Chains Of Octahedra Research Articles

A new cadmium rare-earth oxyborate Cd4DyO(BO3)3 and luminescent properties of the Cd4Dy1-xSmxO(BO3)3 (0 ≤ x ≤ 0.8) phosphors

A new cadmium-rare earth (Dy) oxyborate Cd4DyO(BO3)3 has been prepared by a high-temperature solution reaction at 950 ​°C. The compound crystallizes in the space group Cm with a ​= ​7.9549(2) Å, b ​= ​15.7792(3) Å, c ​= ​3.4738(1) Å, β ​= 100.183(2)°, V ​= ​429.166(17) Å3, and Z ​= ​2. Its crystal structure consists of 1D [DyO4]n5n− chains of edge-sharing DyO6 octahedra and 1D [Cd2O6]n8n− double chains formed by corner- or edge-sharing CdO5 and CdO6 polyhedra. These chains are held together via common O atoms leading to a 3D [Cd4DyO10]n9n− network, with B atoms residing in channels of the network to balance charge, thus the final 3D network of Cd4DyO(BO3)3 is formed. IR and Raman studies support the presence of BO3 groups in the structure. Solid solutions of Cd4Dy1-xSmxO(BO3)3 (0 ​≤ ​x ​≤ ​0.8) were prepared via solid-state reaction method and their photoluminescence properties were studied. It was found that under near-UV excitation, the luminescence color of Cd4Dy1-xSmxO(BO3)3 fluorescent powders can be tuned from yellowish white through white to purplish white by rationally controlling the Sm3+/Dy3+ concentration ratio. The Cd4Dy0.8Sm0.2O(BO3)3 phosphor excited at 364 ​nm has CIE coordinates (0.338,0.328) and a CCT value of 5240 ​K, which indicates that it has the potential to be used as a single-component white-emitting phosphor for commercial W-LEDs. Moreover, XPS and UV–vis absorption spectra of Cd4DyO(BO3)3 have also been investigated.

High-Pressure Synthesis of Rare-Earth Borate-Nitrate Crystals for Second Harmonic Generation.

The crystals of a novel family of rare-earth borate-nitrate compounds, Ln7(BO3)3(NO3)N3O (Ln = Pr, Nd), were grown at high-pressure in KAs flux and their crystal structure was determined. The new type of the crystalline structure consists of parallel chains of Ln6 octahedra connected by common faces and forming the channels with the NO3 triangular planar motifs in the center, and isolated OLn4 tetrahedra separated from each other by N3 triangular motifs. Each NO3 triangle is in fact a part of rather unusual (NB3O12) block consisting of 3 distorted BO4 tetrahedra around central nitrogen atom. Under near-infrared (NIR) (λex = 1064 nm) excitation, both compounds revealed a strong signal of second harmonic generation (SHG) at half the excitation wavelength (λem = 532 nm), which is in agreement with their noncentrosymmetric structure. In addition, a photon up-conversion (UC) emission at λem = 880 nm was observed for microcrystals of Nd7(BO3)3(NO3)N3O, which was assigned to the UC process occurring within the 4f electronic manifold of Nd3+ ions. The dual-emission (SHG/UC) properties of Nd7(BO3)3(NO3)N3O microcrystals, concomitant with the absence of photobleaching, makes them prospective candidates for microscopic probes in biological studies.

Rippite, K2(Nb,Ti)2(Si4O12)O(O,F), a New K-Nb-Cyclosilicate from Chuktukon Carbonatite Massif, Chadobets Upland, Krasnoyarsk Territory, Russia

