Mechanical forces exerted on floral primordia with a novel experimental system modify floral development in Arabidopsis thaliana.

Mechanical forces play a crucial role in plant development, including floral development. We previously reported that the phyllotactic variation in the staminate flowers of Ceratophyllum demersum may be caused by mechanical forces on the adaxial side of floral primordia, which may be a common mechanism in angiosperms. On the basis of this result, we developed a novel experimental system for analysis of the effects of mechanical forces on the floral meristem of Arabidopsis thaliana, aiming to induce morphological changes in flowers. In this experimental system, a micromanipulator equipped with a micro device, which is shaped to conform with the contour of the abaxial side of the young floral primordium, is used to exert contact pressure on a floral primordium. In the present study, we conducted contact experiments using this system and successfully induced diverse morphological changes during floral primordial development. In several primordia, the tip of the abaxial sepal primordium was incised with two or three lobes. A different floral primordium developed an additional sepal on the abaxial side (i.e., two abaxial sepals). Additionally, we observed the fusion of sepals in some floral primordia. These results suggest that mechanical forces have multiple effects on floral development, and changes in the tensile stress pattern in the cells of floral primordia are induced by the mechanical forces exerted with the micro device. These effects, in turn, lead to morphological changes in the floral primordia.

Origin of O2 Generation in Sulfide-Based All-Solid-State Batteries and its Impact on High Energy Density.

The cathode surface of sulfide-based all-solid-state batteries (SBs) is commonly coated with amorphous-LiNbO3 in order to stabilize charge-discharge reactions. However, high-voltage charging diminishes the advantages, which is caused by problems with the amorphous-LiNbO3 coating layer. This study has investigated the degradation of amorphous-LiNbO3 coating layer directly during the high-voltage charging of SBs. O2 generation via Li extraction from the amorphous-LiNbO3 coating layer is observed using electrochemical gas analysis and electrochemical X-ray photoelectron spectroscopy. This O2 leads to the formation of an oxidative solid electrolyte (SE) around the coating layer and degrades the battery performance. On the other hand, elemental substitution (i.e., amorphous-LiNbxP1- xO3) reduces O2 release, leading to stable high-voltage charge-discharge reactions of SBs. The results have emphasized that the suppression of O2 generation is a key factor in improving the energy density of SBs.

Signatures of a magnetic superstructure phase induced by ultrahigh magnetic fields in a breathing pyrochlore antiferromagnet.

The mutual coupling of spin and lattice degrees of freedom is ubiquitous in magnetic materials and potentially creates exotic magnetic states in response to the external magnetic field. Particularly, geometrically frustrated magnets serve as a fertile playground for realizing magnetic superstructure phases. Here, we observe an unconventional two-step magnetostructural transition prior to a half-magnetization plateau in a breathing pyrochlore chromium spinel by means of state-of-the-art magnetization and magnetostriction measurements in ultrahigh magnetic fields available up to 600 T. Considering a microscopic magnetoelastic theory, the intermediate-field phase can be assigned to a magnetic superstructure with a three-dimensional periodic array of 3-up-1-down and canted 2-up-2-down spin molecules. We attribute the emergence of the magnetic superstructure to a unique combination of the strong spin-lattice coupling and large breathing anisotropy.

High-Pressure Synthesis of Transition-Metal Oxyhydrides with Double-Perovskite Structures.

We report on the high-pressure synthesis, crystal structure, and magnetic properties of four novel transition-metal oxyhydrides─Ba2NaVO3H3, Ba2NaVO2.4H3.6, Ba2NaCrO2.2H3.8, and Ba2NaTiO3H3─crystallizing in the double-perovskite structure. Notably, they have a higher hydride content in their anion sites (50%-63%) than known oxyhydrides with perovskite structures do (≤33%). Vanadium and chromium oxyhydrides exhibited Curie-Weiss magnetic susceptibilities with no magnetic ordering down to 2 K, which may be due to geometrical frustration in their face-centered lattices and weak magnetic interactions. Density functional theory calculations revealed that the transition metal-hydride bonding nature of the prepared oxyhydrides is more covalent than that observed for known perovskite oxyhydrides, as evidenced by the shorter bond lengths of the former. Remarkably, our double-perovskite oxyhydrides with a high hydride content may possess a bonding character intermediate between those of known oxyhydrides and hydrides.

