Search

Cs2Cu3(SeO3)4·2H2O is a ferrimagnet and exhibits a highly anisotropic 1/3-magnetization plateau. The necessary requirements for observing magnetic plateaus were explored by analyzing the topology of magnetic bonding.

We report on the magneto-structural properties of the rare copper aluminum hydroxo-arsenate mineral liroconite with chemical composition Cu2AlAs1−x P x O4(OH)4·4H2O (x ≈ 0.2). In order to characterize the natural mineral sample chemical analyses, X-ray single crystal and powder diffraction, heat capacity and crystal water desorption, anisotropic thermal expansion and Raman scattering and magnetic susceptibility investigations have been carried out. The magnetic properties are well described by two discrete oxygen bridged Cu2+ spin S = 1/2 dimers with antiferromagnetic spin exchange ranging between −320 K and −136 K, depending on to which group-15 five-valent cation, As5+ or P5+, the dimer bridging oxygen atoms coordinate to. Accordingly the temperature dependence of the magnetic susceptibilities can be well fitted to a sum of two Bleaney–Bowers type spin S = 1/2 dimer susceptibilities suggesting that the dimers show negligible mixed coordination to (AsO4)3−/(PO4)3− tetrahedra. DFT + U calculation confirm the ratio of the spin exchange parameters of the (AsO4)3− or (PO4)3− coordinated Cu2+ – Cu2+ dimers. Inter dimer spin exchange is about two orders of magnitude smaller than intra dimer exchange.

Sr2Be2B2O7 (SBBO) has long been considered as one of the most promising deep-ultraviolet nonlinear optical materials, but its crystal structure described by space group P6c2 in previous studies has remained questionable. On the basis of first-principles calculations coupled with the high-throughput crystal structure prediction method, we found three energetically favorable structures for SBBO with space groups Cm, Pm, and P6. These structures and a superstructure of space group Pm-S derived from the Cm structure were refined by the Rietveld method using the available powder X-ray diffraction data. These analyses show that the Pm-S structure is the best one, but its parent Cm structure is almost equally good and has the advantage of having higher symmetry. Via atom response theory analysis, we resolved the cause for the second-harmonic generation (SHG) responses of SBBO at the atomic and orbital level to elucidate the importance of local inversion symmetry in reducing the SHG response.

We prepared Cs

The magnetic structure of NaYMnWO6 was determined by neutron powder diffraction measurements. Below 9 K, the magnetic structure is a helix to wave vector k = (0, 0.447, 1/2), in contrast with NaYNiWO6, which shows a transverse spin density wave with k = (0.47, 0, 0.49). By analyzing the differences in the spin exchanges of NaYMnWO6 and NaYNiWO6, and in the magnetic anisotropies of the Mn2+ (d5, S = 5/2) and the Ni2+ (d2, S = 1) ions, we show what factors govern the propagation direction of a noncollinear magnetic structure and whether it becomes a helix or a cycloid.

ConspectusThermoelectric (TE) materials have received much attention because of their ability to convert heat energy to electrical energy. At a given temperature

AA′3B4O12 quadruple perovskites, with magnetic A′ and non-magnetic B cations, are characterized by a wide range of complex magnetic structures. These are due to a variety of competing spin-exchange interactions up to the fourth nearest neighbours. Here, we synthesize and characterize the magnetic behaviour of the CaCo3Ti4O12 quadruple perovskite. We find that in the absence of an external magnetic field, the system undergoes antiferromagnetic ordering at 9.3 K. This magnetic structure consists of three interpenetrating mutually orthogonal magnetic sublattices. Under an applied magnetic field, this antiferromagnetic structure evolves into a canted ferromagnetic structure. In explaining these magnetic structures, as well as the seemingly unrelated magnetic structures found in other quadruple perovskites, we suggest a crucial role played by the underlying kagome lattices in these systems. All observed magnetic structures of these materials represent indeed one of the three possible ways to reduce spin frustration in the A′ site kagome layers. More specifically, our survey of the magnetic structures observed for quadruple perovskites AA′3B4O12 reveals the following three ways to reduce spin frustration, namely to make each layer ferromagnetic, to adopt a compromise 120° spin arrangement in each layer, or to have a magnetic structure with a vanishing sum of all second nearest-neighbour spin exchanges.