Rippite K2(Nb,Ti)2(Si4O12)(O,F)2, a new K-Nb-cyclosilicate, has been discovered in calciocarbonatites from the Chuktukon massif (Chadobets upland, SW Siberian Platform, Krasnoyarsk Territory, Russia). It was found in a primary mineral assemblage, which also includes calcite, fluorcalciopyrochlore, tainiolite, fluorapatite, fluorite, Nb-rich rutile, olekminskite, K-feldspar, Fe-Mn–dolomite and quartz. Goethite, francolite (Sr-rich carbonate–fluorapatite) and psilomelane (romanèchite ± hollandite) aggregates as well as barite, monazite-(Ce), parisite-(Ce), synchysite-(Ce) and Sr-Ba-Pb-rich keno-/hydropyrochlore are related to a stage of metasomatic (hydrothermal) alteration of carbonatites. The calcite–dolomite coexistence assumes crystallization temperature near 837 °C for the primary carbonatite paragenesis. Rippite is tetragonal: P4bm, a = 8.73885(16), c = 8.1277(2) Å, V = 620.69(2) Å3, Z = 2. It is closely identical in the structure and cell parameters to synthetic K2Nb2(Si4O12)O2 (or KNbSi2O7). Similar to synthetic phase, the mineral has nonlinear properties. Some optical and physical properties for rippite are: colorless; Mohs’ hardness—4–5; cleavage—(001) very perfect, (100) perfect to distinct; density (meas.)—3.17(2) g/cm3; density (calc.)—3.198 g/cm3; optically uniaxial (+); ω = 1.737-1.739; ε = 1.747 (589 nm). The empirical formula of the holotype rippite (mean of 120 analyses) is K2(Nb1.90Ti0.09Zr0.01)[Si4O12](O1.78OH0.12F0.10). Majority of rippite prismatic crystals are weakly zoned and show Ti-poor composition K2(Nb1.93Ti0.05Zr0.02)[Si4O12](O1.93F0.07). Raman and IR spectroscopy, and SIMS data indicate very low H2O content (0.09–0.23 wt %). Some grains may contain an outermost zone, which is enriched in Ti (+Zr) and F, up to K2(Nb1.67Ti0.32Zr0.01)[Si4O12](O1.67F0.33). It strongly suggests the incorporation of (Ti,Zr) and F in the structure of rippite via the isomorphism Nb5+ + O2− → (Ti,Zr)4+ + F1−. The content of a hypothetical end-member K2Ti2[Si4O12]F2 may be up to 17 mol. %. Rippite represents a new structural type among [Si4O12]-cyclosilicates because of specific type of connection of the octahedral chains and [Si4O12]8− rings. In structural and chemical aspects it seems to be in close with the labuntsovite-supergroup minerals, namely with vuoriyarvite-(K), K2(Nb,Ti)2(Si4O12)(O,OH)2∙4H2O.

Galeaclolusite, [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O, a new bulachite-related mineral from Cap Garonne, France

AbstractGaleaclolusite, [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O, is a new secondary hydrated aluminium arsenate mineral from Cap Garonne, Var, France. It forms crusts and spheroids of white fibres up to 50 μm long by 0.4 μm wide and only 0.1 μm thick. The fibres are elongated along [001] and flattened on (100). The calculated density is 2.27 g⋅cm–3. Optically, galeaclolusite is biaxial with α = 1.550(5), β not determined, γ = 1.570(5) (white light) and partial orientation: Z = c (fibre axis). Electron microprobe analyses coupled with crystal structure refinement results gives an empirical formula based on 33 O atoms of Al5.72Si0.08As2.88O33H34.12. Galeaclolusite is orthorhombic, Pnma, with a = 19.855(4), b = 17.6933(11), c = 7.7799(5) Å, V = 2733.0(7) Å3 and Z = 4. The crystal structure of galeaclolusite was established from its close relationship to bulachite and refined using synchrotron powder X-ray diffraction data. It is based on heteropolyhedral layers, parallel to (100), of composition Al6(AsO4)3(OH)9(H2O)4 and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner-connected AsO4 tetrahedra, that are the same as in the mineral liskeardite.

