La0.5R0.5Ba2Cu3O7,Pr0.5R0.5Ba2Cu3O7以及RBa2Cu3o7（R=稀土）的键共价性计

使用复杂晶体化学键理论计算了Ｌａ０．５Ｒ０．５Ｂａ２Ｃｕ３Ｏ７（Ｒ＝Ｐｒ,Ｎｄ,Ｓｍ,Ｅｕ,Ｇｄ,Ｄｙ,Ｙ,Ｈｏ,Ｅｒ,Ｔｍ,Ｙｂ,Ｌｕ）（Ｌａ－Ｒ１２３）,Ｐｒ０．５Ｒ０．５Ｂａ２Ｃｕ３Ｏ７（Ｒ＝Ｌａ,Ｎｄ,Ｓｍ,Ｅｕ,Ｇｄ,Ｄｙ,Ｈｏ,Ｙ,Ｅｒ,Ｔｍ,Ｙｂ,Ｌｕ）（Ｐｒ－Ｒ１２３）以及ＲＢａ２Ｃｕ３Ｏ７（Ｒ＝Ｌａ,Ｐｒ,Ｎｄ,Ｓｍ,Ｅｕ,Ｇｄ,Ｄｙ,Ｈｏ,Ｙ,Ｅｒ,Ｔｍ）（Ｒ１２３）中Ｃｕ－Ｏ键的键共价性,结果表明Ｐｒ－Ｒ１２３,Ｌａ－Ｒ１２３,以及Ｒ１２３都应具有超导性,而实验结果是Ｌａ０．５Ｐｒ０．５Ｂａ２Ｃｕ０７,Ｒ０．５,Ｐｒ０．５Ｂａ２Ｃｕ３Ｏ７（Ｒ＝Ｌａ,Ｎｄ,Ｓｍ,Ｅｕ,Ｇｄ）无超导性,产生这种矛盾的原因尚不明确,需要做进一步的研究。     

First-principles density functional calculation of electrochemical stability of fast Li ion conducting garnet-type oxides

The research and development of rechargeable all-ceramic lithium batteries are vital to realize their considerable advantages over existing commercial lithium ion batteries in terms of size, energy density, and safety. A key part of such effort is the development of solid-state electrolyte materials with high Li(+) conductivity and good electrochemical stability; lithium-containing oxides with a garnet-type structure are known to satisfy the requirements to achieve both features. Using first-principles density functional theory (DFT), we investigated the electrochemical stability of garnet-type Li(x)La(3)M(2)O(12) (M = Ti, Zr, Nb, Ta, Sb, Bi; x = 5 or 7) materials against Li metal. We found that the electrochemical stability of such materials depends on their composition and structure. The electrochemical stability against Li metal was improved when a cation M was chosen with a low effective nuclear charge, that is, with a high screening constant for an unoccupied orbital. In fact, both our computational and experimental results show that Li(7)La(3)Zr(2)O(12) and Li(5)La(3)Ta(2)O(12) are inert to Li metal. In addition, the linkage of MO(6) octahedra in the crystal structure affects the electrochemical stability. For example, perovskite-type La(1/3)TaO(3) was found, both experimentally and computationally, to react with Li metal owing to the corner-sharing MO(6) octahedral network of La(1/3)TaO(3), even though it has the same constituent elements as garnet-type Li(5)La(3)Ta(2)O(12) (which is inert to Li metal and features isolated TaO(6) octahedra).     

Photoluminescence of perovskite nanosheets prepared by exfoliation of layered oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion)

Luminescent perovskite nanosheets were prepared by exfoliation of single- or double-layered perovskite oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). The thickness of the individual nanosheets corresponded to those of the perovskite block in the parent layered compounds. Intense red and green emissions were observed in aqueous solutions with Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets, respectively, under UV illumination with energies greater than the corresponding host oxide band gap. The coincidence of the excitation spectrum and the band gap absorbance indicates that the visible emission results from energy transfer within the nanosheet. The red emission intensity of the Gd1.4Eu0.6Ti3O10-nanosheets was much stronger than that of the La0.90Eu0.05Nb2O7-nanosheets reported previously. The strong emission intensity is a result of a two-step energy transfer cascade within the nanosheet from the Ti-O network to Gd(3+) and then to Eu(3+). The emission intensities of the Gd1.4Eu0.6Ti3O10- and La0.7Tb0.3Ta2O7-nanosheets can be modulated by applying a magnetic field (1.3-1.4 T), which brings about a change in orientation of the nanosheets in solution. The emission intensities increased when the excitation light and the magnetic field directions were perpendicular to each other, and they decreased when the excitation and magnetic field were collinear and mutually perpendicular to the direction of detection of the emitted light.     

