Unique Conduction Band Minimum of Semiconductors Possessing a Zincblende-Type Framework.

Tetrahedral semiconductors such as Si adopt a diamond-type crystal structure with low packing density arising from open cavities in the crystallographic space. By taking LiAlGe as an example, we propose a zincblende-type framework as a platform for semiconductors possessing electroactive cavities. LiAlGe adopts a half-Heusler-type crystal structure including an ordered diamond-type sublattice (zincblende-type) (AlGe) and is an indirect semiconductor with a band gap of ∼0.1 eV. The conduction band minimum (CBM) is uniquely located at the cavity space surrounded by four cations (Al4) in real space. The bond ionicity and cation (Al) p orbitals located around the Fermi energy are requisite for the CBM to float in the cavity space. DFT calculations indicate the conversion of the semiconductor to a semimetallic electride under a pressure of ∼8 GPa, which is accompanied by band gap collapse due to electron transfer from valence band maximum to the cavity space. The high-pressure electride of LiAlGe formed under a very small critical pressure is derived from the presence of inherent crystallographic cavities having deep orbital levels energetically. This finding suggests the possible utilization of electroactive cavity spaces in tetrahedral semiconductors, which are widely used in modern electronic devices.

A View on Formation Gap in Transition Metal Hydrides and Its Collapse.

Late transition metals (LTMs) do not form hydrides under conventional experimental conditions except for palladium (Pd). The incorporation of a small amount of metal with low electronegativity converts LTMs into hydrogen (H) storage intermetallics (IMs) such as LaNi5. We examined the critical property of the H absorbing ability of LTMs and found that the lattice softness of Pd is a unique parameter for H insertion. This idea is applicable to H storage IMs. Indeed, negatively charged LTM ions, such as Niδ- in LaNi5, play a crucial role in hydrogenation. These ions cause lattice softening, which renders H solution possible. As a result, we propose that lattice softness can be an effective criterion for the development of new H storage IMs.

Origin of Metallic Nature of Na3N.

Among inorganic clathrates, the inner cavity space rarely affects the electronic structure of the framework. We report that the anti-ReO3-type compound Na3N has a metallic nature irrespective of the stoichiometric chemical composition of simple representative elements and that this unusual nature originates from the collapse of the bandgap owing to the presence of a crystallographic cavity. We synthesized Na3N by the plasma-assisted nitridation of alkali metals, and diffuse reflectance measurements indicated a metallic nature. The introduction of nitrogen into the Na metal induced the formation of both the Na+ ion and the crystallographic cavity. The former increased the density of the lattice of Na+ ions to form a wide Na 3s conduction band. The latter interacted with the Na 3s band to enhance the bandwidth, resulting in the collapse of the bandgap. Na3N is a unique nitride, which possesses an electronically active cavity space.

Twinning by Merohedry and Thermal Expansion of Zeolitic Clathrasil Deca-dodecasil 3R.

Rhombohedral crystal particles of zeolitic clathrasil deca-dodecasil 3R (DDR), hydrothermally synthesized from a mixture consisting of fumed silica, water, and 1-adamantanamine, were characterized by single-crystal and powder X-ray diffractometry as a function of temperature and pole figure analysis. The crystallite was bounded by six equivalent {101̅1} faces and exhibited twin-free appearance, whereas the structure was resolved with the binary twin by merohedry, defined by the twin point group 3̅2'/m'1, consisting of two twin domains with nearly equal volume fractions. This twinning modifies the positions of O atoms in the Si-O-Si framework while preserving the positions of Si atoms that define the topology of polyhedral cages. This type of twinning therefore does not disrupt the microporous channels via the 8-membered rings of the 19-hedral cages and little disturbs the adsorption and permeation of gas molecules in DDR. The cell volume of DDR increased monotonically with an increase in temperature up to ∼673 K accompanied by an elongation perpendicular to the [0001] axis and a shrinkage along the [0001] axis. Above ∼673 K, the cell volume decreased with temperature. These positive and negative volume expansion coefficients observed in this study were roughly one-half and one-third of the values currently available.