Investigation of bipartite entanglement across the magnetization process of a highly frustrated spin-1/2 Heisenberg octahedral chain as a new paradigm of the localized-magnon approach

The bipartite entanglement across the magnetization process of a highly frustrated spin-1/2 Heisenberg octahedral chain is examined within the concept of localized magnons, which enables a simple calculation of the concurrence measuring a strength of the pairwise entanglement between nearest-neighbor and next-nearest-neighbor spins from square plaquettes. A full exact diagonalization of the finite-size Heisenberg octahedral chain with up to 4 unit cells (20 spins) evidences an extraordinary high precision of the localized-magnon theory in predicting measures of the bipartite entanglement at sufficiently low temperatures. While the monomer-tetramer phase emergent at low enough magnetic fields exhibits presence (absence) of the bipartite entanglement between the nearest-neighbor (next-nearest-neighbor) spins, the magnon-crystal phase emergent below the saturation field contrarily displays identical bipartite entanglement between the nearest-neighbor and next-nearest-neighbor spins. The presented results verify a new paradigm of the localized-magnon approach concerned with a simple calculation of entanglement measures.

Crystal structure and temperature-dependent properties of Na2H4Ga2GeO8 – a novel gallogermanate

Abstract Synthesis, crystal structure and temperature-dependent behavior of Na2H4Ga2GeO8 are reported. This novel gallogermanate crystallizes in space group I41/acd with room-temperature powder diffraction lattice parameters of a = 1298.05(1) pm and c = 870.66(1) pm. The structure consists of MO4 (M = Ga, Ge) tetrahedra in four-ring chains, which are connected by two different (left- and right-handed) helical chains of NaO6 octahedra. Protons coordinating the oxygen atoms of the GaO4 tetrahedra not linked to germanium atoms ensure the charge balance. Structure solution and refinement are based on single crystal X-ray diffraction measurements. Proton positions are estimated using a combined approach of DFT calculations and NMR, FTIR and Raman spectroscopic techniques. The thermal expansion was examined in the range between T = 20(2) K and the compound’s decomposition temperature at 568(5) K, in which no phase transition could be observed, and Debye temperatures of 266(11) and 1566(65) K were determined for the volume expansion.

Rüdlingerite, Mn2+2V5+As5+O7·2H2O, a New Species Isostructural with Fianelite

The new mineral species rüdlingerite, ideally Mn2+2V5+As5+O7·2H2O, occurs in the Fianel mine, in Val Ferrera, Grisons, Switzerland, a small Alpine metamorphic Mn deposit. It is associated with ansermetite and Fe oxyhydroxide in thin fractures in Triassic dolomitic marbles. Rüdlingerite was also found in specimens recovered from the dump of the Valletta mine, Canosio, Cuneo, Piedmont, Italy, where it occurs together with massive braccoite and several other As- and V-rich phases in richly mineralized veins crossing the quartz-hematite ore. The new mineral displays at both localities yellow to orange, flattened elongated prismatic, euhedral crystals measuring up to 300 μm in length. Electron-microprobe analysis of rüdlingerite from Fianel gave (in wt%): MnO 36.84, FeO 0.06, As2O5, 25.32, V2O5 28.05, SiO2 0.13, H2Ocalc 9.51, total 99.91. On the basis of 9 O anions per formula unit, the chemical formula of rüdlingerite is Mn1.97(V5+1.17 As0.83Si0.01)Σ2.01O7·2H2O. The main diffraction lines are [dobs in Å (Iobs) hkl]: 3.048 (100) 022, 5.34 (80) 120, 2.730 (60) 231, 2.206 (60) 16-1, 7.28 (50) 020, 2.344 (50) 250, 6.88 (40) 110, and 2.452 (40) 320. Study of the crystal structure showcases a monoclinic unit cell, space group P21/n, with a = 7.8289(2) Å, b = 14.5673(4) Å, c = 6.7011(2) Å, β = 93.773(2)°, V = 762.58(4) Å3, Z = 4. The crystal structure has been solved and refined to R1 = 0.041 on the basis of 3784 reflections with Fo > 4σ(F). It shows Mn2+ hosted in chains of octahedra that are subparallel to [-101] and bound together by pairs of tetrahedra hosted by V5+ and As5+, building up a framework. Additional linkage is provided by hydrogen-bonding through H2O coordinating Mn2+ at the octahedra. One tetrahedrally coordinated site is dominated by V5+, T(1)(V0.88As0.12), corresponding to an observed site scattering of 24.20 electrons per site (eps), whereas the second site is strongly dominated by As5+,T(2)(As0.74V0.26), with, accordingly, a higher observed site scattering of 30.40 eps. The new mineral has been approved by the IMA-CNMNC and named for Gottfried Rüdlinger (born 1919), a pioneer in the 1960–1980s, in the search and study of the small minerals from the Alpine manganese mineral deposits of Grisons.

