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The electronic and thermoelectric properties of Bi2Te3, PbBi2Te4 and PbBi4Te7 were examined on the basis of density functional theory (DFT) calculations and thermoelectric transport property measurements. The layered phase PbBi4Te7 is composed of the slabs forming the layered phases Bi2Te3 and PbBi2Te4. The electronic structure of PbBi4Te7 around the valence band maximum and conduction band minimum exhibits those of Bi2Te3 and PbBi2Te4. The band gap of PbBi4Te7 lies in between those of Bi2Te3 and PbBi2Te4, and the density of states of PbBi4Te7 is well approximated by the sum of those of Bi2Te3 and PbBi2Te4. In terms of the carrier concentration, the carrier mobility, the carrier lifetime, the electrical conductivity normalized to the carrier lifetime, and the effective mass, the layered phases Bi2Te3, PbBi4Te7 and PbBi2Te4 form a group of thermoelectrics, which have the structures composed of several different slabs and whose thermoelectric properties are approximated by the average of those of the constituent slabs. We propose to use the term “LEGO thermoelectrics” to describe such a family of thermoelectric materials that operate in a desired temperature range and possess predictable thermoelectric properties.

ZnO twin-prisms were prepared by a simple solvothermal process with glutamic acid as surface modification agent in ethanol. Compared with the twin-cones that were obtained when glutamic acid was absent, the ZnO twin-prisms have optimized crystallinity with high symmetry, sharp crystal edges and few defects. Probable reaction mechanism between ZnO and glutamic acid was proposed based on our experimental analysis. Then it was verified by a series of comparison experiments by employing glycine, acetic acid and ethylamine as surface modification agents. Our results indicate that both alkaline and acidic groups play an important role on the formation of ZnO twin-prisms, and when either of them was absent, twin-prism structures cannot be obtained. The photoluminescence properties of as-prepared ZnO twin-prisms and twin-cones were also studied.

The multiferroic langasite Ba3NbFe3Si2O14, crystallizing in a noncentrosymetric space group, has sheets of Fe3+ ions parallel to the ab plane. It adopts a chiral magnetic order below TN = 26 K that has a superstructure with propagation vector (0, 0, ∼1/7). The spin frustration causing this magnetic structure of Ba3NbFe3Si2O14 was examined by evaluating its spin exchange interactions on the basis of density functional calculations and also by calculating its magnetic dipole−dipole interactions. The contribution of the chiral magnetic structure to the ferroelectric polarization of Ba3NbFe3Si2O14 below TN was estimated by Berry phase calculations. The spin exchanges of Ba3NbFe3Si2O14 are frustrated in each //ab sheet and between adjacent sheets of Fe3+ ions. The helical spin rotation along the c axis occurs to minimize the intersheet spin frustration as well as the intersheet magnetic dipole−dipole interactions. The ferroelectric polarization of Ba3NbFe3Si2O14 estimated from calculations is in good agreement...

The origin of the collinear antiferromagnetic magnetic structure of Ni(3)TeO(6) below 52 K was analyzed by calculating its spin exchanges on the basis of density functional calculations, and the cause for the parallelc-spin orientation found for this magnetic structure by calculating the spin-orbit coupling and magnetic dipole-dipole interaction energies. The calculated exchanges correctly predict the observed magnetic structure below 52 K, and lead practically to no spin frustration. The perpendicularc- and parallelc-spin orientations are predicted by the spin-orbit coupling and the magnetic dipole-dipole interactions, respectively. However, the magnetic dipole-dipole interactions are stronger than the spin-orbit coupling interactions, and hence are responsible for the spin orientation observed for Ni(3)TeO(6).

Polycrystalline samples of AgCuF 3 , isostructural with NaCuF 3 , were synthesized by solid state reaction and characterized by powder X-ray diffraction. The magnetic properties of AgCuF 3 and NaCuF 3 were examined by measuring their magnetic susceptibilities and evaluating their spin exchange interactions. The three-dimensional CuF 3 network of corner-sharing CuF 6 octahedra present in AgCuF 3 and NaCuF 3 shows a cooperative Jahn–Teller distortion such that their magnetic susceptibilities above 50 K are well described by an S = 1/2 Heisenberg uniform antiferromagnetic chain model with average spin exchange of J / k B ≈ −300 and −180 K, respectively. The relative strengths of these interactions are well reproduced by spin dimer analysis based on tight-binding calculations, but not by mapping analysis based on first principles density functional calculations.