Zeolitic Intermetallics: LnNiSi (Ln = La-Nd).

LnNiSi (Ln = La-Nd) comprising a three-dimensional NiSi framework has electrons in the crystallographic cavity space. In the temperature region 473-773 K, it accepts the insertion/de-insertion of hydrogen topotactically without a change in unitcell volume. The insertion of hydrogens into the cavity space is accompanied by a redox reaction with the orbitals of atoms constituting the cavity wall. Having small work functions, such intermetallic electrides exhibit metallic electrical and magnetic properties. Owing to a high electron-donating power and reversible exchange between hydrogen and the electrons, Ru5wt%-loaded LaNiSi powder worked as an efficient catalyst for ammonia synthesis under ambient pressure.

On the Origin of the Negative Thermal Expansion Behavior of YCu.

Among the intermetallics and alloys, YCu is an unusual material because it displays negative thermal expansion without spin ordering. The mechanism behind this behavior that is caused by the structural phase transition of YCu has yet to be fully understood. To gain insight into this mechanism, we experimentally examined the crystal structure of the low-temperature phase of YCu and discuss the origin of the phase transition with the aid of thermodynamics calculations. The result shows that the high-temperature (cubic CsCl-type) to low-temperature (orthorhombic FeB-type) structural phase transition is driven by the rearrangement of three covalent bonds, namely, Y-Cu, Y-Y, and Cu-Cu, which compete for the bonding energy and phonon entropy. At low temperatures, the mixing of Y and Cu does not take place easily because of the weak attractive force between these atoms expected from the small negative mixing enthalpy. This causes all three interactions to take part in the bonding, and Y and Cu are segregated to form an FeB-type structure, which is stabilized by internal energy. At higher temperatures, Cu ions are bound loosely with Y ions due to the large Y-Cu distance (3.01 Å), which results in large vibration entropy and stabilizes a CsCl-type crystal structure. In addition, the CsCl-type structure is reinforced by the Y-Y interaction between next-nearest neighbors, resulting in a smaller unit cell volume. The crystal structure has the simple cubic framework of Y containing Cu ions bound loosely at the cavity sites. The calculated frequency of the Y-like phonon modes is much higher than that of the Cu-like modes, indicating the presence of Y-Y covalent interactions in the CsCl-type phase.

Implementation and Evaluation of a Wide-Range Human-Sensing System Based on Cooperating Multiple Range Image Sensors.

A museum is an important place for science education for children. The learning method in the museum is reading exhibits and explanations. Museums are investing efforts to quantify interests using questionnaires and sensors to improve their exhibitions and explanations. Therefore, even in places where many people gather, such as in museums, it is necessary to quantify people's interest by sensing behavior of multiple people. However, this has not yet been realized. We aim to quantify the interest by sensing a wide range of human behavior for multiple people by coordinating multiple noncontact sensors. When coordinating multiple sensors, the coordinates and the time of each sensor differ. To solve these problems, coordinates were transformed using a simultaneous transformation matrix and time synchronization was performed using unified time. The effectiveness of this proposal was verified through experimental evaluation. Furthermore, we evaluated the actual museum content. In this paper, we describe the proposed method and the results of the evaluation experiment.

Cubic Fluorite-Type CaH2 with a Small Bandgap.

A cubic variant of CaH2 adopting a fluorite-type crystal structure was synthesized by cationic substitution with La or Y, yielding the first alkaline earth hydride-based with fluorite-type framework. The material has a bandgap of ∼2.5 eV (greenish yellow in color), which is much smaller than that of orthorhombic PbCl2-type CaH2 (4.4 eV) and is, in fact, the smallest among alkaline or alkaline earth metal hydrides reported to date. Analysis of the density functional theory band structure of cubic-CaH2 indicates that its conduction band minimum is formed mainly by the interaction between the Ca 3d eg orbitals around the crystallographic cavity defined by cubes of H- ions. The use of such cavities in the creation of low-lying conduction band minima by semiconductors is extremely rare, and has similarities to inorganic electrides.