Structural Variations in Manganese Halide Chain Compounds Mediated by Methylimidazolium Isomers

The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl3(H2O) and [4MiH]MnCl3(H2O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl3(H2O)]n− edge-sharing octahedral chains. The structures are compared to the previously reported isomeric analogue [2MiH]MnCl3(H2O) ([2MiH] = 2-methylimidazolium), and three closely related compounds. The variations in packing of the inorganic chains are shown to be influenced by hydrogen bonding abilities of the imidazolium or related moieties. Both new compounds show intense red luminescence at ambient temperature under UV irradiation.

Structural characterisation of magnesium (sodium) aluminium silicate hydrate (M-(N)-A-S-H) phases by X-ray absorption near-edge spectroscopy

Magnesium silicate hydrate phases (M-S-H) have been observed forming in low pH cements, which came in contact with Mg-rich ground waters or argillaceous rock formations, such as Opalinus Clay. Their crystallographic structure has been suggested to be a purely ordered sheet-like phyllosilicate with a tetrahedral octahedral (TOT O) layering, i.e. similarly to a talc plus brucite structure. In nature, Mg phyllosilicates with this type of layering contain several type of cations, in particular Al, as well as alkaline earth metals. This study shows that the X-ray near-edge spectra of synthesised Mg-Al- silicate hydrates and Mg-Al-Na silicate hydrates (M-A-S-H and M-N-A-S-H) show distinct differences to M-S-H, indicating the possible accommodation of Al in their structure. This is further supported by the great similarity of the spectra to natural Mg–Al containing phyllosilicates, i.e. clinochlore, having a TOT O layering. The results, furthermore, suggest that Na is not taken up in the structure due to the strong similarities of the M-N-A-S-H with the M-A-S-H phases. The comparison of the latter spectra with natural references show high resemblance not only with clinochlore, but also with sepiolite, a Mg containing phyllosilicate with water molecules bridging between broken octahedral chains. It is, therefore, suggested that the Mg in the M-(N)-A-S-H phases is bound similarly to clinochlore with a TOT O layering and that water molecules or OH groups are present between broken octahedral layers. Aluminium is possibly accommodated in the tetrahedral and/or octahedral layers.

Synthesis, crystal structure determination of a novel phosphate Ag1.64Zn1.64Fe1.36(PO4)3 with an alluaudite-like structure.

Single crystals of Ag1.64Zn1.64Fe1.36(PO4)3 [silver zinc iron phosphate (1.64/1.64/1.36/3)] have been synthesized by a conventional solid-state reaction and structurally characterized by single-crystal X-ray diffraction. The title compound crystallizes with an alluaudite-like structure. All atoms of the structure are in general positions except for four, which reside on special positions of the space group, C2/c. The Ag+ cations reside at full occupancy on inversion centre sites and at partial occupancy (64%) on a twofold rotation axis. In this structure, the unique Fe3+ ion with one of the two Zn2+ cations are substitutionally disordered on the same general position (Wyckoff site 8f), with a respective ratio of 0.68/0.32 (occupancies were fixed so as to ensure electrical neutrality for the whole structure). The remaining O and P atoms are located in general positions. The three-dimensional framework of this structure consists of kinked chains of edge-sharing octa-hedra stacked parallel to [10]. These chains are built up by a succession of [MO6] (M = Zn/Fe or Zn) units. Adjacent chains are connected by the PO4 anions, forming sheets oriented perpendicular to [010]. These inter-connected sheets generate two types of channels parallel to the c axis, in which the Ag+ cations are located. The validity and adequacy of the proposed structural model of Ag1.64Zn1.64Fe1.36(PO4)3 was established by means of bond-valence-sum (BVS) and charge-distribution (CHARDI) analysis tools.