The spin exchange interactions of VO(CH3CO2)2 and VO(OCH2CH2O) were investigated by performing spin dimer analysis based on tight binding calculations and mapping analysis based on first principles density functional theory calculations. In agreement with experiment, both analyses show that the magnetic properties of VO(CH3CO2)2 and VO(OCH2CH2O) are best described by uniform antiferromagnetic one-dimensional chain and isolated antiferromagnetic dimer models, respectively. Our study shows that the nearest-neighbor spin exchange in the one-dimensional chains of VO5 square pyramids in VO(CH3CO2)2 is mediated by the C 2pπ orbital of the carboxylate group, and that the cis spin dimers of VO(OCH2CH2O) provide strong antiferromagnetic spin exchange than do the trans spin dimers of VO(OCH2CH2O).

The two cobalt hexagonal perovskites 6H-Ba(6)Co(6)F(0.93)O(16) and 10H-Ba(5)Co(5)F(0.77)O(12.88) were prepared, and their structures were examined by X-ray and neutron diffraction and by (19)F solid state NMR spectroscopy. The magnetic and transport properties of these compounds were probed by magnetic susceptibility and electrical resistivity measurements, and their electronic structures by density functional and tight-binding calculations. The [BaOF(1-x)] layers of these compounds create corner-sharing tetrahedral Co(2)O(7) dimers at the interface between their face-sharing octahedral oligomers. Our density functional calculations leads to an unambiguous charge distribution model, which assigns high-spin Co(3+) ions for the tetrahedral sites and low-spin Co(3+)/Co(4+) ions for the octahedral sites, and this model should be valid for the parent BaCoO(3-delta) and the related oxychlorides and oxybromides as well. The F(-) vacancies in the [BaOF(1-x)] layers cause a strong distortion in the tetrahedral dimer Co(2)O(7), which in turn affects the spin orientation of the high-spin Co(3+) ions of the CoO(4) tetrahedra, i.e., parallel to the c-direction in Ba(6)Co(6)F(1-x)O(16-delta) but perpendicular to the c-direction in Ba(5)Co(5)F(1-x)O(13-delta). This difference in the spin orientations is related to the d-states of the distorted CoO(4) tetrahedra with high-spin Co(3+) (d(6)) ion on the basis of tight binding calculations and spin-orbit coupling as perturbation.

materials is based on perovskites, ABO3, with two different cations A and B (for example A 2+ and B 4+ or A 3+ and B 3+ ), in which corner-sharing BO6 octahedra form the three-dimen- sional lattice with every B8 cube containing one A cation. An ideal cubic perovskite, in which the B-OB bonds are linear with A located at the center of each B8 cube (thus forming a AO12 polyhedron), is expected when the tolerance factor t = (rO + rA)/ ffiffiffi 2 p (r O+rB) is unity (rA and rB are the ionic radii of the A and B cations, respectively, with rO as that of the O 2� anion). In most cases, the A cations are small, so that t < 1 and the AO bonds are too long to maintain the ideal cubic structure. Consequently, the A cation moves away from the center of the B8 cube, which is accompanied by the bending of the B-O-B bonds and the rotation of the BO6 octahedra to form a lower-coordinate AOn polyhedron (n < 12) with short AO bonds. The distortion of the ideal cubic perovskite toward a non-centrosymmetric FE structure requires another local instability apart from t < 1, namely, the second-order Jahn-Teller (SOJT) instability (4-6) of the A-site and/or B-site

First principles density functional calculations were carried out to probe the oxidation states of the transition-metal and alkaline-earth elements in the Cr5B3-type compounds AE5T3 consisting of T2 dimers and isolated T atoms (i.e., Ca5Au3, Ca5Ag3, Ca5Hg3, Sr5Cd3, and Ca5Zn3). The electronic structures of all these AE5T3 compounds are best described as [(AE2+)5(T–T)4–(T2–)]+4e–. In the covalent bonding of the AE2+ ions with the transition metal anions T2–, the (n–1)d orbitals of AE2+ contribute more than the ns and np orbitals of AE2+.