Transformation of the Chromium Coordination Environment in LaCrAsO Induced by Hydride Doping: Formation of La2Cr2As2OyHx.

We report the synthesis of La2Cr2As2OyHx (0.1 < y < 1.6) oxyhydride solid solutions using a solid-state reaction under high pressure with a solid-state hydrogen source and exhibit an example of how H- doping can also promote structural changes: H- doping in LaCrAsO results in the formation of La2Cr2As2OyHx with the La2Fe2Se2O3-type layered structure. Remarkably, this transformation includes a change of the coordination number of Cr from 4 to 6, with the some of the H- being accommodated in new sites within the CrAs layers. In this way, H- not only serves as a conventional electron dopant by the substitution of O2- but also makes new bonds to the transition metals.

The Unique Electronic Structure of Mg2 Si: Shaping the Conduction Bands of Semiconductors with Multicenter Bonding.

The electronic structures of the antifluorite-type compound Mg2 Si is described in which a sublattice of short cation-cation contacts creates a very low conduction band minimum. Since Mg2 Si shows n-type conductivity without intentional carrier doping, the present result indicates that the cage defined by the cations plays critical roles in carrier transport similar to those of inorganic electrides, such as 12 CaO⋅7 Al2 O3 :e- and Ca2 N. A distinct difference in the location of conduction band minimum between Mg2 Si and the isostructural phase Na2 S is explained in terms of factors such as the differing interaction strengths of the Si/S 3s orbitals with the cation levels, with the more core-like character of the S 3s leading to a relatively low conduction band energy at the Γ point. Based on these results and previous research on electrides, approaches can be devised to control the energy levels of cation sublattices in semiconductors.

Hydride-Based Electride Material, LnH2 (Ln = La, Ce, or Y).

In view of the strong electron-donating nature of H(-) and extensive vacancy formation in metals by hydrogen insertion, a series of LnH2+x (Ln = La, Ce, or Y) compounds with fluorite-type structures were verified to be the first hydride-based electride, where itinerant electrons populating the cage are surrounded by H(-) anions. The electron transfer into the cage probably originates from Ln-cage covalent interaction. To the best of our knowledge, anion-rich electrides are extremely rare, and a key requirement for their formation is that the cage site is not occupied by lone pair electrons of the adjacent ions. In the case of LnH2, the cage site is surrounded by eight H(-) anions with isotopic electronic character caused by the lack of mixing of H p-orbital character. Notably, Ru-loaded LnH2+x electride powders synthesized by hydrogen embrittlement (Ln = La or Ce) were found to work as efficient catalysts for ammonia synthesis at ambient pressure, without showing serious signs of hydrogen poisoning. There are several possible origins of the observed high catalytic activity in the hydride promotors: the small work function of LnH2+x derived from the covalent interaction between Ln cation and the H(-) σ donor, and the formation of Ln nitride during catalytic reaction.

An anti CuO2-type metal hydride square net structure in Ln2M2As2H(x) (Ln=La or Sm, M=Ti, V, Cr, or Mn).

Using a high pressure technique and the strong donating nature of H(-), a new series of tetragonal La2Fe2Se2O3-type layered mixed-anion arsenides, Ln2M2As2H(x), was synthesized (Ln=La or Sm, M=Ti, V, Cr, or Mn; x≈3). In these compounds, an unusual M2H square net, which has anti CuO2 square net structures accompanying two As(3-) ions, is sandwiched by (LaH)2 fluorite layers. Notably, strong metal-metal bonding with a distance of 2.80 Šwas confirmed in La2Ti2As2H2.3, which has metallic properties. In fact, these compounds are situated near the boundary between salt-like ionic hydrides and transition-metal hydrides with metallic characters.

New LaMAsH(x) (M = Co, Ni, or Cu) arsenides with covalent M-H chains.