Ligand dependent magnetism of theJeff= 3/2 Mott insulator Cs2MX6(M= Ta, Nb,X= Br, Cl).

Magnetic and structural properties of double perovskite type bromides Cs2MBr6(M= Ta, Nb), where Ta4+(5d1) and Nb4+(4d1) ions form the face centered cubic lattice, are investigated and compared with chlorides Cs2MCl6. Cs2TaBr6exhibits the effective magnetic moment of 0.24µB, which is much smaller than the spin only value of ad1ion, 1.73µB, and comparable to 0.25µBin Cs2TaCl6. On the other hand, the effective magnetic moment of Cs2NbBr6is 0.7µBand is substantially smaller than 1.0µBin Cs2NbCl6. On cooling, successive structural and magnetic phase transitions accompanying the release of electronic entropy approximatelyRln 4 in total as expected for theJeff= 3/2 state are observed. The type of the ligand changes the temperature dependence of magnetic susceptibility at low temperature as well as its magnitude. The role of the ligands on the magnetism ofJeff= 3/2 Mott insulators are discussed in the light of metal-ligand hybridization and the electron-lattice coupling.

Pressure-Induced Collapse Transition in BaTi2Pn2O (Pn = As, Sb) with an Unusual Pn-Pn Bond Elongation.

Making and breaking bonds in a solid-state compound greatly influences physical properties. A well-known playground for such bonding manipulation is the ThCr2Si2-type structure AT2X2, allowing a collapse transition where a X-X dimer forms by a chemical substitution or external stimuli. Here, we report a pressure-induced collapse transition in the structurally related BaTi2Pn2O (Pn = As, Sb) at a transition pressure Pc of ∼15 GPa. The Pn-Pn bond formation is related with Pn-p band filling, which is controlled by charge transfer from the Ti-3d band. At Pc, the Sb-Sb distance in BaTi2Sb2O shrinks due to bond formation, but interestingly, the Sb-Sb expands with increasing pressure above Pc. This expansion, which was not reported in ThCr2Si2-type compounds, may arise from heteroleptic coordination geometry around titanium, where a compression of the Ti-O bond plays a role. Electrical resistivity measurements of BaTi2Sb2O up to 55 GPa revealed an increasing trend of the superconducting transition temperature with pressure. This study presents structure motifs that allow flexible bonding manipulation and property control with heteroleptic coordination geometry.

Nonmagnetic Ground States and a Possible Quadrupolar Phase in 4d and 5d Lacunar Spinel Selenides GaM_{4}Se_{8} (M=Nb, Ta).

Structural and magnetic properties of cubic spinel selenides GaM_{4}Se_{8} (M=Nb, Ta), which are candidates for the molecular J_{eff}=3/2 Mott insulators, are investigated. The effective magnetic moments are reduced compared to the spin only value, indicating the presence of sizable spin-orbit coupling. GaNb_{4}Se_{8} and GaTa_{4}Se_{8} exhibit phase transitions into the nonmagnetic ground states with orthorhombic and tetragonal structures, respectively, which are robust against magnetic field up to at least 60 T. A cubic-cubic phase transition is observed in GaNb_{4}Se_{8} preceding the magnetic transition, suggesting the existence of a quadrupolar-ordered phase theoretically predicted in the J_{eff}=3/2 Mott insulator.

Anisotropic Triangular Lattice Realized in Rhenium Oxychlorides A3ReO5Cl2 (A = Ba, Sr).

We report the synthesis, crystal structure, and magnetic properties of the two new quantum antiferromagnets A3ReO5Cl2 (A = Sr, Ba). The crystal structure is isostructural with the mineral pinalite Pb3WO5Cl2, in which the Re6+ ion is square pyramidally coordinated by five oxide atoms and forms an anisotropic triangular lattice (ATL) made of S = 1/2 spins. The magnetic interactions J and J' in the ATL are estimated from magnetic susceptibilities to be 19.5 (44.9) and 9.2 (19.3) K, respectively, with J'/J = 0.47 (0.43) for A = Ba (Sr). For each compound, the heat capacity at low temperatures shows a large T-linear component with no signature of long-range magnetic order above 2 K, which suggests a gapless spin liquid state of one-dimensional character of the J chains in spite of the significantly large J' couplings. This is a consequence of one-dimensionalization by geometrical frustration in the ATL magnet; a similar phenomenon has been observed in two compounds with slightly smaller J'/J values: Cs2CuCl4 (J'/J = 0.3) and the related compound Ca3ReO5Cl2 (0.32). Our findings demonstrate that 5d mixed-anion compounds provide a unique opportunity to explore novel quantum magnetism.