The good thermal stability of a phosphor is crucial for its practical applications. Unfortunately, in the past decades, only the Gurney–Mott equation was available to describe the relation between the luminescence properties of a phosphor and temperature, which is, however, phenomenological and not precise. In this work, we introduced a hypothesis that the lowering of the luminescence efficiency of a phosphor is caused by the heat generated during the luminescence process and can be reduced if the luminescence site dissipates the heat away. We verified this hypothesis by evaluating the thermal conductivities κ of their luminescence sites, the Eu atoms, in the three phosphors, SrLiAl3N4:Eu2+, Sr2Si5N8:Eu2+ and SrSiN2:Eu2+, as well as those of the Sr atoms in their hosts SrLiAl3N4, Sr2Si5N8 and SrSiN2. It is suggested that our new approach can be employed as a practical criterion to search for phosphor materials with efficient luminescence properties.

Neutron diffraction studies on magnetic solids composed of axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedra show that the ordered magnetic moments of their high-spin Co2+ (d7, S = 3/2) ions are greater than 3 μB, i.e., the spin moment expected for S = 3/2 ions, and increase almost linearly from 3.22 to 4.45 μB as the bond-length ratio rCo-X/rCo-O increases from 1.347 to 1.659 where rCo-X and rCo-O are the Co-X and Co-O bond lengths, respectively. These observations imply that the orbital moments of the Co2+ ions increase linearly from 0.22 to 1.45 μB with increasing the rCo-X/rCo-O ratio from 1.347 to 1.659. We probed this implication by examining the condition for unquenched orbital moment and also by evaluating the magnetic moments of the Co2+ ions based on DFT+U+SOC calculations for those systems of the CoO4X2 octahedra. Our work shows that the orbital moments of the Co2+ ions are essentially quenched and, hence, that the observations of the neutron diffraction studies are not explained by the current theory of magnetic moments. This discrepancy between experiment and theory urges one to check the foundations of the current theory of magnetic moments as well as the current method of neutron diffraction refinements for ordered magnetic structures.

The incommensurate magnetic structure (0.47, 0, 0.49) of NaYNiWO6 exhibits unconventional spin-density waves (SDWs) along the [100] direction, in which up and down spins alternate in each half-wave. This is in contrast to conventional SDWs, in which only one type of spin is present in each half-wave. We probed the formation of these unconventional SDWs by evaluating the spin exchanges of NaYNiWO6 based on density functional theory calculations and analyzing the nature of the spin frustration in NaYNiWO6 and by noting that a SDW is a superposition of two cycloids of opposite chirality. The unconventional SDWs along the [100] direction originate from the spin-frustrated antiferromagnetic chains of Ni2+ ions along that direction, leading to conventional SDWs along the [101] direction and unconventional SDWs along the [001] direction.

The rate-determining step of the photoelectrochemical (PEC) water splitting is the water oxidation reaction at the photoanode, which is 4 orders of magnitude slower than the water reduction reactio...

In the presence of the roughly flat sequestering agent, [K(18-crown-6)]+, the reaction of Rh2(CO)4Cl2 with K5Bi4 in ethylenediamine (en) solution at room temperature yielded the heterometallic cluster anion [Rh@Bi10(RhCO)6]3- (1), in which two hitherto unknown Binm- building blocks (i.e., Bi6 crown and Bi4 pyramid) were stabilized by six +Rh-CO units. When the reaction was carried out at 60 °C using Rh(acac)(CO)2 (acac = acetylacetonate) as the source of +Rh-CO units, one obtained the anion [Rh@Bi9(RhCO)5]3- (2) in which two different Binn- units (n = 2, 3) and two weakly bonded Bi atoms were stabilized by five +Rh-CO units. The structures and bonding of the novel heterometallic cluster anions 1 and 2 were discussed.