Hydrothermal Synthesis and Characterization of Pyrochlore Titanate R2Ti2O7(R=Gd3+, Tb3+, Dy3+)

Pyrochlore titanate oxides, R2Ti2O7(R=Gd3+, Tb3+, Dy3+), were synthesized under mild hydrothermal conditions. The crystal growth of pyrochlore titanate oxides and taking place of chemical reaction in the hydrothermal processing were sensitive to the alkalinity, temperature, reaction time, the nature of the rare earth ion and the composition of initial reaction mixture. The as-prepared samples were characterized by powder X-ray diffraction, scanning electron microscopy, Raman spectrum and variable temperature dc magnetic susceptibility(SQUIDS). The magnetic studies gave 7.29×10–23 A•m2/Gd3+ and –8.28 K, 8.75×10–23 A•m2 /Tb3+ and –19.7 K, and 8.85×10–23 A•m2/Dy3+ and 0.84 K effective moments and Weiss constants for Gd2Ti2O7, Tb2Ti2O7 and Dy2Ti2O7, respectively.     

Crystal structure of novel R3Fe(Co,Ni)0.5SnS7 (R = Y,La, Ce,Pr, Nd,Sm, Gd,Tb, Dy and Ho) compounds

Structural Chemistry - The crystal structures of quaternary R3Fe0.5SnS7, R3Co0.5SnS7 and R3Ni0.5SnS7 (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Ho) compounds of La3Mn0.5SiS7 structure type (space...     

Near-edge X-ray absorption fine structure study of disordering in Gd2(Ti1-yZry)2O7 pyrochlores

Disorder in Gd2(Ti(1-y)Zry)2O7 pyrochlores, for y = 0.0-1.0, is investigated by Ti 2p and O 1s near-edge X-ray absorption fine structure spectroscopy. Ti(4+) ions are found to occupy octahedral sites in Gd2Ti2O7 with a tetragonal distortion induced by vacant oxygen sites. As Zr substitutes for Ti, the tetragonal distortion decreases, and Zr coordination increases from 6 to 8. The migration of oxygen ions from 48f or 8b sites to vacant 8a sites compensate for the increased Zr coordination, thereby reducing the number of vacant 8a sites, which further reduces the tetragonal distortion and introduces more disorder around Ti. This is evidence for simultaneous cation disorder with anion migration.     

New insights into the structural and dynamical features of lithium hexaoxometalates Li7MO6 (M = Nb, Ta, Sb, Bi)

We present a (re)investigation of the hexaoxometalates Li(8)MO(6) (M = Sn, Pb, Zr, Hf) and Li(7)MO(6) (M = Nb, Ta, Sb, Bi). Lithium motion and ionic conductivity in the hexaoxometalates were studied using impedance spectroscopy (for Li(7)MO(6), M = Sb, Bi, Ta) and (6)Li and (7)Li solid-state nuclear magnetic resonance (for Li(7)TaO(6)). The NMR data indicate a considerable exchange of Li among the tetrahedral and octahedral voids even at ambient temperature. In an investigation of the crystal structures using laboratory and synchrotron X-ray powder diffraction techniques, the structures of Li(7)TaO(6), Li(7)NbO(6), and Li(7)SbO(6) could be solved and refined. All three reveal a triclinic metric (Li(7)SbO(6), triclinic, P1, a = 5.38503(6) A, b = 5.89164(7) A, c = 5.43074(6) A, alpha = 117.2210(6) degrees, beta = 119.6311(6) degrees, gamma = 63.2520(7) degrees, V = 127.454(3) A(3), Z = 1; Li(7)NbO(6), triclinic, P1, a = 5.37932(9) A, b = 5.91942(11) A, c = 5.37922(9) A, alpha = 117.0033(9) degrees, beta = 119.6023(7) degrees, gamma = 63.2570(9) degrees, V = 126.938(4) A(3), Z = 1; Li(7)TaO(6), triclinic, P1, a = 5.38486(2) A, b = 5.92014(3) A, c = 5.38551(2) A, alpha = 117.0108(2) degrees, beta = 119.6132(2) degrees, gamma = 63.2492(2) degrees, V = 127.208(1) A(3), Z = 1.     