Frustrated quantum Heisenberg double-tetrahedral and octahedral chains at high magnetic fields

We consider the spin-1/2 antiferromagnetic Heisenberg model on two one-dimensional frustrated lattices, double-tetrahedral chain and octahedral chain, with almost dispersionless (flat) lowest magnon band in a strong magnetic field. Using the localized magnons picture, we construct an effective description of the one-dimensional chains with triangle and square traps within the strong coupling approximation. We perform extensive exact diagonalization and density matrix renormalization group calculations to check the validity of the obtained effective Hamiltonians by comparison with the initial models with special focus on the magnetization and specific heat at high magnetic fields.

Jasonsmithite, a new phosphate mineral with a complex microporous framework, from the Foote mine, North Carolina, U.S.A

Abstract Jasonsmithite (IMA2019-121), Mn42+ZnAl(PO4)4(OH)(H2O)7·3.5H2O, is a pegmatite-phosphate mineral from the Foote Lithium Company mine, Kings Mountain district, Cleveland County, North Carolina, U.S.A. It is interpreted as having formed by late-stage, low-temperature hydrothermal alteration. Crystals are colorless to light brown, slightly flattened prisms to about 1 mm in length with wedge-shaped terminations. The mineral is transparent with vitreous luster, white streak, Mohs hardness 2, brittle tenacity, irregular fracture, and perfect {001} cleavage. The density is 2.63(2) g/cm3. Jasonsmithite is biaxial (–), with α = 1.561(2), β = 1.580(2), γ = 1.581(2), measured in white light. The 2V is 25(5)° and dispersion is r < ν moderate. The optical orientation is Y = b, X ^ c = 18° in obtuse β. The Raman spectrum is dominated by vibrational modes of PO4 and ZnO4 tetrahedra, AlO6 and MnO6 octahedra, and OH groups. Electron microprobe analyses gave the empirical formula (Mn3.09Fe0.87)Σ3.96Zn1.05Al0.98(PO4)4(OH)(H2O)7·3.5H2O. The mineral is monoclinic, P21/c, a = 8.5822(3), b = 13.1770(6), c = 20.3040(14) Å, β = 98.485(7)°, V = 2271.0(2) Å3, and Z = 4. The structure (R1 = 0.0443 for 3685 I>2σI reflections) contains zigzag chains of edge-sharing MnO6 octahedra that corner-link to adjacent chains and to PO4 tetrahedra to form sheets, which are decorated by ZnO4 tetrahedra. The sheets are linked to one another via dimers of AlO6 octahedra, forming a framework with large channels containing H2O groups. With H2O groups removed, the framework has a void space of 70.2% per unit cell, and a framework density of 14.5 polyhedral atoms/1000 Å3, which would place jasonsmithite among the most porous minerals.

Structure and magnetic properties of LiMVO4 (M = Mn, Cu)

LiM2+VO4 compounds with spinel-related structures show interesting electrochemical, magnetic and multiferroic properties. Neutron powder diffraction data for LiMVO4 (M ​= ​Cu, Mn) were collected at room temperature and 1.5 ​K. In contrast to single crystal NPD results, no evidence of magnetic ordering was detected for LiCuVO4 at 1.5 ​K due to the incommensurate order and low Cu2+magnetic moment. For LiMnVO4 (space group Cmcm) a clear ordered magnetic state was determined for the first time: the chains of edge-shared MnO6 octahedra have antiferromagnetic (AFM) order within each chain, and also between chains to give C′ centring. The magnetic behaviour of the MnO6 chain can be well described by the classical one-dimensional Heisenberg model with an intra-chain exchange energy of J/k ​= ​−4.32 ​K. It is believed that direct dxy ​− ​dxy AFM interactions are dominant over 90° Mn–O–Mn exchange for determining the magnetic order.

Crystal structure and characterization of magnesium carbonate chloride heptahydrate.