Materials with two-dimensional, geometrically frustrated, spin-1/2 lattices provide a fertile playground for the study of intriguing magnetic phenomena such as quantum spin liquid (QSL) behavior, b...

The static and dynamic magnetic properties and the specific heat of K

Density functional theory calculations were carried out to probe the nature of the electronic structure change in TiPO

As early as 2001, the need for the ‘functional motif theory’ was pointed out, to assist the rational design of functional materials. The properties of materials are determined by their functional motifs and how they are arranged in the materials. Uncovering functional motifs and their arrangements is crucial in understanding the properties of materials and rationally designing new materials of desired properties. The functional motifs of materials are the critical microstructural units (e.g. constituent components and building blocks) that play a decisive role in generating certain material functions, and can not be replaced with other structural units without the loss, or significant suppression, of relevant functions. The role of functional motifs and their arrangement in materials, with representative examples, is presented. The microscopic structures of these examples can be classified into six types on a length scale smaller than ∼10 nm with maximum subatomic resolution, i.e. crystal, magnetic, aperiodic, defect, local and electronic structures. Functional motif analysis can be employed in the function-oriented design of materials, as elucidated by taking infrared non-linear optical materials as an example. Machine learning is more efficient in predicting material properties and screening materials with high efficiency than high-throughput experimentation and high-throughput calculations. In order to extract functional motifs and find their quantitative relationships, the development of sufficiently reliable databases for material structures and properties is imperative.

Two-dimensional (2D) transition metal oxide monolayers are currently attracting great interest in materials research due to their versatility and tunable electronic and magnetic properties. In this study, we report the prediction of magnetic phase changes in H x CrO2 (0 ⩽ x ⩽ 2) monolayer on the basis of first-principles calculations. As the H adsorption concentration x increases from 0 to 0.75, H x CrO2 monolayer transforms from a ferromagnetic (FM) half-metal to a small-gap FM insulator. When x = 1.00 and 1.25, it behaves as a bipolar antiferromagnetic (AFM) insulator, and eventually becomes an AFM insulator as x increases further up to 2.00. The results suggest that the magnetic properties of CrO2 monolayer can be effectively controlled by hydrogenation, and that H x CrO2 monolayers have the potential for realizing tunable 2D magnetic materials. Our results provide a comprehensive understanding of the hydrogenated 2D transition metal CrO2 and provide a research method that can be used as a reference for the hydrogenation of other similar 2D materials.

We examined what interactions control the sign and strength of the interlayer coupling in van der Waals ferromagnets such as Fe3-xGeTe2, Cr2Ge2Te6, CrI3 and VI3, to find that high-spin orbital interaction across the van der Waals gaps are a key to understanding their ferromagnetism. Interlayer ferromagnetic coupling in Fe3-xGeTe2 Cr2Ge2Te6, and CrI3 is governed by the high-spin two-orbital two-electron destabilization, but that in VI3 by the high-spin four-orbital two-electron stabilization. These interactions explain a number of seemingly puzzling observations in van der Waals fer-romagnets., Comment: 17 pages, 11 figures

Heat-induced blueshift (HIB) observed in many luminescent materials is a puzzling phenomenon that has remained unexplained for decades. By using the high-throughput first-principles calculations and energy-screening techniques, we generated a number of model structures for five phosphors, RbLi[Li

Sr

The second harmonic generation (SHG) responses of the paraelectric and ferroelectric phases of KH2PO4 (KDP) were calculated by first-principles density functional theory (DFT) calculations, and the individual atom contributions to the SHG responses were analyzed by the atom response theory (ART). We show that the occurrence of static polarization does not enhance the SHG responses of the ferroelectric KDP, and that the Kleinman symmetry is reasonably well obeyed for the paraelectric phase, but not for the ferroelectric phase despite that the latter has a larger bandgap. This is caused most likely by the fact that the ferroelectric phase has lower-symmetry local structures than does the paraelectric phase. The contribution to the SHG response of an individual K+ ion is comparable to that of an individual O2− ion. The contributions of the O2− and K+ ions arise overwhelmingly from the polarizable parts of the electronic structure, namely, from the valence bands of the O-2p nonbonding states and from the conduction bands of the K-3d states.