YTao4：Nb，Eu的发光性能研究

用高温固相反应法合成了铌酸根NbO^3-4和Eu^3 共掺杂的正钽酸盐化合物Y1－xEuxTa1-yNbyO4,研究该体系中紫外光和X射线激发下的发光性能,研究表明,在紫外光激发下,YTaO4:Nb,Eu是一种比较有效的红色发光材料,激发能可以通过NbO^3 4离子传递给Eu^3 ,随钽酸盐中NbO^3-4基团浓度的增中,化合物的结构从M'型YTaO4变成褐钇铌型YNbO4结构,它的发光性质也随之改变。     

New Materials Derived from Ybco: CrSr2RECu2O8 (RE = La, Pr, Nd, Eu, Gd, Tb, Dy, Y, Ho, Er, Lu)

Eleven new oxides, derived from yttrium barium copper oxide by replacing the square-planar copper [Cu-O4] of the basal plane of the triple perovskite-based structure with octahedral Cr(IV), have been prepared at high pressure and temperature. Their crystal structures have been determined, and their complex microstructure has been established by means of high-resolution electron microscopy and electron diffraction. The materials have a general formula of CrSr2RECu2O8 (RE = La, Pr, Nd, Eu, Gd, Tb, Dy, Y, Ho, Er, and Lu); they are tetragonal, show the symmetry of space group P4/mmm, and do not appear to be superconducting.     

Isolation of two-dimensional 2:1 cation-ordered perovskite units by anion vacancy ordering in Ba6Na2Nb2P2O17

A new six-layer perovskite-related structure Ba 6Na 2Nb 2M 2O 17 (M = P, V), which consists of cubic (c) BaO 3 layers and oxygen-deficient pseudocubic (c') BaO 2 layers stacked in the sequence c'ccccc, is presented. In Ba 6Na 2Nb 2M 2O 17, two-dimensional slabs of the well-known 2:1 octahedral cation-ordered perovskite motif are isolated between layers of tetrahedral units formed by anion vacancy ordering: two consecutive NbO 6 octahedral layers are sandwiched by two single NaO 6 octahedral layers, which, in turn, connect with two isolated MO 4 tetrahedral layers. Both oxides are derived from the 2:1 ordered perovskite structure (e.g., Ba 3ZnTa 2O 9) by ordered removal of O atoms in every sixth BaO 3 layer. Both materials exhibit a relative permittivity of approximately 20-23, Q x f 0 values of approximately 7800-10600 GHz, and negative temperature coefficients of the resonant frequency of approximately -23 to -7 ppm/ degrees C.     

Structures of novel R(2)Mo(5)O(18) and R(6)Mo(12)O(45) (R = Eu and Gd) prepared by thermal decomposition of polyoxomolybdate precursor [R2(H2O)(12)Mo(8)O(27)].nH2O

Single crystals of R(2)Mo(5)O(18) and R(6)Mo(12)O(45) (R = Eu and Gd), which are novel compounds in the R(2)O(3)-MoO(3) system, have been obtained by thermal decomposition of [R(2)(H(2)O)(12)Mo(8)O(27)].nH(2)O in air at 750 degrees C for 2 h. TG-DTA and X-ray diffractometry showed that R(2)Mo(5)O(18) crystallizes in a melt of the dehydrated precursor (R(2)Mo(8)O(27)), and R(2)Mo(5)O(18) is transformed to R(6)Mo(12)O(45) in the solid state, both occurring with the loss of MoO(3). R(2)Mo(5)O(18) species crystallize isostructurallyas orthorhombic, Pbcn, Z = 4, with lattice constants of a = 19.2612(7) and 19.246(1) A, b = 9.4618(3) and 9.4414(5) A, c = 9.3779(3) and 9.3446(4) A for R = Eu and Gd, respectively. R(6)Mo(12)O(45) crystallize isostructurally as triclinic P1, Z = 1, with lattice constants of a = 9.3867(4) and 9.3409(3) A, b = 10.9408(5) and 10.8826(5) A, c = 11.4817(5) and 11.4377(5) A, alpha = 104.194(2) degrees and 104.170(1) degrees, beta = 109.567(3) degrees and 109.288(4) degrees, gamma = 108.998(2) degrees and 109.266(2) degrees for R = Eu and Gd, respectively. Both structures consist of [RO(8)] square-antiprisms and [MoO(n)] polyhedra. In R(2)Mo(5)O(18), an [RO(8)] polyhedron is attached by only molybdate groups, being isolated from adjacent [RO(8)] groups. The 12 nearest R atoms surrounding an R atom with R...R distances of 6.0735(4)-7.0389(4) A form an approximate cuboctahedron. All the [RO(8)] square-antiprisms in R(6)Mo(12)O(45) are connected to each other by face-sharing to form dimeric [R(2)O(13)] and [R(2)O(12)] groups. The latter unusual [R(2)O(12)] group is achieved by sharing a square-face via four bridging O atoms with a very short R...R separation (3.4741(7) and 3.4502(6) A for R = Eu and Gd, respectively).     

