Structural and thermochemical chemisorption of CO2 on Li(4+x)(Si(1-x)Al(x))O4 and Li(4-x)(Si(1-x)V(x))O4 solid solutions

Different Li(4)SiO(4) solid solutions containing aluminum (Li(4+x)(Si(1-x)Al(x))O(4)) or vanadium (Li(4-x)(Si(1-x)V(x))O(4)) were prepared by solid state reactions. Samples were characterized by X-ray diffraction and solid state nuclear magnetic resonance. Then, samples were tested as CO(2) captors. Characterization results show that both, aluminum and vanadium ions, occupy silicon sites into the Li(4)SiO(4) lattice. Thus, the dissolution of aluminum is compensated by Li(1+) interstitials, while the dissolution of vanadium leads to lithium vacancies formation. Finally, the CO(2) capture evaluation shows that the aluminum presence into the Li(4)SiO(4) structure highly improves the CO(2) chemisorption, and on the contrary, vanadium addition inhibits it. The differences observed between the CO(2) chemisorption processes are mainly correlated to the different lithium secondary phases produced in each case and their corresponding diffusion properties.     

Phase range of the type-I clathrate Sr8Al(x)Si(46-x) and crystal structure of Sr8Al10Si36

Samples of the type-I clathrate Sr(8)Al(x)Si(46-x) have been prepared by direct reaction of the elements. The type-I clathrate structure (cubic space group Pm3n) which has an Al-Si framework with Sr(2+) guest atoms forms with a narrow composition range of 9.54(6) ≤ x ≤ 10.30(8). Single crystals with composition A(8)Al(10)Si(36) (A = Sr, Ba) have been synthesized. Differential scanning calorimetry (DSC) measurements provide evidence for a peritectic reaction and melting point at ～1268 and ～1421 K for Sr(8)Al(10)Si(36) and Ba(8)Al(10)Si(36), respectively. Comparison of the structures reveals a strong correlation between the 24k-24k framework sites distances and the size of the guest cation. Electronic structure calculation and bonding analysis were carried out for the ordered models with the compositions A(8)Al(6)Si(40) (6c site occupied completely by Al) and A(8)Al(16)Si(30) (16i site occupied completely with Al). Analysis of the distribution of the electron localizability indicator (ELI) confirms that the Si-Si bonds are covalent, the Al-Si bonds are polar covalent, and the guest and the framework bonds are ionic in nature. The Sr(8)Al(6)Si(40) phase has a very small band gap that is closed upon additional Al, as observed in Sr(8)Al(16)Si(30). An explanation for the absence of a semiconducting "Sr(8)Al(16)Si(30)" phase is suggested in light of these findings.     

Homoleptic imidazolate frameworks [Sr(1-x)Eu(x)(Im)2]--hybrid materials with efficient and tuneable luminescence

Homoleptic frameworks of the formula [Sr(1-x)Eu(x)(Im)(2)] (1) (x = 0.01-1.0; Im(-) = imidazolate anion, C(3)H(3)N(2)(-)) are hybrid materials that exhibit an intensive green luminescence. Tuning of both emission wavelength and quantum yield is achieved by europium/strontium substitution so that a QE of 80% is reached at a Eu content of 5%. Even 100% pure europium imidazolate still shows 60% absolute quantum efficiency. Substitution of Sr/Eu shows that doping with metal cations can also be utilized for coordination compounds to optimize materials properties. The emission is finely tuneable in the region 495-508 nm via variation of the europium content. The series of frameworks [Sr(1-x)Eu(x)(Im)(2)] presents dense MOFs with the highest quantum yields reported for MOFs so far.     

