [VO₄] tetrahedra, alternating in the [001] direction with layers of [MnCO₃] built by [MnO₅] trigonal bipyramids and [CO₃] planar triangles, sharing oxygen vertices. The K⁺ ions are placed along channels of the framework, elongated in the [100], [010], and [110] directions. The title compound exhibits rich physical properties reflected in a phase transition of presumably Jahn–Teller origin at <i>T</i>₃ = 80–100 K as well as two successive magnetic phase transitions at <i>T</i>₂ = 3 K and <i>T</i>₁ = 2 K into a weakly ferromagnetic ground state, as evidenced in magnetization, specific heat, and X-band electron spin resonance measurements. A negative Weiss temperature Θ = −114 K and strongly reduced effective magnetic moment μ_eff² ∼ 70 μ_B² per formula unit suggest that antiferromagnetic exchange interactions dominate in the system. Divalent manganese is present in a high-spin state, <i>S</i> = ⁵/₂, in the octahedral environment and a low-spin state, <i>S</i> = ¹/₂, in the trigonal-bipyramidal coordination

Crystal Structure, Defects, Magnetic and Dielectric Properties of the Layered Bi_3<i>n</i>+1Ti₇Fe_{3<i>n</i>–3}O_9<i>n</i>+11 Perovskite-Anatase Intergrowths

The Bi_3<i>n</i>+1Ti₇Fe_{3<i>n</i>–3}O_9<i>n</i>+11 materials are built of (001)_p plane-parallel perovskite blocks with a thickness of <i>n</i> (Ti,Fe)­O₆ octahedra, separated by periodic translational interfaces. The interfaces are based on anatase-like chains of edge-sharing (Ti,Fe)­O₆ octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi³⁺ cations. In this work, the structure of the <i>n</i> = 4–6 Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3<i>a</i>_p periodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±<i>a</i>_p along [100]_p. The ordered arrangement of the interfaces gives rise to orthorhombic <i>Immm</i> and monoclinic <i>A</i>2/<i>m</i> polymorphs with the unit cell parameters <b>a</b> = 3<b>a</b>_p, <b>b</b> = <b>b</b>_p, <b>c</b> = 2­(<i>n</i> + 1)<b>c</b>_p and <b>a</b> = 3<b>a</b>_p, <b>b</b> = <b>b</b>_p, <b>c</b> = 2­(<i>n</i> + 1)<b>c</b>_p – <b>a</b>_p, respectively. While the <i>n</i> = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi³⁺ cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)­O₂ layers at the border of the perovskite blocks. The coupling is strong in the <i>n</i> = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the <i>n</i> = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 materials demonstrate an unusual diversity of structure defects. The <i>n</i> = 4–6 homologues are robust antiferromagnets below <i>T</i>_N = 135, 220, and 295 K, respectively. They show a high dielectric constant that weakly increases with temperature and is relatively insensitive to the Ti/Fe ratio

Synthesis and Characterization of MnCrO₄, a New Mixed-Valence Antiferromagnet

A new orthorhombic phase, MnCrO₄, isostructural with MCrO₄ (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH₄)₂Cr₂O₇ + 2 Mn­(NO₃)₂, followed by calcination at 400 °C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO₄ phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn²⁺Cr⁶⁺O₄. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at <i>T</i>_N ≈ 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above <i>T</i>_N. MnCrO₄ is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 °C to form first Cr₂O₃ plus Mn₃O₄ and then Mn_1.5Cr_1.5O₄ spinel

Crystal Structure, Defects, Magnetic and Dielectric Properties of the Layered Bi_3<i>n</i>+1Ti₇Fe_{3<i>n</i>–3}O_9<i>n</i>+11 Perovskite-Anatase Intergrowths

The Bi_3<i>n</i>+1Ti₇Fe_{3<i>n</i>–3}O_9<i>n</i>+11 materials are built of (001)_p plane-parallel perovskite blocks with a thickness of <i>n</i> (Ti,Fe)­O₆ octahedra, separated by periodic translational interfaces. The interfaces are based on anatase-like chains of edge-sharing (Ti,Fe)­O₆ octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi³⁺ cations. In this work, the structure of the <i>n</i> = 4–6 Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3<i>a</i>_p periodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±<i>a</i>_p along [100]_p. The ordered arrangement of the interfaces gives rise to orthorhombic <i>Immm</i> and monoclinic <i>A</i>2/<i>m</i> polymorphs with the unit cell parameters <b>a</b> = 3<b>a</b>_p, <b>b</b> = <b>b</b>_p, <b>c</b> = 2­(<i>n</i> + 1)<b>c</b>_p and <b>a</b> = 3<b>a</b>_p, <b>b</b> = <b>b</b>_p, <b>c</b> = 2­(<i>n</i> + 1)<b>c</b>_p – <b>a</b>_p, respectively. While the <i>n</i> = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi³⁺ cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)­O₂ layers at the border of the perovskite blocks. The coupling is strong in the <i>n</i> = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the <i>n</i> = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi_3<i>n</i>+1­Ti₇Fe_{3<i>n</i>–3}­O_9<i>n</i>+11 materials demonstrate an unusual diversity of structure defects. The <i>n</i> = 4–6 homologues are robust antiferromagnets below <i>T</i>_N = 135, 220, and 295 K, respectively. They show a high dielectric constant that weakly increases with temperature and is relatively insensitive to the Ti/Fe ratio