A new series of tetragonal LaPtSi-type mixed-anion arsenides, LaMAsH(x) (M = Co, Ni, or Cu), has been synthesized using high-temperature and high-pressure techniques. The crystal structure of these intermetallic compounds determined via powder neutron diffraction is composed of a 3D framework of three connected planes with the La ions filling the cavities in the structure. Each late transition-metal ion M, all of which have relatively large electronegativities, behaves like a main group element and forms a planar coordination configuration with three As ions. The trigonal-bipyramidal coordination adopted by the H in the cavity, HM2La3, is compressed along the C3 axis, and unusual M-H chains run along the x and y directions, reinforcing the covalent framework. These chains, which are unique in solids, are stabilized by covalent interactions between the M 4s and H 1s orbitals.

Hydrothermal crystal growth and structure determination of double hydroxides LiSb(OH)6, BaSn(OH)6, and SrSn(OH)6.

Colorless single crystals of LiSb(OH)6, SrSn(OH)6, and BaSn(OH)6, which are useful as precursors for the synthesis of LiSbO3, SrSnO3, and BaSnO3, were synthesized by a low-temperature hydrothermal method using a Teflon-lined autoclave at 380 K. The crystal structures were determined by single-crystal X-ray diffraction measurements. LiSb(OH)6 crystallizes in the trigonal space group P3̅1m with a = 5.3812(3)A, c = 9.8195(7)A, V = 246.25(3)A(3), Z = 2. In this layered structure, [Li2Sb(OH)6](+) and [Sb(OH)6](-) layers are alternately stacked along the c-direction. The [Li2Sb(OH)6](+) layer can be regarded as a cation-ordered CdCl2 layer. The [Sb(OH)6)](-) layer is built up from isolated [Sb(OH)6](-) octahedra, which are linked to each other via hydrogen bonding within the layer. BaSn(OH)6 and SrSn(OH)6 crystallize with monoclinic P21/n space group symmetry. The monoclinic structure possesses a CsCl-type packing of Ba(2+)/Sr(2+) cations and [Sn(OH)6](2-) anions. The [Sn(OH)6](2-) polyhedra are connected to each other through hydrogen bonding to form a three-dimensional framework. The factors that favor these hitherto unknown crystal structures are discussed using a structure map that compares various M(OH)3 and M'M″(OH)6 compounds.

Exploration of heterogeneous catalyst for molecular hydrogen ortho-para conversion.

Molecular hydrogen (H2) ortho-para conversion (O/P conversion) proceeds slowly at low temperatures accompanying a heat release. Thus, catalysts for accelerating this conversion rate are highly demanded in terms of the storage and utilization of liquid H2. The catalysts for this purpose are experimentally screened by examining a broad range of materials covering magnetic, non-magnetic, metallic, and nonmetallic oxides. The primary conclusions obtained are summarized below. (1) active materials are required to be non-metallic and to bear the cations with ionic radii smaller than the bond length of H2. (2) Metallic materials have almost no activity irrespective of with or without magnetism (3) The activity of materials belonging to (1) is largely enhanced when the constituting cation has a magnetic moment. In addition, there is a class of materials for which the activity is distinctly enhanced just upon substitution by the foreign ions.

Magnetic structure and electromagnetic properties of LnCrAsO with a ZrCuSiAs-type structure (Ln = La, Ce, Pr, and Nd).

We report the synthesis, structure, and electromagnetic properties of Cr-based layered oxyarsenides LnCrAsO (Ln = La, Ce, Pr, and Nd) with a ZrCuSiAs-type structure. All LnCrAsO samples showed metallic electronic conduction. Electron doping in LaCrAsO by Mn-substitution for the Cr sites gave rise to a metal-insulator transition. Analysis of powder neutron diffraction data revealed that LaCrAsO had G-type antiferromagnetic (AFM) ordering, i.e., a checkerboard-type AFM ordering in the CrAs plane and antiparallel spin coupling between the adjacent CrAs planes, at 300 K with a large spin moment of 1.57 µB along the c axis. The magnetic susceptibility of LaCrAsO was very small (on the order of 10(-3) emu/mol) and showed a broad hump at ∼550 K. First-principles density functional theory calculations of LaCrAsO explained its crystal structure and metallic nature well, but could not replicate the antiparallel spin coupling between the CrAs layers. The electronic structure of LaCrAsO is discussed with regard to those of related compounds LaFeAsO and LaMnAsO.