Magnetic topological insulators (TIs), including the quantum anomalous Hall effect and antiferromagnetic TIs, have attracted significant attention owing to the exotic properties they give rise to, however, ferromagnetic TIs with gapless surface/edge states and a nonzero topological invariant have not been reported so far. Here, we show that a ferromagnetic topological insulating phenomenon is possible in a single layer honeycomb lattice on the basis of perturbation theory and model Hamiltonian analyses. As a probable candidate for the experimental realization of this phenomenon, we propose a hypothetical single-layer Na2MnPb with supporting evidence based on first-principles calculations. The topological nature of the single-layer Na2MnPb is confirmed by calculating the Wannier charge center, the spin Chern number, and the gapless edge states.

In implementing the materials genome approach to search for new materials with interesting properties or functions, it is necessary to find the correct functional motif. To this end, it is common to partition an extended structure into various building units and then partition its properties to find the appropriate functional motif. We have developed the general principles for partitioning a structure and its properties in terms of a set of atoms and bonds by analyzing the differential cross-sections of neutron and X-ray scattering phenomena and proposed the procedures with which to partition an extended structure and its properties. We demonstrate how these procedures work by analyzing the nonlinear optical crystal KBe2BO3F2. Our partitioning analysis of KBe2BO3F2 leads to the conclusion that the second harmonic generation response of KBe2BO3F2 is dominated by the ionically bonded metal-centered groups.

We investigated the thermoelectric properties of the layered ternary selenides A2Sb4Se8 (A = K, Rb and Cs) and the lattice thermal conductivity of K2Sb4Se8 on the basis of DFT calculations, to find that these selenides are a high-performance n-type thermoelectric material. The Seebeck coefficients and power factors calculated for the electron carriers of A2Sb4Se8 (A = K, Rb and Cs) are greater than those of the well-known thermoelectric materials Bi2Te3 and PbTe. The lattice thermal conductivity κlatt of K2Sb4Se8 is comparable to that of PbTe, well-known for its low lattice thermal conductivity. In terms of both electronic and phonon structures, the structural parts of the A2Sb4Se8 (A = K, Rb and Cs) phases crucial for their thermoelectric properties are the conformationally-flexible Sb–Se–Se–Sb bridges that interlink between their structurally rigid units.

Two seemingly puzzling observations on two magnetic systems were analyzed. For the oxide-hydrides Sr2VO3H, Sr3V2O5H2, and SrVO2H, made up of VO4H2 octahedra, the spin orientations of the V3+ (d2, S = 1) ions were reported to be different, namely, perpendicular to the H-V-H bond in Sr2VO3H but parallel to the H-V-H bond in Sr3V2O5H2 and SrVO2H, despite that the d-state split patterns of the VO4H2 octahedra are similar in the three oxide-hydrides. Another puzzling observation is the contrasting magnetic structures of Sr2CoO2Cu2Te2 and Sr2MnO2Cu1.58Te2, consisting of the layers made up of corner-sharing MO4Te2 (M = Co, Mn) octahedra. The Co2+ spins in each CoO2Te2 layer are antiferromagnetically coupled with spins perpendicular to the Te–Co–Te bond, whereas the Mn3+/Mn2+ ions of each MnO2Te2 layer are ferromagnetically coupled with spins parallel to the Te-Mn-Te bonds. We investigated the cause for these observations by performing first-principles density functional theory (DFT) calculations for stoichiometr...