Ba2(BO3)(1-x)(CO3)(x)Cl(1+x): a mixed borate and carbonate chloride crystallized from high-temperature solution

A mixed borate and carbonate chloride Ba(2)(BO(3))(1-x)(CO(3))(x)Cl(1+x) was obtained by spontaneous crystallization from a high-temperature melt in open air. It crystallizes in the trigonal crystal system with space group of P3m?1 and lattice constants of a = 5.4708(8) ? and c = 10.640(2) ?. The structure can be viewed as an intergrowth of trigonal Ba(2)Mg(BO(3))(2) (001) slab and (111) slab of the cubic fluorite BaCl(2). During Fourier analysis of the single-crystal X-ray diffraction data, additional electron density was found locating at 1b (0, 0, 1/2) site and attributed to chlorine surplus, which was confirmed by chemical titration. Charge balance of the compound was found, unexpectedly in an acidic borate containing high-temperature melt, by partial CO(3)(2-) group substituting the BO(3)(3-) group. The existence of CO(3)(2-) anion in the crystal was detected by thermogravimetry-mass spectrum analysis and Raman spectrum. The transmittance spectrum shows that the crystal is transparent from ultraviolet to infrared with short-wavelength absorption edge at about 220 nm.     

Ba2Gd2(Si4O13): a silicate with finite Si4O13 chains

The title compound, dibarium digadolinium(III) tetrasilicate, crystallized from a molybdate‐based flux. It represents a new structure type and contains finite zigzag‐shaped C₂‐symmetric Si₄O₁₃ chains and Gd₂O₁₂ dimers built of edge‐sharing GdO₇ polyhedra. The [9+1]‐coordinated Ba atoms are located in voids in the atomic arrangement. All atoms are in general positions except for one O atom, which lies on a twofold axis. The structure is compared with those of the few other known tetrasilicates.     

New perovskite materials of the La(2-x)Sr(x)CoTiO6 series

Substitution of La(3+) by Sr(2+) in the double perovskite La(2)CoTiO(6) yields materials of the La(2-x)Sr(x)CoTiO(6) series showing a significant amount of trivalent cobalt ions when prepared at ambient atmosphere. The as-prepared compounds can be reduced in severe conditions retaining the perovskite structure while inducing the formation of a large amount of oxygen vacancies. The limit of aliovalent substitution in this series was found to extend up to x = 1. For substitution of La(3+) up to 15% cobalt and titanium are ordered, though the order is progressively lost as x increases; for x≥ 0.30 no ordering is observed as evidenced by magnetic measurements. The ability of these materials to present either cobalt ions in a mixed oxidation state or large amounts of anion vacancies depending on the atmosphere makes them interesting to be further investigated regarding their electrical and electrochemical properties, and hence, their usefulness in some electrochemical devices.     

Ca(1)(-)(x)Na(2)(x)Al(2)B(2)O(7): a structure with tunable density of Na(+) vacancies

A series of samples with the composition Ca(1)(-)(x)Na(2)(x)Al(2)B(2)O(7) (0 < x < or = 1) was investigated and a hexagonal structure with unusually large range of homogeneity (at least from x = 0.01 to 0.95) was revealed. The hexagonal phase consists of [Al(2)B(2)O(7)](infinity)(2)(-) lamellae stacked along the c axis, as in CaAl(2)B(2)O(7) and Na(2)Al(2)B(2)O(7). Nevertheless, the configuration and stacking sequence of the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae are different in these three structures. In the hexagonal structure of Ca(1)(-)(x)()Na(2)(x)()Al(2)B(2)O(7), Ca and half Na cations (Na1) statistically occupy the same crystallographic site which is located between the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae, the other half Na cations (Na2) distribute in the planes bisecting the [Al(2)B(2)O(7)](infinity)(2)(-) lamellae. Depending on the composition, the site occupation factor of Na2 site can vary in the same range as x, leading to a tunable density of Na(+) vacancies in the structure. The AlO(4) tetrahedra and BO(3) triangles in the structure tilt in appropriate ways to improve the bond valence sum of Na2 cations which are not sufficiently bonded to the anions.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.     