The structural and magnetic properties of anhydrous (black) dioptase, CuSiO3, were investigated by carrying out single-crystal X-ray diffraction, specific heat, and magnetic susceptibility measurements as well as by performing spin dimer analysis based on extended Huckel tight-binding calculations. Our spin dimer analysis indicates that black dioptase is a S = 1/2 uniform antiferromagnetic chain system with the interchain spin exchange weaker than the intrachain exchange by three orders of magnitude. Specific heat and magnetic susceptibility measurements show that the intrachain exchange is –174(2) K, and the interchain exchange is of the order of ~2 K. They lead to long-range magnetic ordering at about 5 K as evidenced by a broad anomaly in the specific heat.

The visible-light responsive photocatalyst BiVO4 was synthesized, and its photocatalytic reduction of CO2 in water was examined. Our study shows the selective formation of ethanol under the condition of high intensity visible-light irradiation, and suggests that intense irradiation generates a large number of C1 intermediate species anchored on the surface of BiVO4, which dimerize to form ethanol. For the photocatalytic reduction of CO2 into ethanol, monoclinic BiVO4 is more efficient than tetragonal BiVO4.

A new composite photocatalyst Ag/AgBr/WO(3).H(2)O was synthesized by reacting Ag(8)W(4)O(16) with HBr and then reducing some Ag(+) ions in the surface region of AgBr particles to Ag nanoparticles via the light-induced chemical reduction. Ag nanoparticles are formed from AgBr by the light-induced chemical reduction reaction. The Ag/AgBr particles are on the surface of WO(3).H(2)O and have irregular shapes with sizes varying between 63 and 442 nm. WO(3).H(2)O appears as flakes about 31 nm thick and 157-474 nm wide. The as-grown Ag/AgBr/WO(3).H(2)O sample shows strong absorption in the visible region because of the plasmon resonance of Ag nanoparticles in Ag/AgBr/WO(3).H(2)O. The ability of this compound to destroy E. coli and oxidize methylic orange under visible light was compared with those of other reference photocatalysts. Ag/AgBr/WO(3).H(2)O is a highly efficient photocatalyst under visible light. The Ag/AgBr/WO(3).H(2)O samples recovered from repeated photooxidation experiments are almost identical to the as-prepared samples, proving the stability of Ag/AgBr/WO(3).H(2)O sample.

The ferromagnetic and antiferromagnetic states of anatase and rutile TiO 2 doped with N atoms at oxygen sites were investigated by density functional theory calculations for a number of model N-doped TiO 2 structures. The each N dopant at an O site exists as an N 2− ion with net spin moment of 1.0 μ B . In general, the spin exchange coupling between the spin moments of two N dopants is strong when the two dopants are coordinated to a common Ti atom, and whether the coupling between the two N atoms is ferromagnetic or antiferromagnetic in such a case depends on the ∠N–Ti–N angle.

We investigated the optical properties of (NBu{sub 4}){sub 3}[Ni(NCS){sub 5}], a pentacoordinate Ni compound, and compared the results with the more traditional hexacoordinate analogue (NEt{sub 4}){sub 4}[Ni(NCS){sub 6}]. On the basis of our complementary electronic structure calculations, the color properties of this high spin complex can be understood in terms of excitations between strongly hybridized orbitals with significant Ni d and ligand character. Variable temperature vibrational studies show mode softening with decreasing temperature and splitting near 200 K, trends that we attribute to improved low temperature intermolecular interactions and a weak structural phase transition, respectively.

First-principles density functional calculations were carried out to examine the electronic and magnetic properties of rare-earth iron borate TbFe3(BO3)4. The spin exchange interactions between the Fe3+ (d5, S = 5/2) ions and the preferred orientation of the Tb3+ (f8) spins were evaluated, and the ferroelectric polarization of TbFe3(BO3)4 was calculated. In agreement with experiment, our calculations predict that the spin exchange between the Fe3+ spins is ferromagnetic within each //ab sheet of Fe3+ ions but antiferromagnetic between adjacent //ab sheets of Fe3+ ions, whereas the spin exchange between the Fe3+ and Tb3+ ions within each //ab sheet of Fe3+ and Tb3+ ions is antiferromagnetic. The Tb3+ (f8) ions is found to possess an electron configuration responsible for uniaxial magnetism, hence orienting the Tb3+ spins along the c-direction and leading to the highly anisotropic magnetic susceptibility. The ferroelectric polarization of TbFe3(BO3)4 is largely due to the absence of inversion symmetry of th...

