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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.

Mixed-valent Ba2Mn2+Mn23+(SeO3)6 crystallizes in a monoclinic P21/c structure and has honeycomb layers of Mn3+ ions alternating with triangular layers of Mn2+ ions. We established the key parameters governing its magnetic structure by magnetization M and specific heat Cp measurements. The title compound exhibits a close succession of a short-range correlation order at Tcorr = 10.1 ± 0.1 K and a long-range Néel order at TN = 5.7 ± 0.1 K, and exhibits a metamagnetic phase transition at T < TN with hysteresis most pronounced at low temperatures. The causes for these observations were found using the spin exchange parameters evaluated by density functional theory calculations. The title compound represents a unique case in which uniform chains of integer spin Mn3+ (S = 2) ions interact with those of half-integer spin Mn2+ (S = 5/2) ions.

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.

International audience; Oxychalcogenides are promising candidates for the design of IR nonlinear optical materials. Here, we prepared the first oxysulfide in the polar Fresnoite mineral type, Ba2SnSSi2O7 , and show that it has rare tin square pyramids, SnO4S, with apical Sn-S bond. These units and the Si2O7 groups are corner-shared to form the SnSSi2O7 layer with their Sn-S and apical Si-O bonds pointed along the polar c axis. Second harmonic generation measurements reveal that Ba2SnSSi2O7 is an IR NLO compound. Formally, Ba2SnSSi2O7 results from the mineral Fresnoite, Ba2TiOSi2O7 , by replacing the TiO5 square pyramid with the SnO4S square pyramid. This substitution increases the apical/the equatorial bond ratio of the square pyramid, namely, Ti-Oap /Ti-Oeq = 1.66/2.00 = 0.83 in TiO5 , and Sn-S/Sn-O = 2.03/2.31 = 0.88 in SnO4S. This change has a major impact on the cleavage along the stacking polar c-axis and on the second harmonic generation response, which decreases from Ba2TiOSi2O7 to Ba2SnSSi2O7 by a factor greater than two. The atom response theory analyses based on the density functional theory calculations reveal a remarkable difference between Ba2TiOSi2O7 and Ba2SnSSi2O7 ; the second harmonic generation is positive for the Ti4+ ion of Ba2TiOSi2O7 , but negative for the Sn4+ ion of Ba2SnSSi2O7. A Tauc plot analysis for Ba2SnSSi2O7 assuming indirect and direct transitions led to the optical band gaps of 2.4 and 2.7 eV, respectively.

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

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.

The static and dynamic magnetic properties and the specific heat of K2Ni2TeO6 and Li2Ni2TeO6 were examined and it was found that they undergo a long-range ordering at TN = 22.8 and 24.4 K, respectively, but exhibit a strong short-range order. At high temperature, the magnetic susceptibilities of K2Ni2TeO6 and Li2Ni2TeO6 are described by a Curie–Weiss law, with Curie-Weiss temperatures Θ of approximately −13 and −20 K, respectively, leading to the effective magnetic moment of about 4.46 ± 0.01 µB per formula unit, as expected for Ni2+ (S = 1) ions. In the paramagnetic region, the ESR spectra of K2Ni2TeO6 and Li2Ni2TeO6 show a single Lorentzianshaped line characterized by the isotropic effective g-factor, g = 2.19 ± 0.01. The energy-mapping analysis shows that the honeycomb layers of A2Ni2TeO6 (A = K, Li) and Li3Ni2SbO6 adopt a zigzag order, in which zigzag ferromagnetic chains are antiferromagnetically coupled, because the third nearest-neighbor spin exchanges are strongly antiferromagnetic while the first nearest-neighbor spin exchanges are strongly ferromagnetic, and that adjacent zigzag-ordered honeycomb layers prefer to be ferromagnetically coupled. The short-range order of the zigzag-ordered honeycomb lattices of K2Ni2TeO6 and Li2Ni2TeO6 is equivalent to that of an antiferromagnetic uniform chain, and is related to the short-range order of the ferromagnetic chains along the direction perpendicular to the chains. © 2022 by the authors. Licensee MDPI, Basel, Switzerland. Russian Foundation for Basic Research, РФФИ; Ministry of Education, MOE: 2020R1A6A1A03048004; National Research Foundation of Korea, NRF; Russian Science Foundation, RSF: 22-42-08002; Government Council on Grants, Russian Federation: 075-15-2021-604 Funding: This work was supported by the grant 14-03-01122 from the Russian Foundation for Basic Research (VBN), by the Russian Scientific Foundation through Grant No. 22-42-08002, and by the Mega-grant program of the Government of Russian Federation through the project 075-15-2021-604. The work at KHU was financially supported by the Basic Science Research Program through the National Research Foundation (NRF) of Korea, which was funded by the Ministry of Education (2020R1A6A1A03048004).

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

International audience; John B. Goodenough won the Nobel Prize in Chemistry in 2019 with Stanley Wittingham and Akira Yoshino for their fundamental contributions to the development of lithium-ion batteries. Calls for recognition for John’s pioneering work on lithium-ion batteries had been launched at the Nobel Committee for many years and finally the calls were answered! This was wonderful, though long overdue, news for the communities of solid-state chemistry and materials sciences. John impacted these areas of research greatly via his constant desire to account for the physical properties of solids through the discussion of their local crystal structures and their chemical bonding. Let us notice that, on this special occasion, John also set the record for being the oldest person, at 97, to receive this prestigious honor!

Thin films of Ca-doped double perovskite, PrBa0.7Ca0.3Co2O5+δ (PBCC), were epitaxially grown on (001) SrTiO3, and their redox reactions under a switching flow of H2 and O2 gases were examined at various temperatures by measuring the resistance R(t) of the films as a function of the gas flow time t. In the temperature range between 350 and 725 °C, these thin films are reduced and oxidized in an ultrafast manner under the flow of H2 and O2 gases, respectively, suggesting that PBCC thin films are promising candidates for developing ultra-sensitive oxygen sensors or SOFC cathodes at intermediate or high temperatures. When the gas flow is switched to O2, the reduced PBCC thin films exhibit a negative resistance at temperatures above 600 °C but a positive resistance at temperatures below 600 °C. The probable cause for these anomalous transport properties is the diffusion of the H atoms from the cathode to the anode in the PBCC film, which provides a current opposite to that resulting from the external voltage.

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.