17O NMR and computational study of a tetrasiliconiobate ion, [H(2+x)Si4Nb16O56](14-x)-

Rates of oxygen-isotope exchange were measured in the tetrasiliconiobate ion [H(2+x)Si(4)Nb(16)O(56)]((14-x)-) to better understand how large oxide ions interact with water. The molecule has 19 nonequivalent oxygen sites and is sufficiently complex to evaluate hypotheses derived from our previous work on smaller clusters. We want to examine the extent to which individual oxygen atoms react independently with particular attention given to the order of protonation of the various oxygen sites as the pH decreases from 13 to 6. As in our previous work, we find that the set of oxygen sites reacts at rates that vary over approximately 10(4) across the molecule at 6相似文献   

Small gas-phase dianions of Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-)

We have searched for new species of small oxygen-containing gas-phase dianions produced in a secondary ion mass spectrometer by Cs+ ion bombardment of solid samples with simultaneous exposure of their surfaces to O2 gas. The targets were a pure zinc metal foil, a copper-contaminated zinc-based coin, two silicon-germanium samples (Si(1-x)Ge(x)(with x= 6.5% or 27%)) and a piece of titanium metal. The novel dianions Zn3O(4)(2-), Zn4O(5)(2-), CuZn2O(4)(2-), Si2GeO(6)(2-), Ti2O(5)(2-) and Ti3O(7)(2-) have been observed at half-integer m/z values in the negative ion mass spectra. The heptamer dianions Zn3O(4)(2-) and Ti2O(5)(2-) have been unambiguously identified by their isotopic abundances. Their flight times through the mass spectrometer are approximately 20 micros and approximately 17 micros, respectively. The geometrical structures of the two heptamer dianions Ti2O(5)(2-), and Zn3O(4)(2-) are investigated using ab initio methods, and the identified isomers are compared to those of the novel Ge2O(5)(2-) and the known Si2O(5)(2-) and Be3O(4)(2-) dianions.     

Structurally complex cobalt intermetallics grown from liquid aluminum: Co19Al45Si(10-x) (x = 0.13) and Co5Al14Si2

The cobalt aluminum silicides Co19Al45Si(10-x) (x = 0.13) and Co5Al14Si2 were synthesized in liquid aluminum and characterized by single-crystal X-ray diffraction. Co19Al45Si(10-x) (x = 0.13) crystallizes in the monoclinic space group C2/c with lattice parameters a = 19.991(2) A, b = 19.143(2) A, c = 12.8137(15) A, beta = 123.583(2) degrees. Co5Al14Si2 adopts the orthorhombic space group Pnma with cell parameters a = 13.8948(19) A, b = 23.039(3) A, c = 7.3397(10) A. Both structures are exceptionally complex with the Co2Si2 rhombus being a common building motif. The coordination environments of cobalt atoms resemble those of the transition metals in typical quasi-crystal approximants. Co5Al14Si2 shows oxidation resistance in air up to 1000 degrees C by forming a dense-packed Al2O3 layer on the surface of the crystal.     

Ca掺杂的Ba2Al2Si10N14O4:Eu2+荧光粉发光性能

通过固相反应制备了系列Ca掺杂的Ba2Al2Si10M14O4:Eu2+色荧光粉,发现当半径较大的Ba被Ca取代后导致了晶格的收缩,通过X射线衍射(XRD)测量和Unitcell软件计算发现Ca的最大掺杂量在20％.Ca掺人Eu0.4Ba1.6Al2Si10N14O4荧光粉后,可有效地提高光转换性能,并使激发光谱发生一定程度的红移和宽化,从而被近紫外宽波段光有效激发,与近紫外LED的发射光谱匹配.同时Ca的掺杂也使发射光谱发生了可控的红移,可以由520 nm的绿光红移至548 nm的黄光区域.进一步发现Eu2+的淬灭浓度随着20％ Ca的掺入而降低,这是由于Ca掺入导致的晶格收缩使Eu2+离子间距离减小.最后在CIE色度图中对不同Ca,Eu浓度的荧光粉的色坐标位置进行比较,发现可通过Ca,Eu浓度的变化在很大范围内调制荧光粉的发光性能.     