Three Cu2+-containing coordination polymers were synthesized and characterized by experimental (X-ray diffraction, magnetic susceptibility, pulsed-field magnetization, heat capacity, and muon-spin relaxation) and electronic structure studies (quantum Monte Carlo simulations and density functional theory calculations). [Cu(HF2)(pyz)2]SbF6 (pyz = pyrazine) (1a), [Cu2F(HF)(HF2)(pyz)4](SbF6)2 (1b), and [CuAg(H3F4)(pyz)5](SbF6)2 (2) crystallize in either tetragonal or orthorhombic space groups; their structures consist of 2D square layers of [M(pyz)2]n+ that are linked in the third dimension by either HF2− (1a and 1b) or H3F4− (2). The resulting 3D frameworks contain charge-balancing SbF6− anions in every void. Compound 1b is a defective polymorph of 1a, with the difference being that 50% of the HF2− links are broken in the former, which leads to a cooperative Jahn−Teller distortion and dx2−y2 orbital ordering. Magnetic data for 1a and 1b reveal broad maxima in χ at 12.5 and 2.6 K and long-range magnetic order...

The structural and electronic properties of two possible substitutional carbon-doped structures of anatase and rutile TiO2 [i.e., C for O (C@O)- and C for Ti (C@Ti)-doped TiO2] were studied by performing first-principle density functional theory calculations. In C-doped TiO2 with C@O, the band gap changes slightly, but the doped carbon introduces spin-polarized gap states of C 2p orbital in character. Thus, the associated electron excitations among the valence band, the conduction band, and the gap states explain the various visible-light absorption thresholds observed for C anion-doped TiO2. For C-doped anatase and rutile TiO2 with C@Ti, the doped C atom does not induce spin-polarized states. For C-doped anatase TiO2 with C@Ti, the optical absorption energy is reduced by about 0.18 eV, and the C dopant forms a linear O−C−O unit with short C−O distance resembling carbon dioxide, which is consistent with experiment. In C-doped rutile TiO2 with C@Ti, C-doping reduces the optical absorption energy by about 0...

The structural, electronic, and magnetic properties of the new linear chain coordination polymer CuF 2(H 20) 2(pyz) (pyz = pyrazine) were determined by single crystal X-ray diffraction at various temperatures, SQUID magnetometry, pulsed-field magnetization, ESR, muon-spin relaxation (uSR), and electronic structure calculations. Each Cu 2+ ion of CuF 2(H 2O) 2(pyz) is located at a distorted CuF 2O 2N 2octahedron with axial elongation along the Cu-N bonds. These octahedra are tethered together by strong F. . . H-O hydrogen bonds to yield two-dimensional (2D) square nets in the bc-plane that are linked along the α-direction by pyrazine linkages. Measurements of the g-factor by ESR along with first principles density functional theory electronic structure calculations show that the magnetic orbital of the Cu 2+ ion lies in the CUF 2O 2 plane thus forming a 2D antiferromagnetic square lattice. A broad maximum observed in χ(T) at 10 K indicates a modest spin exchange interaction through the Cu-F. . . H-O-Cu supersuperexchange paths, and a theoretical fit of χ(T) to a 2D square model gives J 2D LK B= -5.58(1) K (in the convention where J rather than 2J is used for spin exchange). At lower temperatures, χ(T) shows a sharp peak at ̃2.6 K, which signals a transition to a long-range magnetic ordering as confirmed by coherent precession of implanted muons. Isothermal M{B) measurements made at 0.5 K on an aligned single crystal reveal magnetic saturation, M sat, at 28.8 T (Blla) while a higher field of 33.1 T is required to saturate the spins when B is applied perpendicular to the α-axis thus showing clear anisotropy in these orientations. The presence of strong hydrogen bonds in CuF 2(H 20)2(ρyz) causes the chains to adopt a tilted packing arrangement, thus leading to a novel ground-state likely characterized by spin-canting within the 2D layers and a markedly increased critical temperature relative to the well-known Cu(NO 3) 2(pyz) polymer chain compound. © 2008 American Chemical Society.

First-principles density functional theory (DFT) electronic structure calculations were carried out for model halogen-doped anatase TiO2 structures to evaluate the effect of halogen doping on the band edges and the photocatalytic activity of TiO2. The model structures of X-doped TiO2 were constructed by using the 48-atom 2 × 2 × 1 supercell of anatase TiO2 with one O or one Ti atom replaced with X (=F, Cl, Br, I). The unit cell parameters and the atom positions of the resulting X-doped TiO2 with X at an O site (X@O) and that with X at a Ti site (X@Ti) were optimized by performing first-principles DFT calculations. On the basis of the optimized structures of X-doped TiO2 with X@O and X@Ti, the defect formation energies and the plots of the density of states were calculated to analyze the band edges, the band gap states, and the preferred doping sites. Our work shows that the doping becomes more difficult in the order F < Cl < Br < I for X-doped TiO2 with X@O, while the doping becomes less difficult in the ...