Titanium Hydride Complex BaCa2Ti2H14 with 9-Fold Coordination.

We present the high-pressure synthesis and crystal structure of a novel titanium hydride complex, BaCa2Ti2H14, with 9-fold coordination. It comprises a unique dinuclear [Ti2H14]6- complex that consists of a pair of Ti4+ ions each coordinated by nine hydrides in the monocapped square antiprism, distinguished from the known 9-fold coordination in the mononuclear tricapped trigonal prism of [MH9]x-. The dinuclear hydride complex is stabilized by three-center two-electron bonding at the four bridging Ti-H-Ti bonds to compensate for the lack of valence electrons in the Ti4+ ions. Optical measurements show that BaCa2Ti2H14 is a band insulator with a wide band gap of 2.25 eV. Density functional theory calculations reveal that the top of the valence band is dominated by H-1s-derived states, as expected from the 9-fold coordination, which would present a playground for electronic properties such as high-Tc superconductivity when doped with hole carriers or under high pressure.

Thermal-transport studies of kagomé antiferromagnets.

Searching for the ground state of a kagomé Heisenberg antiferromagnet (KHA) has been one of the central issues of condensed-matter physics, because the KHA is expected to host spin-liquid phases with exotic elementary excitations. Here, we show our longitudinal ([Formula: see text]) and transverse ([Formula: see text]) thermal conductivities measurements of the two kagomé materials, volborthite and Ca kapellasite. Although magnetic orders appear at temperatures much lower than the antiferromagnetic energy scale in both materials, the nature of spin liquids can be captured above the transition temperatures. The temperature and field dependence of [Formula: see text] is analyzed by spin and phonon contributions, and large sample variations of the spin contribution are found in volborthite. Clear changes in [Formula: see text] are observed at the multiple magnetic transitions in volborthite, showing different magnetic thermal conduction in different magnetic structures. These magnetic contributions are not clearly observed in low-[Formula: see text] crystals of volborthite, and are almost absent in Ca kapellasite, showing the high sensitivity of the magnetic excitation in [Formula: see text] to the defects in crystals. On the other hand, a clear thermal Hall signal has been observed in the lowest-[Formula: see text] crystal of volborthite and in Ca kapellasite. Remarkably, both the temperature dependence and the magnitude of [Formula: see text] of volborthite are found to be very similar to those of Ca kapellasite, despite of about an order of magnitude difference in [Formula: see text] We find that [Formula: see text] of both compounds is well reproduced, both qualitatively and quantitatively, by spin excitations described by the Schwinger-boson mean-field theory applied to KHA with the Dzyaloshinskii-Moriya interaction. This excellent agreement demonstrates not only that the thermal Hall effect in these kagomé antiferromagnets is caused by spins in the spin liquid phase, but also that the elementary excitations of this spin liquid phase are well described by the bosonic spin excitations.

Site Selectivity of Hydride in Early-Transition-Metal Ruddlesden-Popper Oxyhydrides.

Layered perovskite titanium oxyhydrides have been prepared by low-temperature topochemical CaH2 reduction from Ruddlesden-Popper Sr n+1Ti nO3 n+1 phases ( n = 1, 2) and structurally characterized by combined synchrotron X-ray and neutron diffraction data refinements. In the single-layered Sr2TiO3.91(2)D0.14(1) material, hydride anions are statistically disordered with oxides on the apical site only, as opposed to known transition-metal oxyhydrides exhibiting a preferred occupation of the equatorial site. This unprecedented site selectivity of H- has been reproduced by periodic DFT+ U calculations, emphasizing for the hydride defect a difference in formation energy of 0.24 eV between equatorial and apical sites. In terms of electronic structure, the model system Sr2TiO3.875H0.125 is found to be slightly metallic and the released electron remains mostly delocalized over several Ti atoms. On the other hand, hydride anions in the double-layered Sr3Ti2O6.20H0.12 material show a clear preference for the bridging apical site within the perovskite slabs, as confirmed by DFT calculations on the Sr3Ti2O6.875H0.125 model system. Finally, the influence of the B-site chemical nature on the hydride site selectivity for early 3d transition metals is theoretically explored in the single-layered system by substituting vanadium for titanium. The V3+ electronic polaron is suggested to play a role in stabilizing H- on the equatorial site in Sr2VO4- xH x for x = 0.125.