Further evidence for the tetraoxoiodate(V) anion,IO(4)(3-): hydrothermal syntheses and structures of Ba[(MoO(2))(6)(IO(4))(2)O(4)] x H(2)O and Ba(3)[(MoO(2))(2)(IO(6))(2)] x 2H(2)O

The hydrothermal reaction of MoO(3) with BaH(3)IO(6) at 180 degrees C for 3 days results in the formation of Ba[(MoO(2))(6)(IO(4))(2)O(4)] x H(2)O (1). Under similar conditions, the reaction of Ba(OH)(2) x 8H(2)O with MoO(3) and Ba(IO(4))(2) x 6H(2)O yields Ba(3)[(MoO(2))(2)(IO(6))(2)] x 2H(2)O (2). The structure of 1, determined by single-crystal X-ray diffraction, consists of corner- and edge-sharing distorted MoO(6) octahedra that create two-dimensional slabs. Contained within this molybdenum oxide framework are approximately C(2v) tetraoxoiodate(V) anions, IO(4)(3-), that are involved in bonding with five Mo(VI) centers. The two equatorial oxygen atoms of the IO(4)(3-) anion chelate a single Mo(VI) center, whereas the axial atoms are mu(3)-oxo groups and complete the octahedra of four MoO(6) units. The coordination of the tetraoxoiodate(V) anion to these five highly electropositive centers is probably responsible for stabilizing the substantial anionic charge of this anion. The Ba(2+) cations separate the layers from one another and form long ionic contacts with neighboring oxygen atoms and a water molecule. Compound 2 also contains distorted MoO(6) octahedra. However, these solely edge-share with octahedral hexaoxoiodate(VII), IO(6)(5-), anions to form zigzagging one-dimensional, (1)(infinity)[(MoO(2))(IO(6))](3-), chains that are polar. These chains are separated from one another by Ba(2+) cations that are coordinated by additional water molecules. Bond valence sums for the iodine atoms in 1 and 2 are 5.01 and 7.03, respectively. Crystallographic data: 1, monoclinic, space group C2/c, a = 13.584(1) A, b = 7.3977(7) A, c = 20.736(2) A, beta = 108.244(2) degrees, Z = 4; 2, orthorhombic, space group Fdd2, a = 13.356(7) A, b = 45.54(2) A, c = 4.867(3) A, Z = 8.     

Alloyed (ZnS)(x)(Cu2SnS3)(1-x) and (CuInS2)(x)(Cu2SnS3)(1-x) nanocrystals with arbitrary composition and broad tunable band gaps

Cu(2)SnS(3) nanocrystals with metastable zincblende and wurtzite structures have been successfully synthesized for the first time. Alloyed (ZnS)(x)(Cu(2)SnS(3))(1-x) and (CuInS(2))(x)(Cu(2)SnS(3))(1-x) nanocrystals with arbitrary composition (0 ≤x≤ 1) and ultra-broad tunable band gaps (3.63 to 0.94 eV) were obtained.     

A full interionic potential for Na(1+x)Zr(2)Si(x)P(3-x)O(12) superionic conductors

Most inorganic solids are made up of octahedral and tetrahedral units interconnected to give an infinite framework. Use of computer simulation to study these materials has not been as prevalent as in the organic or biomolecules. Na(1+x)Zr(2)Si(x)P(3-x)O(12) is a typical inorganic solid with ZrO(6) octahedra and (Si/P)O(4) tetrahedra which are shown along with a few Na(+) sites marked M1, M2, and M3. We report here a full interionic potential which reproduces the structure and conductivity of these solids. This augurs well for the study of other inorganic solids.     