Cation deficient layered Ruddlesden-Popper-related oxysulfides La2LnMS2O5 (Ln=La, Y; M=Nb, Ta)

The structures of the new oxysulfide Ruddlesden-Popper phases La2LnMS2O5 (Ln=La, Y; M=Nb, Ta) are reported together with an iodide-containing variant: La3-xNb1+xS2O5I2x (0相似文献   

Visible-light driven Gd2Ti2O7/GdCrO3 composite for hydrogen evolution

A series of Gd(2)Ti(2)O(7)/GdCrO(3) composites are prepared by solid state combustion method using Gd(NO(3))(3), TiO(2), Cr(2)O(3) as metal source and urea as a fuel. The composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectra (DRUV-vis), Brunauer-Emmett-Teller (BET) surface area measurements, photoluminescence spectra (PL), X-ray photoelectron spectroscopic (XPS) studies, photocurrent measurements etc. The photocatalytic activity of the composites is examined towards hydrogen production without using any co-catalyst under visible light illumination. The rate of formation of hydrogen is measured by the photocatalytic activity measurement device and gas chromatography (GC). The highest efficiency is observed over the composite GTC (Cr:Gd:Ti = 1:1:1). On the basis of photocurrent measurements and PL, a mechanism for the enhanced photocatalytic activity has been discussed.     

Hexachloroplatinates of the Lanthanides: Syntheses and Thermal Decomposition of [M(NO3)2(H2O)6]2[PtCl6]·2H2O (M = La,Pr) and [M(NO3)(H2O)7][PtCl6]·4H2O (M = Gd,Dy)

The reaction of the nitrates M(NO₃)₃·6H₂O (M = La, Pr) and (H₃O)₂PtCl₆ led to yellow single crystals of [M(NO₃)₂(H₂O)₆]₂[PtCl₆]·2H₂O (M = La, Pr) (monoclinic, P2₁/c, Z = 2, La/Pr: a = 697.4(3)/695.5(1), b = 1654.5(1)/1652.5(2), c = 1317.7(6)/1318.5(3) pm, β = 93.97°(7)/93.93°(2), R_all = 0.0169/0.0659) while the reaction of M(NO₃)₃·5H₂O (M = Gd, Dy) and (H₃O)₂PtCl₆ yielded yellow single crystals of [M(NO₃)(H₂O)₇][PtCl₆]·4H₂O (monoclinic, P2₁/n, Z = 4, Gd/Dy: a = 838.72(3)/838.40(2), b = 2131.98(6)/2139.50(7), c = 1142.63(3)/1143.10(3) pm, β = 95.670(4)/95.698(3), R_all = 0.0475/0.0337). The crystal structures consist of octahedral [PtCl₆]^2? anions and complex [M(NO₃)₂(H₂O)₆]₂⁺ and [M(NO₃)(H₂O)₇]²⁺ cations, respectively. The thermal decomposition of both types of compounds leads via various steps to elemental platinum and the oxide chlorides MOCl (M = La, Pr, Gd, Dy).     

2D-3D transformation of layered perovskites through metathesis: synthesis of new quadruple perovskites A2La2CuTi3O12 (A = Sr, Ca)

We describe the synthesis of two new quadruple perovskites, Sr(2)La(2)CuTi(3)O(12) (I) and Ca(2)La(2)CuTi(3)O(12) (II), by solid-state metathesis reaction between K(2)La(2)Ti(3)O(10) and A(2)CuO(2)Cl(2) (A = Sr, Ca). I is formed at 920 degrees C/12 h, and II, at 750 degrees C/24 h. Both the oxides crystallize in a tetragonal (P4/mmm) quadruple perovskite structure (a = 3.9098(2) and c = 15.794(1) A for I; a = 3.8729(5) and c = 15.689(2) A for II). We have determined the structures of I and II by Rietveld refinement of powder XRD data. The structure consists of perovskite-like octahedral CuO(4/2)O(2/2) sheets alternating with triple octahedral Ti(3)O(18/2) sheets along the c-direction. The refinement shows La/A disorder but no Cu/Ti disorder in the structure. The new cuprates show low magnetization (0.0065 micro(B) for I and 0.0033 micro(B) for II) suggesting that the Cu(II) spins are in an antiferromagnetically ordered state. Both I and II transform at high temperatures to 3D perovskites where La/Sr and Cu/Ti are disordered, suggesting that I and II are metastable phases having been formed in the low-temperature metathesis reaction. Interestingly, the reaction between K(2)La(2)Ti(3)O(10) and Ca(2)CuO(2)Cl(2) follows a different route at 650 degrees C, K(2)La(2)Ti(3)O(10) + Ca(2)CuO(2)Cl(2) --> CaLa(2)Ti(3)O(10) + CaCuO(2) + 2KCl, revealing multiple reaction pathways for metathesis reactions.     