Promoted Hydride/Oxide Exchange in SrTiO3 by Introduction of Anion Vacancy via Aliovalent Cation Substitution.

We investigated topochemical anion exchange reactions for a ScIII-substituted SrTiIVO3 perovskite, Sr(Ti1-yScy)O3-y/2□y/2 (y ≤ 0.1), using CaH2. It was found that the initial introduction of a small amount of anion vacancies (y/2) is crucial to enhance the anion (H-/O2-) exchangeability. For example, hydride reduction of Sr(Ti0.95Sc0.05)O2.975 yielded the oxyhydride SrTi0.95Sc0.05O2.56H0.41 in which the hydride concentration is increased by 33% with respect to pristine SrTiO3 (leading to SrTiO2.76H0.24). This observation highlights the importance of anion vacancies to improve anion (H-/O2-) diffusion, which is a well-known strategy for improving oxide anion conductivity, and suggests that such a vacancy-assisted reaction could be applied to other anion exchange reactions (e.g., F-/O2- and N3-/O2-) to extend the solubility range.

"Visible" 5d Orbital States in a Pleochroic Oxychloride.

Transition metal compounds sometimes exhibit attractive colors. Here, we report a new oxychloride, Ca3ReO5Cl2, that shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. This pleochroism is a consequence of the coincidental complex crystal field splitting of the 5d orbitals of the Re6+ ion in a square-pyramidal coordination of low symmetry in the energy range of the visible spectrum. Since the relevant d-d transitions show characteristic polarization dependence according to the optical selection rule, the orbital states are "visible" in Ca3ReO5Cl2.

Selective and low temperature transition metal intercalation in layered tellurides.

Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid.

Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.

When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons.

A labile hydride strategy for the synthesis of heavily nitridized BaTiO3.

Oxynitrides have been explored extensively in the past decade because of their interesting properties, such as visible-light absorption, photocatalytic activity and high dielectric permittivity. Their synthesis typically requires high-temperature NH3 treatment (800-1,300 °C) of precursors, such as oxides, but the highly reducing conditions and the low mobility of N(3-) species in the lattice place significant constraints on the composition and structure-and hence the properties-of the resulting oxynitrides. Here we show a topochemical route that enables the preparation of an oxynitride at low temperatures (<500 °C), using a perovskite oxyhydride as a host. The lability of H(-) in BaTiO3-xHx (x ≤ 0.6) allows H(-)/N(3-) exchange to occur, and yields a room-temperature ferroelectric BaTiO3-xN2x/3. This anion exchange is accompanied by a metal-to-insulator crossover via mixed O-H-N intermediates. These findings suggest that this 'labile hydride' strategy can be used to explore various oxynitrides, and perhaps other mixed anionic compounds.

Orbital Arrangements and Magnetic Interactions in the Quasi-One-Dimensional Cuprates ACuMoO4(OH) (A = Na, K).

A new spin-1/2 quasi-one-dimensional antiferromagnet KCuMoO4(OH) is prepared by the hydrothermal method. The crystal structures of KCuMoO4(OH) and the already-known Na-analogue NaCuMoO4(OH) are isotypic, comprising chains of Cu(2+) ions in edge-sharing CuO4(OH)2 octahedra. Despite the structural similarity, their magnetic properties are quite different because of the different arrangements of dx(2)-y(2) orbitals carrying spins. For NaCuMoO4(OH), dx(2)-y(2) orbitals are linked by superexchange couplings via two bridging oxide ions, which gives a ferromagnetic nearest-neighbor interaction J1 of -51 K and an antiferromagnetic next-nearest-neighbor interaction J2 of 36 K in the chain. In contrast, a staggered dx(2)-y(2) orbital arrangement in KCuMoO4(OH) results in superexchange couplings via only one bridging oxide ion, which makes J1 antiferromagnetic as large as 238 K and J2 negligible. This comparison between the two isotypic compounds demonstrates an important role of orbital arrangements in determining the magnetic properties of cuprates.