So far, most efforts in photocatalysis have been devoted to the separation of photogenerated electron-hole pairs, and possible use of excitons (i.e., electron-hole pairs) for photocatalytic processes has not received much attention. In this work, we studied the effect of metal dots on the excitonic behaviors of two bismuth-based MOFs, Bi-TATB and Bi-BTC (here the tridentate ligands TATB3− and BTC3− represent the carboxylates of 4,4′,4′'-s-triazine-2,4,6-triyl-tribenzoic and 1,3,5-benzenetricarboxylic acids, respectively). The organic ligands (TATB and BTC) display different emission properties from the corresponding Bi based MOFs. Specifically, TATB and BTC display strong fluorescence emission while Bi-TATB and Bi-BTC display strong phosphorescence emission, suggesting the higher efficiency of intersystem crossing for Bi-TATB and Bi-BTC. The reason is attributed to the coordination with Bi, which promotes the singlet→ triplet intersystem crossing of the organic ligand due to the heavy metal effect. The enhanced triplet excited emission of Bi-TATB and Bi-BTC was further confirmed by the detection of 1O2, as 1O2 is well known to be formed due to energy transfer from the triplet state of photosensitizers to the ground-state oxygen (3O2). With above understanding, Bi-TATB and Bi-BTC were finally used to high selective photooxidation of benzyl alcohol to benzaldehyde. This work presents new understanding of the photophysical properties of Bi based MOFs, which provides alternative ideas on designing materials for selective photo-oxidation.

UiO-67 is a Zr-based metal–organic framework (MOF) containing an organic linker namely, the dianion of biphenyl-4,4′-dicarboxylic acid (bpdc). Ce4+ metal ions (0.02 Ce to Zr atom ratio) were incorporated into UiO-67 via partially replacing bpdc with the dianion of 2,2′-bipyridine-5,5′-dicarboxylic acid (bpydc); thus, the latter forms a bpydc-Ce complex. The resulting product (i.e., UiO-67-Ce) demonstrated a photocatalytic hydrogen evolution rate that was over 10 times higher than that of UiO-67. Through this modification, a new energy transfer channel is opened up. The energy transfer between the bpdc and bpydc-Ce ligands (i.e., from excited bpdc to bpydc-Ce) weakened the recombination of the charge carriers, which was confirmed by photoluminescence, emission lifetime, and transient absorption measurements. This study presents a new way to construct highly efficient MOF photocatalysts.

Magnetic ions M in discrete molecules and extended solids form MLn complexes with their first-coordinate ligand atoms L. The spin moment of M in a complex MLn prefers a certain direction in coordin...

A simple and efficient light-assisted method is employed to prepare powder samples of all-inorganic mixed-perovskite CsPbBr3-xIx from CsPbBr3 by ion exchange in aqueous HBr/KI solution such that the concentration of I in a sample particle decreases on going from the surface to the interior. CsPbBr3-xIx/Pt, namely, CsPbBr3-xIx samples loaded with Pt nanoparticles, shows a high performance for the hydrogen evolution under visible-light irradiation in aqueous HBr solution saturated with CsPbBr3. The H2 evolution rate of the CsPbBr3-xIx/Pt powders (200 mg) is determined to be 224 μmol h−1, under 120 mW cm-2 visible-light (λ ≥ 420 nm) illumination. The CsPbBr3-xIx samples have a high stability, with no apparent decrease in the catalytic activity after 50 h of repeated H2 evolution experiments. The apparent quantum efficiency of CsPbBr3-xIx/Pt is determined to be 2.15% under the irradiation of 450 nm light.

The development in materials science and pharmaceutics shows that there exist some key materials genomes, i.e., certain groups of atoms with specific constituents and structures, which govern the property of a series of materials based on them. To pinpoint such materials, genomes are helpful to assemble functional units and synthesize new materials and, thus, have a profound meaning. In this work, we develop an innovative method based on the idea of projecting atomic orbitals’ wavefunction, which enables us to project every physical quantity into their orbital contribution and, thus, can be widely used to identify the materials genomes of various properties. Within this framework, we derive the expressions of the projected optical susceptibilities and exhibit a paradigm of studying the corresponding materials genomes of optical properties, especially the desired nonlinear optical materials.