MgCO3·MgCl2·7H2O is the only known neutral magnesium carbonate containing chloride ions at ambient conditions. According to the literature, only small and twinned crystals of this double salt could be synthesised in a concentrated solution of MgCl2. For the crystal structure solution, single-crystal diffraction was carried out at a synchrotron radiation source. The monoclinic crystal structure (space group Cc) exhibits double chains of MgO octahedra linked by corners, connected by carbonate units and water molecules. The chloride ions are positioned between these double chains parallel to the (100) plane. Dry MgCO3·MgCl2·7H2O decomposes in the air to chlorartinite, Mg2(OH)Cl(CO3)·nH2O (n = 2 or 3). This work includes an extensive characterization of the title compound by powder X-ray diffraction, thermal analysis, SEM and vibrational spectroscopy.

Original Network of Zigzag Chains in the β Polymorph of Fe2WO6: Crystal Structure and Magnetic Ordering.

The structural and physical properties of the β polymorph of iron tungstate Fe2WO6 have been investigated by synchrotron and neutron diffraction vs temperature, combined with magnetization and dielectric properties measurements. The monoclinic P21/a crystal structure of β-Fe2WO6 has been determined and consists of an original network of zigzag chains of FeO6 and WO6 octahedra sharing trans and skew edges, connected through corners into a 3D structure. Magnetization measurements indicate an antiferromagnetic transition at TN = 264 K, which corresponds to a ↑↑↓↓ nearly collinear ordering of iron moments inside sequences of four edge-sharing FeO6 octahedra, as determined by neutron diffraction. A canting of the moments out of the ac plane is observed below 150 K, leading to a noncollinear antiferromagnetic structure, the P21/a' magnetic space group remaining unchanged. These results are discussed in comparison with the crystal and magnetic structures of γ-Fe2WO6 and with the magnetic couplings in other iron tungstates and trirutile Fe2TeO6.

Bulachite, [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O from Cap Garonne, France: Crystal structure and formation from a higher hydrate

AbstractBulachite specimens from Cap Garonne, France, comprise two intimately mixed hydrated aluminium arsenate minerals with the same Al:As ratio of 2:1 and with different water contents. The crystal structures of both minerals have been solved using data from low-dose electron diffraction tomography combined with synchrotron powder X-ray diffraction. One of the minerals has the same powder X-ray diffraction pattern (PXRD) as for published bulachite. It has orthorhombic symmetry, space group Pnma with unit-cell parameters a = 15.3994(3), b = 17.6598(3), c = 7.8083(1) Å and Z = 4, with the formula [Al6(AsO4)3(OH)9(H2O)4]⋅2H2O. The second mineral is a higher hydrate with composition [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O. It has the same Pnma space group and unit-cell parameters a = 19.855(4), b = 17.6933(11) and c = 7.7799(5) Å i.e. almost the same b and c parameters but a much larger a parameter. The structures are based on polyhedral layers, parallel to (100), of composition [Al6(AsO4)3(OH)9(H2O)4] and with H-bonded H2O between the layers. The layers contain [001] spiral chains of edge-shared octahedra, decorated with corner connected AsO4 tetrahedra that are the same as in the mineral liskeardite. The spiral chains are joined together by octahedral edge-sharing to form layers parallel to (100). Synchrotron PXRD patterns collected at different temperatures during heating of the specimen show that the higher-hydrate mineral starts transforming to bulachite when heated to 50°C, and the transformation is complete between 75 and 100°C.

Tunable Color Temperatures and Emission Enhancement in 1D Halide Perovskites under High Pressure

AbstractDesigning low‐dimensional halide perovskites (LDHPs) for broadband emissions with enhanced emission and preferred chromaticity coordinator or color temperature remains a pressing challenge. Herein, a comprehensive study is conducted about the relationship between the crystal structure and broadband emission properties of 1D halide perovskite C4N2H14PbBr4, one of promising white‐emission LDHPs. It is found that the zigzag distortion degree tuned by pressure not only suppresses the general photoluminescence quenching, but also effectively adjusts the chromaticity coordinator and color temperature of C4N2H14PbBr4 nanocrystals (NCs). The initially broad white emissive C4N2H14PbBr4 NCs can be continuously modulated to a very bright bluish‐white emission with high color‐rendering index of 86, accompanied by a significant emission enhancement. The underlying mechanism of thus pressure‐induced emission enhancement (PIEE) can be attributed to the strengthening of electron–phonon interactions of compressed C4N2H14PbBr4 NCs. Furthermore, the zigzag distortion of [PbBr42−]∞ octahedral chains is able to rearrange the depths of multiple self‐trapped states, which is also corroborated by the wavelength‐dependent decay times under pressure, ultimately giving rise to adjustable emission chromaticity. This study offers a deep insight into the relationship between PIEE and distortion degree of LDHPs at extremes and facilitates the design of new materials with the desired emission properties.