Ammonia Cracking Catalyzed by Ni Nanoparticles Confined in the Framework of CeO2 Support.

For the extraction of hydrogen from ammonia at low temperatures, we investigated Ni-based catalysts fabricated by the thermal decomposition of RNi5 intermetallics (R = Ce or Y). The interconnected microstructure formed via phase separation between the Ni catalyst and the resulting oxide support was observed to evolve via low-temperature thermal decomposition of RNi5. The resulting Ni/CeO2 nanocomposite exhibited superior catalytic activity of ∼25% at 400 °C for NH3 cracking. The high catalytic activity was attributed to the interlocking of Ni nanoparticles with the CeO2 framework. The growth of Ni nanoparticles was prevented by this interconnected microstructure, in which the Ni nanoparticles incorporated nitrogen owing to the size effect, whereas Ni does not commonly form nitrides. To the best of our knowledge, this is a unique example of a microstructure that enhances catalytic NH3 cracking.

Superconductivity in LaT(M)BN and La3T(M2)B2N3 (T(M) = transition metal) synthesized under high pressure.

Various layered boronitrides (LaN)(n)(T(M2)B(2)) (T(M) = transition metal; n = 2, 3) have been prepared using a high-pressure synthesis technique in which an inverse α-PbO-type T(M2)B(2) layer is separated by two or three rock salt-type LaN layers and these layers are connected through linear (BN) units. The electronic states of the distinguishing (BN) unit and intermediate rock salt-type LaN layer are discussed on the basis of density functional theory calculations. Bulk superconductivity has been found in LaNiBN (T(c) ≈ 4.1 K), CaNiBN (T(c) ≈ 2.2 K), and LaPtBN (T(c) ≈ 6.7 K), where the Fermi level E(F) is located in the bands composed of the T(M)(d)-B(2p) antibonding state and the main T(M)(d) band resides well below E(F). The non-superconductive T(M)-based compounds exhibit Pauli paramagnetic behavior, in which the highly itinerant nature of the electrons caused by strong T(M)(d)-B(2p) covalent bonding suppresses the long-range magnetic ordering.

Superconductivity in defective pyrite-type iridium chalcogenides Ir(x)Ch2 Ch = Se and Te.

We report superconductivity in defective pyrite-type iridium chalcogenides Ir(x)Ch2 (Ch = Se and Te). Maximum values of T(c) of 6.4 K for Ir(0.91)Se(2) and 4.7 K for Ir(0.93)Te(2) were observed. It was found that Ir(0.75)Ch(2) (Ir(3)Ch(8)) is close to the boundary between metallic and insulating states and Ir(x)Ch(2) systems undergo nonmetal to metal transitions as x increases. On the basis of density functional theory calculations and the observed large variation in the Ch-Ch distance with x, we suggest that Ir(0.75)Ch(2) (Ir(3)Ch(8)) is the parent compound for the present superconductors.

YdfH identified as a repressor of rspA by the use of reduced genome Escherichia coli MGF-01.

We have reported the construction of 1 Mb reduced genome Escherichia coli MGF-01 by a 28-step operation. This time, transcriptome analysis of MGF-01 was performed. Although the transcriptome profiles of the exponential phase in parental strain W3110red were well-conserved in MGF-01, the rspAB operon was highly expressed. A LacZ reporter assay of a series of stepwise deletion strains prepared in the course of MGF-01 construction indicated that rspA was highly expressed after the 5th step. Further analysis indicated that Δ29, one of the deleted regions at the 5th step, relates to an increase in rspA expression, and that transcriptional regulator ydfH, in the Δ29 region, is responsible for the expression of rspA, gel shift assay indicated that YdfH bound directly to the upstream region of rspA. Based on these results, it was concluded that YdfH is a transcriptional repressor of the rspAB operon.