A-site-ordered perovskite MnCu3V4O12 with a 12-coordinated manganese(II).

A novel cubic perovskite MnCu3V4O12 has been synthesized at a high pressure and high temperature of 12 GPa and 1373 K. This compound crystallizes in the A-site-ordered perovskite structure (space group Im3) with lattice constant a = 7.26684(10) Å at room temperature. The most notable feature of this compound lies in the fact that the Mn(2+) ion is surrounded by 12 equidistant oxide ions to form a regular icosahedron; the situation of Mn(2+) is unprecedented for the crystal chemistry of an oxide. An anomalously large atomic displacement parameter U(iso)= 0.0222(8) Å(2) is found for Mn(2+) at room temperature, indicating that the thermal oscillation of the small Mn(2+) ion in a large icosahedron is fairly active. Magnetic susceptibility and electric resistivity measurements reveal that 3d electrons of Mn(2+) ions are mainly localized, while 3d electrons in Cu(2+) and V(4+) ions are delocalized and contribute to the metallic conduction.

Molecular rotors of coronene in charge-transfer solids.

Ten types of neutral charge transfer (CT) complexes of coronene (electron donor; D) were obtained with various electron acceptors (A). In addition to the reported 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex of 1:1 stoichiometry with a DA-type alternating π column, TCNQ also afforded a 3:1 complex, in which a face-to-face dimer of parallel coronenes (Cor-As) is sandwiched between TCNQs to construct a DDA-type alternating π column flanked by another coronene (Cor-B). Whereas solid-state (2)H NMR spectra of the 1:1 TCNQ complex formed with deuterated coronene confirmed the single in-plane 6-fold flipping motion of the coronenes, two unsynchronized motions were confirmed for the 3:1 TCNQ complex, which is consistent with a crystallographic study. Neutral [Ni(mnt)2] (mnt: maleonitriledithiolate) as an electron acceptor afforded a 5:2 complex with a DDA-type alternating π column flanked by another coronene, similar to the 3:1 TCNQ complex. The fact that the Cor-As in the [Ni(mnt)2] complex arrange in a non-parallel fashion must cause the fast in-plane rotation of Cor-A relative to that of Cor-B. This is in sharp contrast to the 3:1 TCNQ complex, in which the dimer of parallel Cor-As shows inter-column interactions with neighboring Cor-As. The solid-state (1)H NMR signal of the [Ni(mnt)2] complex suddenly broadens at temperatures below approximately 60 K, indicating that the in-plane rotation of the coronenes undergoes down to approximately 60 K; the rotational rate reaches the gigahertz regime at room temperature. Rotational barriers of these CT complexes, as estimated from variable-temperature spin-lattice relaxation time (T1) experiments, are significantly lower than that of pristine coronene. The investigated structure-property relationships indicate that the complexation not only facilitates the molecular rotation of coronenes but also provides a new solid-state rotor system that involves unsynchronized plural rotators.

Oxyhydrides of (Ca,Sr,Ba)TiO3 perovskite solid solutions.

The oxyhydride solid solutions (Ca,Sr)TiO(3-x)H(x) and (Sr,Ba)TiO(3-x)H(x) have been prepared by reducing the corresponding ATiO(3) oxides with calcium hydride. Under the reaction conditions examined, a hydride content of x = 0.1-0.3 was obtained for all compositions. Compared to our previous result with BaTiO(3-x)H(x), the larger particle size in this study (20-30 µm vs 170 nm) resulted in a somewhat lower hydride amount despite prolonged reaction times. We examined changes in cell volume, octahedral tilt angle, and site occupancy of different anion sites after conversion to oxyhydrides; it appears that these oxyhydrides fit the geometrical descriptions typical for regular ABO(3) perovskites quite well. The hydrogen release temperature, previously shown to be indicative of the hydride exchange temperature, however, does not scale linearly with the A-site composition, indicating a potential effect of chemical randomness.