The crystal structure of copper carbodiimide, CuNCN, was determined from neutron diffraction data at room temperature and at 4 K, and the electrical resistivity, specific heat, and magnetic susceptibility measurements were carried out. The spin exchange interactions of CuNCN were evaluated by performing first-principles density functional theory electronic structure calculations. CuNCN is a semiconductor containing Jahn−Teller distorted CuN6 octahedra around the divalent copper ions, and the material shows a very small and almost temperature-independent magnetic susceptibility. Our electronic structure calculations evidence that the spin exchange interactions of CuNCN are dominated by two antiferromagnetic spin exchange paths leading to a triangular lattice antiferromagnet within the ab plane. Because the coupling between the layers (along the c axis) is small, CuNCN may be regarded a two-dimensional S = 1/2 frustrated triangular Heisenberg quantum antiferromagnet.

The quaternary magnetic oxide Bi4Cu3V2O14 consists of Cu4O8 triple chains made up of corner-sharing CuO4 square planes. To determine its spin-lattice, the spin exchange interactions of Bi4Cu3V2O14 were evaluated by performing a spin dimer analysis based on tight-binding calculations and a mapping analysis based on first principles density functional theory calculations. Both calculations show that the spin-lattice of Bi4Cu3V2O14 is not an antiferromagnetically coupled diamond chain, which results from an idealized view of the structure of the Cu4O8 triple chain and a neglect of super-superexchange interactions. The correct spin-lattice is an antiferromagnetic chain made up of antiferromagnetic linear trimers coupled through their midpoints via super-superexchange interaction, which predicts that Bi4Cu3V2O14 has an antiferromagnetic spin ground state and has no spin frustration, both in agreement with experiment.

A brief review is given for those extended solids of transition metal compounds in which their transition metal atoms are best described as existing as anions. Analyses of the electronic structures of metal-rich fluorides and oxides containing octahedral metallo -complexes [MIn 6− x Sn x ] (M = Fe, Ni, Ru, Os, Ir and Pt) indicate that their transition metal atoms M are present as anions with the valence electron configuration ( n + 1)s 2 n d 10 . In compounds RE 2 M 2 In (RE = rare earth element, M = Pt, Cu and Au), Ca 5 Au 4 , Ca 3 Hg 2 and Ca 5 M 3 (M = Cu, Au, Zn, Cd and Hg), the transition metal atoms exist as dimeric Zintl anions with the valence electron configuration ( n + 1)s 2 n d 10 ( n + 1)p 1 . Consequently, the frontier orbitals of these compounds are not described by the transition metal n d orbitals, but by the transition metal ( n + 1)p orbitals. A similar situation is found for most 18-electron half-Heusler compounds (e.g., ScAuSn), for which the valence electron configuration of the transition metal is given by ( n + 1)s 2 n d 10 ( n + 1)p 2 .

The chemical bonding of the M2 dimers (M = Ag, Au, Hg) present in Yb3Ag2, Ca5Au4 and Ca3Hg2 was examined on the basis of first principles electronic band structure calculations. In these compounds, the 6s- and 5d-block bands of M are completely filled while the frontier levels of M are given by partially filled 6p-block bands such that the transition metal atoms M are best described as anions with electron configuration (5d)10(6s)2(6p)1. Thus, the M2 dimers (M = Ag, Au, Hg) of Yb3Ag2, Ca5Au4 and Ca3Hg2 are present as [Ag−Ag]4−, [Au−Au]4−, and [Hg−Hg]2− Zintl-anions, respectively, in these compounds in which the M2 dimers have a single bond formed by the pσ−pσ interaction between the 5p and 6p orbitals of M atoms. The anions of late transition metal elements are different from those of late main group elements in their tendency for covalent bond formation.