Concerning the magnetic anisotropy and magnetic moments of the ${M}^{3+}$ $(M=\mathrm{V}, \mathrm{Cr})$ ions in ferromagnetic $(\mathrm{FM}){M\mathrm{I}}_{3}$ monolayers, which have a honeycomb pattern of edge-sharing ${M\mathrm{I}}_{6}$ octahedra, conflicting observations have been reported in experimental and theoretical studies. We resolve these conflicts by determining the magnetic anisotropy energies for the ${M}^{3+}$ ions of ${M\mathrm{I}}_{3}$ monolayers, by analyzing their preferred spin orientations in terms of the selection rules based on the highest occupied molecular orbital--lowest unoccupied molecular orbital interactions of the ${M\mathrm{I}}_{6}$ octahedra, and by discussing whether or not the ${M}^{3+}$ ions are uniaxial. Here we show that the FM monolayer ${\mathrm{VI}}_{3}$ is uniaxial, but that of ${\mathrm{CrI}}_{3}$ is not. The magnetic anisotropy energy for the ${\mathrm{V}}^{3+}({d}^{2},S=1)$ ion of ${\mathrm{VI}}_{3}$ is greater than that for the ${\mathrm{Cr}}^{3+}$ $({d}^{3},$ $S=3/2)$ ion of ${\mathrm{CrI}}_{3}$ by more than an order of magnitude (i.e., \ensuremath{\sim}8 vs \ensuremath{\sim}0.6 meV). The ${\mathrm{V}}^{3+}$ ion exhibits uniaxial magnetism because its orbital quantum number L is not zero $(L=\phantom{\rule{0.16em}{0ex}}1)$, in contrast to the ${\mathrm{Cr}}^{3+}$ ion $(L=0)$.

Neutron diffraction studies on magnetic solids composed of axially elongated CoO

The incommensurate magnetic structure (0.47, 0, 0.49) of NaYNiWO

In implementing the materials genome approach to search for new materials with interesting properties or functions, it is necessary to find the correct functional motif. To this end, it is common to partition an extended structure into various building units and then partition its properties to find the appropriate functional motif. We have developed the general principles for partitioning a structure and its properties in terms of a set of atoms and bonds by analyzing the differential cross-sections of neutron and X-ray scattering phenomena and proposed the procedures with which to partition an extended structure and its properties. We demonstrate how these procedures work by analyzing the nonlinear optical crystal KBe2BO3F2. Our partitioning analysis of KBe2BO3F2 leads to the conclusion that the second harmonic generation response of KBe2BO3F2 is dominated by the ionically bonded metal-centered groups.

In the presence of the roughly flat sequestering agent, [K(18-crown-6)]

To produce hydrogen economically by electrolysis of water, one needs to develop a non-precious-metal catalyst that is as efficient as platinum metal. Here, we prepare such a catalyst by growing a layer of Mo2N over a layer of CeO2 deposited on nickel foam (NF) [hereafter, Mo2N /CeO2@NF] and show that the activity of this self-supported catalyst for hydrogen evolution in 1.0 M KOH is more efficient than that of the Pt/C electrode, achieving a current density of 10 mA/cm2 at a fairly low overpotential of 26 mV. Furthermore, after a long-time electrochemical stability test for 24 h at a fixed current density, the overpotential needed to attain a current density of 10 mA/cm2 is increased only by 6 mV, implying the huge potential of this method to prepare a super HER activity electrode for water splitting.

We constructed a composite electrode by depositing a C/Ag mixture containing a tiny amount of 20 nm Ag NPs (∼0.5 wt%) on anodized Zn (AZ) metal. The AZ/C/Ag electrode exhibits greatly enhanced CO selectivity (∼86%) and activity (∼7.3 mA cm−2) on comparison with the GCE/C/Ag electrode (∼24% and ∼2.3 mA cm−2). The experimental results show that the enhanced CO2 reduction performance of the AZ/C/Ag electrode is attributed to the synergistic effect of AZ, C and Ag. Density functional theory calculations indicate that the enhanced CO selectivity may originate from the enhanced stabilization of CO2 and COOH* on the AZ/C/Ag electrode surface. This electrode also shows great mass activity and stability for CO2 reduction. Our work provides a new and simple way to fabricate efficient catalysts with high selectivity, activity and stability for electrocatalytic CO2 reduction.