Hydrothermal growth and structural studies of Si(1-x)Ge(x)O2 single crystals

The substitution of germanium in the α-quartz structure is a method investigated to improve the piezoelectric properties and the thermal stability of α-quartz. Growth of α-quartz type Si(1-x)Ge(x)O(2) single crystals was performed using a temperature gradient hydrothermal method under different experimental conditions (pressure, temperature, nature of the solvent, and the nutrient). To avoid the difference of dissolution kinetics between pure SiO(2) and pure GeO(2), single phases Si(1-x)Ge(x)O(2) solid solutions were prepared and used as nutrients. The influence of the nature (cristobalite-type, glass) and the composition of this nutrient were also studied. Single crystals were grown in aqueous NaOH (0.2-1 M) solutions and in pure water. A wide range of pressures (95-280 MPa) and temperatures (315-505 °C) was investigated. Structures of single crystals with x = 0.07, 0.1, and 0.13 were refined, and it was shown that the structural distortion (i.e., θ and δ) increases with the atomic fraction of Ge in an almost linear way. Thus, the piezoelectric properties of Si(1-x)Ge(x)O(2) solid solution should increase with x, and this material could be a good candidate for technological applications requiring a high piezoelectric coupling factor or high thermal stability.     

Novel quaternary lanthanum bismuth sulfides Pb(2)La(x)Bi(8-x)(S(14)), Sr(2)La(x)Bi(8-x)S(14), and Cs(2)La(x)Bi(10-x)S(16) with complex structures

The compounds Pb(2)La(x)Bi(8-x)S(14) (I), Sr(2)La(x)Bi(8-x)S(14) (II), and Cs(2)La(x)Bi(10-x)S(16) (III) were synthesized from the corresponding elements or binary sulfides at temperatures above 850 degrees C. Compounds I and II are isostructural, forming a new structure type, while the structure of III is related to the structure of the mineral kobellite. All compounds crystallize in the orthorhombic space group Pnma (No. 62) with a = 21.2592(4) A, b = 4.0418(1) A, c = 28.1718(3) A, Z = 4 for I, a = 21.190(1) A, b = 4.0417(2) A, c = 28.285(2) A, Z = 4 for II and a = 34.893(4) A, b = 4.0697(4) A, c = 21.508(2) A, Z = 4 for III. All compounds exhibit mixed site occupancy between Bi and La. Furthermore, I and II exhibit disorder between the divalent atom (Sr or Pb) and/or La and/or Bi. The structures of I and II consist of thin walls made of two metal-atom-thick NaCl-type blocks running in two opposite directions in the ac plane, forming rhombus-shaped tunnels. These tunnels are filled with Bi(2)Te(3)-type fragments. In the points where the walls intersect they form Gd(2)S(3)-type fragments. The structure of III consists of a complex three-dimensional framework with Cs-filled tunnels. All compounds are semiconductors with band gaps around 1.0 eV, and they melt around 740-860 degrees C.     

Mixed-valence uranium germanate and silicate: Cs(x)(U(V)O)(U(IV/V)O)2(Ge2O7)2 (x = 3.18) and Cs4(U(V)O)(U(IV/V)O)2(Si2O7)2

A new mixed-valence uranium germanate and the silicate analogue have been synthesized under hydrothermal conditions at 600 °C and 165 MPa. Their crystal structures contain infinite -U(V)-O-U(IV/V)-O-U(IV/V)-O-U(V)- chains that are connected by Ge(2)O(7) or Si(2)O(7) groups to form a 3D framework with six-ring channels where the Cs(+) cations are located. Two of the Cs sites in the germanate are partially occupied. Bond-valence-sum calculation and an U 4f X-ray photoelectron spectroscopy study confirm the valence states of the uranium.     

Crystal structures, Raman spectroscopy, and magnetic properties of Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29

The framework-deficient clathrate phases Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29 were prepared using a molten Al flux. Single-crystal X-ray diffraction confirmed the two phases to be clathrate type I (space group Pmn). For Eu0.27Ba7.22Al13Si29, single-crystal X-ray diffraction revealed the Eu to partially occupy the 2a position. Microprobe analysis of single crystals provided the stoichiometry, and Raman spectroscopy was used to investigate the guest framework interactions. The Raman spectra are consistent with both Ba7.5Al13Si29 and Eu0.27Ba7.22Al13Si29 having minimal guest-host interactions. Magnetic susceptibility data for Eu0.27Ba7.22Al13Si29 imply weak magnetic ordering and indicate a 2+ oxidation state for the Eu ion.