A self-assembled monolayer of 2,2'-bipyridine (22BPY) molecules on Au(111) underwent a structural phase transition when the polarity of a bias voltage was switched in scanning tunneling microscopy (STM) experiments. The nature of two bright spots representing each 22BPY molecule on Au(lll) in the high-resolution STM images was identified by calculating the partial density plots for a monolayer of 22BPY molecules adsorbed on Au(111) using tight-binding electronic structure calculations. The stacking pattern of the chains of 22BPY molecules on Au(111) was explained by examining the intermolecular interactions between the 22BPY molecules based on first principles electronic structure calculations for a 22BPY dimer, (22BPY) 2 . The structural instability of the 22BPY molecule arrangement caused by a change in the bias voltage switch was investigated by estimating the adsorbate-surface interaction energy using a point-charge approximation for Au(111).

NH4CuPO4·H2O is a spin-gapped compound that has been described in terms of an isolated antiferromagnetic spin dimer model. To explore the origin of this spin gap, we examined the spin exchange interactions of NH4CuPO4·H2O by performing qualitative spin dimer analysis based on extended Huckel tight binding calculations and also by carrying out quantitative mapping analysis based on first principles density functional theory electronic band structure calculations. Our study indicates that, to a first approximation, the magnetic properties of NH4CuPO4·H2O should be described by an antiferromagnetic and ferromagnetic alternating chain.

The abilities of the (HPO3)2– and (SeO3)2– anions as structure building units and as spin exchange paths between magnetic ions were investigated by preparing and analyzing the isostructural Fe2(SeO3)3 and Fe2(HPO3)3. In both compounds, the face-sharing Fe2O9 dimers are interconnected into chains by the (HPO3)2– and (SeO3)2– anions. The (HPO3)2– is the structural counterpart of the Se electron lone pair of (SeO3)2– due to the weak hydride character of the terminal hydrogen. However, they differ considerably as spin exchange paths between magnetic cations. Both compounds exhibit an effective magnetic dimer behavior, unexpectedly arising from the interdimer Fe—O···O—Fe exchange along the chain, but weaker in Fe2(HPO3)3 by a factor of ∼3. It is consistent with the general tendencies of the phosphite anions to act as a weak magnetic mediator, which is caused by the through-bond effect of the P3+ ion in the Fe—O···P3+···O—Fe exchange path, much weaker than in the selenite phase in absence of P3+d contribution. ...

The recent report of superconductivity under high pressure at the record transition temperature of Tc=203K in sulfur hydride has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms can neither account for the observed values of Tc nor the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope effect. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active, Comment: 11 pages, 5 figures

The relationships among the pressure P, volume V, and temperature T of solid-state materials are described by their equations of state (EOSs), which are often derived from the consideration of the finite-strain energy or the interatomic potential.1-3 These EOSs consist of typically three parameters to determine from experimental P-V-T data by fitting analyses. In the empirical approach to EOSs, one either refines such fitting parameters or improves the mathematical functions3-5 to better simulate the experimental data. Despite over seven decades of studies on EOSs, none has been found to be accurate for all types of solids over the whole temperature and pressure ranges studied experimentally.3,6,7 Here we show that the simple empirical EOS, P = {\alpha}1(PV) + {\alpha}2(PV)2 + {\alpha}3(PV)3, in which the pressure P is indirectly related to the volume V through a cubic polynomial of the energy term PV with three fitting parameters {\alpha}1 - {\alpha}3, provides accurate descriptions for the P-vs-V data of condensed matter in a wide region of pressure studied experimentally even in the presence of phase transitions, Comment: 59 pages; 3 tables and 2 figures in the main text; numerous tables and figures in the supporting information; For further information please see http://www.nature.com/srep/journal-policies/editorial-policies/#confidentiality

The spin lattice model for the spin-gapped layered magnetic solids Na3Cu2SbO6 and Na2Cu2TeO6 was examined by evaluating the three spin exchange interactions of their Cu2MO6 (M = Sb, Te) layers in terms of spin dimer analysis based on extended Hückel tight binding calculations and mapping analysis based on first principles density functional theory electronic band structure calculations. For both compounds, our calculations show that the two strongest spin exchange interactions, that is, the Cu-O...O-Cu super-superexchange (J2) and the Cu-O-Cu superexchange (J1) interactions, form alternating chains that interact weakly through the Cu-O-Cu superexchange (J3) interactions. The dominant one of the three spin exchange interactions is J2, and it is antiferromagnetic in agreement with the fact that both of the compounds are spin gapped. For Na3Cu2SbO6 and Na2Cu2TeO6, the superexchange J1 is calculated to be ferromagnetic, hence, leading to the alternating chain model in which antiferromagnetic and ferromagnetic spin exchange interactions alternate. This picture does not agree with the recent experimental analysis, which showed that the temperature-dependent magnetic susceptibilities of both compounds should be described by the alternating chain model in which two antiferromagnetic spin exchange interactions of different strengths alternate.