Magnetic Structure and Metamagnetic Transitions in the van der Waals Antiferromagnet CrPS4.

In 2D magnets, interlayer exchange coupling is generally weak due to the van der Waals layered structure but it still plays a vital role in stabilizing the long-range magnetic ordering and determining the magnetic properties. Using complementary neutron diffraction, magnetic, and torque measurements, the complete magnetic phase diagram of CrPS4 crystals is determined. CrPS4 shows an antiferromagnetic ground state (A-type) formed by out-of-plane ferromagnetic monolayers with interlayer antiferromagnetic coupling along the c axis below TN = 38 K. Due to small magnetic anisotropy energy and weak interlayer coupling, the low-field metamagnetic transitions in CrPS4, that is, a spin-flop transition at ≈0.7 T and a spin-flip transition from antiferromagnetic to ferromagnetic under a relatively low field of 8 T, can be realized for H∥c. Intriguingly, with an inherent in-plane lattice anisotropy, spin-flop-induced moment realignment in CrPS4 for H∥c is parallel to the quasi-1D chains of CrS6 octahedra. The peculiar metamagnetic transitions and in-plane anisotropy make few-layer CrPS4 flakes a fascinating platform for studying 2D magnetism and for exploring prototype device applications in spintronics and optoelectronics.

High-pressure synthesis, crystal structure and physical properties of a new Cr-based arsenide La3CrAs5

In La-Cr-As system, the first ternary compound La3CrAs5 has been successfully synthesized under high- pressure and high-temperature conditions. La3CrAs5 crystallizes into a hexagonal Hf5Sn3Cu-anti type structure with a space group of P 63/ mcm (No. 193) and lattice parameters of a = b = 8.9845 A and c = 5.8897 A. The structure contains face-sharing octahedral CrAs6 chains along the c -axis, which are arranged triangularly in the ab -plane and separated by a significantly large distance of 8.9845 A. The magnetic properties, resistivity and specific heat measurements were performed. La3CrAs5 exhibits a metallic state with Fermi liquid behavior at low temperatures and undergoes a ferromagnetic transition at Curie temperature T C ~50 K. First-principles theoretical studies were conducted to calculate its band structure and density of states (DOS), which indicated that the non-negligible contribution of La to the DOS near the Fermi level caused La3CrAs5 to be a three-dimensional (3D) metal. The crystal orbital Hamilton population (−COHP) was also calculated to explain the global stability and bonding characteristics in the structure of La3CrAs5.

Crystal Structure and Electronic Properties of New Compound Zr6.5Pt6Se19.

A new ternary nonstoichiometric Zr6.5Pt6Se19 has been discovered as a part of effort to dope Zr into the layered transitional metal chalcogenide PtSe2. With a new structure type (oC68), it is the first Pt-based ternary chalcogenide with group 4 elements (Ti, Zr, and Hf). The crystal structure adopts the orthorhombic space group Cmmm with lattice parameters of a = 15.637(6) Å, b = 26.541(10) Å, c = 3.6581(12) Å, and V = 1518.2(9) Å3. This unusual structure consists of several building units: chains of edge-sharing selenium trigonal prisms and octahedra centered by zirconium atoms, chains of corner-shared square pyramid, and square planar centered by Pt atoms. The condensation of these building blocks forms a unique structure with bilayered Zr5.54Pt6Se19 slabs stacking along the b direction and large channels parallel to the c direction within the bilayered slabs. Band structure calculations suggest that partial occupancy of Zr atoms creates a pseudo gap at the Fermi level and is likely the main cause for the stability of this new phase.