Synthesis and Characterization of MnCrO₄, a New Mixed-Valence Antiferromagnet

A new orthorhombic phase, MnCrO₄, isostructural with MCrO₄ (M = Mg, Co, Ni, Cu, Cd) was prepared by evaporation of an aqueous solution, (NH₄)₂Cr₂O₇ + 2 Mn­(NO₃)₂, followed by calcination at 400 °C. It is characterized by redox titration, Rietveld analysis of the X-ray diffraction pattern, Cr K edge and Mn K edge XANES, ESR, magnetic susceptibility, specific heat and resistivity measurements. In contrast to the high-pressure MnCrO₄ phase where both cations are octahedral, the new phase contains Cr in a tetrahedral environment suggesting the charge balance Mn²⁺Cr⁶⁺O₄. However, the positions of both X-ray absorption K edges, the bond lengths and the ESR data suggest the occurrence of some mixed-valence character in which the mean oxidation state of Mn is higher than 2 and that of Cr is lower than 6. Both the magnetic susceptibility and the specific heat data indicate an onset of a three-dimensional antiferromagnetic order at <i>T</i>_N ≈ 42 K, which was confirmed also by calculating the spin exchange interactions on the basis of first principles density functional calculations. Dynamic magnetic studies (ESR) corroborate this scenario and indicate appreciable short-range correlations at temperatures far above <i>T</i>_N. MnCrO₄ is a semiconductor with activation energy of 0.27 eV; it loses oxygen on heating above 400 °C to form first Cr₂O₃ plus Mn₃O₄ and then Mn_1.5Cr_1.5O₄ spinel

Multifunctional Compound Combining Conductivity and Single-Molecule Magnetism in the Same Temperature Range

We report the first highly conducting single-molecule magnet, (BEDO)₄[ReF₆]·6H₂O [<b>1</b>; BEDO = bis­(ethylenedioxo)­tetrathiafulvalene], whose conductivity and single-molecule magnetism coexist in the same temperature range. The compound was synthesized by BEDO electrocrystallization in the presence of (Ph₄P)₂[ReF₆]·2H₂O and characterized by crystallography and measurements of the conductivity and alternating-current magnetic susceptibility

Structure–Property Relationships in α‑, β′‑, and γ‑Modifications of Mn₃(PO₄)₂

The manganese orthophosphate, Mn₃(PO₄)₂, is characterized by the rich variety of polymorphous modifications, α-, β′-, and γ-phases, crystallized in monoclinic <i>P</i>2₁/<i>c</i> (<i>P</i>2₁/<i>n</i>) space group type with unit cell volume ratios of 2:6:1. The crystal structures of these phases are constituted by three-dimensional framework of corner- and edge-sharing [MnO₅] and [MnO₆] polyhedra strengthened by [PO₄] tetrahedra. All compounds experience long-range antiferromagnetic order at Neel temperature <i>T</i>_N = 21.9 K (α-phase), 12.3 K (β′-phase), and 13.3 K (γ-phase). Additionally, second magnetic phase transition takes place at <i>T</i>* = 10.3 K in β′-phase. The magnetization curves of α- and β′-modifications evidence spin-floplike features at <i>B</i> = 1.9 and 3.7 T, while the γ-Mn₃(PO₄)₂ stands out for an extended one-third magnetization plateau stabilized in the range of magnetic field <i>B</i> = 7.5–23.5 T. The first-principles calculations define the main paths of superexchange interaction between Mn spins in these polymorphs. The spin model for α-phase is found to be characterized by collection of uniform and alternating chains, which are coupled in all three directions. The strongest magnetic exchange interaction in γ-phase emphasizes the trimer units, which make chains that are in turn weakly coupled to each other. The spin model of β′-phase turns out to be more complex compared to α- or γ-phase. It shows complex chain structures involving exchange interactions between Mn2 (Mn2′, Mn2″) and Mn3 (Mn3′, Mn3″). These chains interact through exchanges involving Mn1 (Mn1′, Mn1″) spins

A₂MnXO₄ Family (A = Li, Na, Ag; X = Si, Ge): Structural and Magnetic Properties

Four new manganese germanates and silicates, A₂MnGeO₄ (A = Li, Na) and A₂MnSiO₄ (A = Na, Ag), were prepared, and their crystal structures were determined using the X-ray Rietveld method. All of them contain all components in tetrahedral coordination. Li₂MnGeO₄ is orthorhombic (<i>Pmn</i>2₁) layered, isostructural with Li₂CdGeO₄, and the three other compounds are monoclinic (<i>Pn</i>) cristobalite-related frameworks. As in other stuffed cristobalites of various symmetry (<i>Pn</i> A₂MXO₄, <i>Pna</i>2₁ and <i>Pbca</i> AMO₂), average bond angles on bridging oxygens (here, Mn–O–X) increase with increasing A/X and/or A/M radius ratios, indicating the trend to the ideal cubic (<i>Fd</i>3̅<i>m</i>) structure typified by CsAlO₂. The sublattices of the magnetic Mn²⁺ ions in both structure types under study (<i>Pmn</i>2₁ and <i>Pn</i>) are essentially the same; namely, they are pseudocubic eutaxy with 12 nearest neighbors. The magnetic properties of the four new phases plus Li₂MnSiO₄ were characterized by carrying out magnetic susceptibility, specific heat, magnetization, and electron spin resonance measurements and also by performing energy-mapping analysis to evaluate their spin exchange constants. Ag₂MnSiO₄ remains paramagnetic down to 2 K, but A₂MnXO₄ (A = Li, Na; X = Si, Ge) undergo a three-dimensional antiferromagnetic ordering. All five phases exhibit short-range AFM ordering correlations, hence showing them to be low-dimensional magnets and a magnetic field induced spin-reorientation transition at <i>T</i> < <i>T</i>_N for all AFM phases. We constructed the magnetic phase diagrams for A₂MnXO₄ (A = Li, Na; X = Si, Ge) on the basis of the thermodynamic data in magnetic fields up to 9 T. The magnetic properties of all five phases experimentally determined are well explained by their spin exchange constants evaluated by performing energy-mapping analysis