18-electron compounds REML (RE = rare earth metal; M = Cu, Ag, Au; L = Ge, Sn) can adopt either the stuffed graphite-like (P63mc) or the stuffed diamond-like () structure. To understand why one structure is favored over the other, we carried out density functional theory electronic structure calculations for a number of REAuSn compounds. The stuffed graphite-like and stuffed diamond-like structures of an 18-electron compound REAuSn are quite similar in their electronic structures with the Au atoms best described as existing as anions. The diamond-like REML becomes possible only when the RE3+ ion is small and the M-L bond is long.

International audience; A new ternary vanadate KMnVO4 was prepared by a solid-state reaction and was shown to be a new type of ordered oxygen-deficient perovskite ABO3 - with = 1/3. Its formula can be rewritten as (K2,Mn)[Mn,V2]O8 1. An ordered distribution of potassium and manganese atoms in the A site and of vanadium and manganese atoms in the B site is observed. The manganese atoms are in distorted octahedral and tetrahedral sites, whereas all of the vanadium atoms form VO43- tetrahedra. This oxide contains four different types of high-spin Mn2+ ions in equal number. Magnetic susceptibility and specific heat measurements as well as spin dimer analysis show that substantial antiferromagnetic spin-exchange interactions occur primarily among three of the four different types of Mn2+ ions, and the fourth Mn2+ ion remains paramagnetic down to 2 K.

Spin dimer analysis was carried out for the magnetic oxides of V4+ (d1) ions, A2V3O9 (A = Ba, Sr) and η-Na9V14O35, to account for their magnetic structures. After identifying the V(Oeq)4 square planes containing the magnetic orbitals of the V4+ (d1) ions, we analyzed the relative strengths of the various V–Oeq–V and V–Oeq⋯Oeq–V spin exchange interactions. The V–Oeq⋯Oeq–V spin exchange interactions mediated by Oeq–V5+–Oeq bridges are found to be crucial in determining the magnetic structures of A2V3O9 (A = Ba, Sr) and η-Na9V14O35. Our analysis suggests that η-Na9V14O35 should have two different spin gaps.

IrIn7GeO8 = [IrIn6](GeO4)(InO4) and Compounds of the Solid Solution Series [IrIn6](Ge1+xIn1−4x/3O8) (0 ≤ x ≤ 0.75): First Oxides containing [IrIn6] Octahedra The low valent indiumoxides IrIn7GeO8 = [IrIn6](GeO4)(InO4) and [IrIn6](Ge1+xIn1−4x/3O8) (0 x ≤ 0.75) are formed by heating intimate mixtures of Ir, In, In2O3 and GeO2 in corundum crucibles under an atmosphere of argon (1420 K, 70 h). The compounds are black and semiconducting. X-ray powder diffraction patterns can be indexed on the basis of a face centered cubic unit cell with lattice parameters ranging from a = 1012.3(1) pm (x = 0) to a = 1007.3(1) pm (x = 0.75). Characteristic building units in [IrIn6](Ge1+xIn1−4x/3O8) are isolated [IrIn6]9+ octahedra with short Ir-In distances of 253.5 pm, which are linked via [GeO4]4− and [InO4]5− tetrahedra to a three dimensional framework. Starting from IrIn7GeO8 = [IrIn6](GeO4)(InO4), the isoelectronic substitution of 4 In3+ ions by 3 Ge4+ ions and one Ge-vacancy leads to the formation of a solid solution series [IrIn6](GeO4)1+x(O4)x/3(InO4)1−4x/3, which shows a slight decrease in the cubic lattice parameter with increasing x. According to Rietveld refinements the structure of [IrIn6](GeO4)(InO4) exhibits a statistical distribution of the tetrahedrally coordinated Ge and In atoms (, R(prof.) = 4.4 %, R(int.) = 2.5 %). The crystal and electronic structures of [IrIn6](GeO4)(InO4) are discussed on the basis of first principles electronic structure calculations.

The electronic structures of the new organic conducting salts, the β'- and β''-phases of (BEDT-TTF)2[(IBr2)0.2(BrICl)0.1(ICl2)0.7], were examined by calculating their electronic band structures, Fermi surfaces and HOMO-HOMO interaction energies using the extended Huckel tight binding method. On the basis of these calculations, we probed why the β'-phase is semiconducting while the β''-phase is metallic.