Preparation, characterization and ESR studies of bulk and nano sized pyrochlore La2-xGdxZr2O7 (x=0.025, 0.05, 0.075 and 0.1)

Bulk and nano sized pyrochlore of composition La(2-x)Gd(x)Zr(2)O(7) (x=0.025, 0.05, 0.075 and 0.1) have been prepared by sol-gel method. They are characterized by powder X-ray diffraction and infrared spectroscopy. The sintering temperature influences the particle size of the sample. The room temperature powder ESR of La(1.95)Gd(0.05)Zr(2)O(7) gave characteristic "U" spectrum. The influence of particle size on the ESR of Gd(3+) is investigated. Possible reason for the disappearance of "U" spectrum with increase in the particle size is given.     

Mechanisms of the Solid-State Synthesis of Ln2SrFe2O7 (Ln = La,Nd, Gd,Dy) Layered Perovskite-Related Phases

Russian Journal of General Chemistry - The formation mechanisms for a series of n = 2 Ruddlesden-Popper phases Ln2SrFe2O7 (Ln = La, Nd, Gd, Dy) in the Ln2O3-SrO-Fe2O3 systems were determined. The...     

The System Bi2O3–R2O3 (R=Y,Gd)

A new face centered cubic phase of composition Bi₃RO₆ (R?Y, Gd) is reported, and details of the Bi₂O₃–R₂O₃ (R?Y, Gd) phase diagrams are discussed. Similar compositions with R?Tb, Dy, Hc, Er are examined.     

Phase relationships in the BaO-Ga2O3-Ta2O5 system and the structure of Ba6Ga21TaO40

Phase relationships in the BaO-Ga(2)O(3)-Ta(2)O(5) ternary system at 1200 °C were determined. The A(6)B(10)O(30) tetragonal tungsten bronze (TTB) related solution in the BaO-Ta(2)O(5) subsystem dissolved up to ~11 mol % Ga(2)O(3), forming a ternary trapezoid-shaped TTB-related solid solution region defined by the BaTa(2)O(6), Ba(1.1)Ta(5)O(13.6), Ba(1.58)Ga(0.92)Ta(4.08)O(13.16), and Ba(6)GaTa(9)O(30) compositions in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Two ternary phases Ba(6)Ga(21)TaO(40) and eight-layer twinned hexagonal perovskite solid solution Ba(8)Ga(4-x)Ta(4+0.6x)O(24) were confirmed in the BaO-Ga(2)O(3)-Ta(2)O(5) system. Ba(6)Ga(21)TaO(40) crystallized in a monoclinic cell of a = 15.9130(2) ?, b = 11.7309(1) ?, c = 5.13593(6) ?, β = 107.7893(9)°, and Z = 1 in space group C2/m. The structure of Ba(6)Ga(21)TaO(40) was solved by the charge flipping method, and it represents a three-dimensional (3D) mixed GaO(4) tetrahedral and GaO(6)/TaO(6) octahedral framework, forming mixed 1D 5/6-fold tunnels that accommodate the Ba cations along the c axis. The electrical property of Ba(6)Ga(21)TaO(40) was characterized by using ac impedance spectroscopy.     

Luminescent lanthanide selenites and tellurites decorated by MoO4 tetrahedra or MoO6 octahedra: Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12

Solid state reactions of lanthanide oxide, MoO3 and SeO2 (or TeO2) at high temperature in an evacuated quartz tube lead to four new Ln-Mo-Se(Te)-O quaternary phases with four different types of structures, namely, Nd2MoSe2O10, Gd2MoSe3O12, La2MoTe3O12, and Nd2MoTe3O12. The structure of Nd2MoSe2O10 features a 3D architecture built by the intergrowth of the Nd-Se-O layers with the Nd-Mo-O layers. The structure of Gd2MoSe3O12 contains a 3D network of gadolinium selenite with the MoO6 octahedra occupying the cavities of the structure. The structure of La2MoTe3O12 features a 3D network of La2(Te3O8)2+ with the tunnels along the a axis occupied by the MoO4 tetrahedra. Nd2MoTe3O12 features a 2D layer built by the lanthanide ions interconnected by tellurite groups and ditellurite groups, with the MoO4 tetrahedra as the interlayer pendant groups. Room temperature and low temperature luminescent studies indicate that Nd2MoSe2O10 and Nd2MoTe3O12 exhibit strong luminescence in the near-IR region.