Though titanium-based metal-organic frameworks (MOFs) are declared to be relatively water stable, their framework gradually collapses in water within days due to the attack of OH− to O Ti O bond. For practical applications of titanium-based MOFs, it is crucial to solve their instability problem in water. We searched for a simple and efficient method to enhance the stability of titanium-based MOFs in water by using Ti-ATA (ATA = 2-aminoterephthallate ion) as a representative titanium-based MOF. Here, we show that the stability of Ti-ATA in water is greatly improved nearly without affecting its porosity and photocatalytic activity by treating it with aqueous solutions containing metal ions of empty d orbitals (Y3+, La3+, Ce3+, Nd3+ and Tm3+) or partially-filled d orbitals (Cr3+).

The second harmonic generation (SHG) responses of the paraelectric and ferroelectric phases of KH

Materials with two-dimensional, geometrically frustrated, spin

An orthorhombic compound, $\mathrm{NaMnSb}{\mathrm{O}}_{4}$, represents a square net of magnetic $\mathrm{M}{\mathrm{n}}^{2+}$ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and density-functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with ${T}_{\mathrm{N}}\ensuremath{\sim}44\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is preceded by a short-range one at about 55 K. In addition, a nontrivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of two-dimensional square-lattice model with the main exchange parameter $J=\ensuremath{-}5.3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, which is in good agreement with density-functional analysis, NMR, and ESR data.

We investigated the thermoelectric properties of the layered ternary selenides A

We determined the spin exchanges between the Cu2+ ions in the kagome layers of volborthite, Cu3V2O7(OH)2x2H2O, by performing the energy-mapping analysis based on DFT+U calculations, to find that the kagom\'e layers of Cu2+ ions are hardly spin-frustrated, and the magnetic properties of volborthite below ~75 K should be described by very weakly interacting antiferromagnetic uniform chains made up of effective S=1/2 pseudospin units. This conclusion was verified by synthesizing single crystals of not only Cu3V2O7(OH)2x2H2O but also its deuterated analogue Cu3V2O7(OD)2x2D2O and then by investigating their magnetic susceptibilities and specific heats. Each kagome layer consists of intertwined two-leg spin ladders with rungs of linear spin trimers. With the latter acting as S=1/2 pseudospin units, each two-leg spin ladder behaves as a chain of S=1/2 pseudospins. Adjacent two-leg spin ladders in each kagome layer interact very weakly, so it is required that all nearest-neighbor spin exchange paths of every two-leg spin ladder remain antiferromagnetically coupled in all spin ladder arrangements of a kagome layer. This constraint imposes three sets of entropy spectra with which each kagome layer can exchange energy with the surrounding on lowering the temperature below ~1.5 K and on raising the external magnetic field B. We discovered that the specific heat anomalies of volborthite observed below ~1.5 K at B = 0 are suppressed by raising the magnetic field B to ~4.2 T, that a new specific heat anomaly occurs when B is increased above ~5.5 T, and that the imposed three sets of entropy spectra are responsible for the field-dependence of the specific heat anomalies., Comment: 36 pages incl. Supplementary Information

NiV-LDH as a novel electrode material has rarely been investigated in the energy storage field. Herein, novel ultrathin NiV-LDH was designed and synthesized, which displays high specific capacitance but poor stability. To further improve the stability, NiV-LDH was transformed to the sulfide named NiV-S through an ion exchange reaction (S2− replaces OH−). The obtained NiV-S maintains the ultrathin (5 nm in thickness) and porous structure, and displays higher specific capacitance (2270.4 F g−1 at 2 A g−1), compared to NiV-LDH (1502 F g−1 at 2 A g−1). What is more improtant is that the cycling stability of NiV-S is much higher than NiV-LDH, (91.9% retention after 10,000 cycles for NiV-S vs only 63% retention after 5000 cycles for NiV-LDH). The asymmetric supercapacitor assembled using ultrathin porous NiV-S as the positive electrode and activated carbon (AC) as the negative electrode was found to deliver a maximum energy density of 51 W h kg−1 at a power density of 1600 W kg−1 and 12 kW kg−1 at 23.7 W h kg−1. In addition, 98.5% of the initial capacitance retains after 10,000 continuous cycling.