Using first principles density functional theory (DFT) calculations based on the full-potential linearized augmented plane wave method (LAPW), we investigated the electronic and magnetic structures for the ferromagnetic and antiferromagnetic states of La2MnNiO6 and analyzed the site-projected density of states and electronic dispersion curves. Our calculations show that the ground state of La2MnNiO6 is ferromagnetic insulating with the magnetization in agreement with Hund's first rule and experimental findings.

The Sr and Fe codoped double perovskites PrBaCo2O5.5+δ (PrBCO) thin films of Pr(Ba0.5Sr0.5)(Co1.5Fe0.5)O5.5+δ (PBSCFO) were epitaxially grown for chemical catalytic studies. The resistance behavior of PBSCFO epitaxial films was monitored under the switching flow of reducing and oxidizing gases as a function of the gas flow time, t, using an electrical conductivity relaxation (ECR) experimental setup. The R(t) vs t relationships determined at various temperatures show the occurrence of two oxidation processes, Co(2+)/Co(3+) ↔ Co(3+) and Co(3+) ↔ Co(3+)/Co(4+). Mathematical fitting of the observed R(t) vs t relationships was carried out using Fick's second law for one-dimensional diffusion of charge carriers to derive the diffusivity D(T) and τ(T) for the two processes at various temperatures, T. The D(T) vs T relationships were analyzed in terms of the Arrhenius relationship to find the activation energies Ea for each process. Oscillations in the dR(t)/dt plots, observed under oxidation reactions, were discussed in terms of a layer-by-layer oxygen vacancy exchange diffusion mechanism. Our work suggests that thin films of LnBCO (Ln = lanthanide) with their A and B sites doped as in PBSCFO are excellent candidates for the development of low or intermediate temperature energy conversion devices and gas sensor applications.

The stability of both the pure and fluorine (F)-adsorbed surface of TiO2 is examined on the basis of density functional calculations. For pure surfaces, both the beneficial local geometric structures and local potential strengthen the Ti-O binding in (101), rendering it the most stable surface. For F-adsorbed surfaces, F-adsorption significantly weakens the Ti-O bonds in (101) but strengthens them in (001), so that (001) becomes more stable than (101) for the F-adsorbed surfaces. On the basis of this observation, we further show that the n-type doping in TiO2 can significantly decrease the ability of F-adsorption in switching the relative stability of the two surfaces. The present work not only provides new insights into the physical and chemical properties about both pure and F-adsorbed surfaces of TiO2 and conclusively explains related experimental results but also suggests viable ways to prepare TiO2 samples with a high percentage of (001).

Single crystals of the title compound are prepared by reaction of MnCl2 and U3O8 in a CsCl flux (alumina crucible, 900 °C, 9 h, 40% yield).

In the search for photocatalysts that can directly utilize near-IR (NIR) light, we investigated three oxides Cu3(OH)4SO4 (antlerite), Cu4(OH)6SO4, and Cu2(OH)3Cl by photodecomposing 2,4-dichlorophenol over them under NIR irradiation and by comparing their electronic structures with that of the known NIR photocatalyst Cu2(OH)PO4. Both Cu3(OH)4SO4 and Cu4(OH)6SO4 are NIR photocatalysts, but Cu2(OH)3Cl is not. Thus, in addition to the presence of two different CuOm and Cu'On polyhedra linked with Cu-O-Cu' bridges, the presence of acceptor groups (e.g., SO4, PO4) linked to the metal oxygen polyhedra is necessary for NIR photocatalysts.

By means of density functional theory calculations, we predict that several two dimensional AB binary monolayers, where A and B atoms belong to group IV or III-V, are ferroelectric. Dipoles arise from the buckled structure, where the A and B ions are located on the sites of a bipartite corrugated honeycomb lattice with trigonal symmetry. We discuss the emerging valley-dependent properties and the coupling of spin and valley physics, which arise from the loss of inversion symmetry, and explore the interplay between ferroelectricity and Rashba spin-spitting phenomena. We show that valley-related properties originate mainly from the binary nature of AB monolayers, while the Rashba spin-texture developing around valleys is fully controllable and switchable by reversing the ferroelectric polarization.

Boron-doped monoclinic and tetragonal phases of BiVO