Crystal structure of novel compounds in the systems Zr-Cu-Al, Mo-Pd-Al and partial phase equilibria in the Mo-Pd-Al system

The crystal structures of three Al-rich compounds have been solved from X-ray single crystal diffractometry: τ(1)-MoPd(2-x)Al(8+x) (x = 0.067); τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) and τ(9)-ZrCu(1-x)Al(4) (x = 0.144). τ(1)-MoPd(2-x)Al(8+x) adopts a unique structure type (space group Pbcm; lattice parameters a = 0.78153(2), b = 1.02643(3) and c = 0.86098(2) nm), which can be conceived as a superstructure of the Mo(Cu(x)Al(1-x))(6)Al(4) type. Whereas Mo-atoms occupy the 4d site, Pd(2) occupies the 4c site, Al and Pd(1) atoms randomly share the 4d position and the rest of the positions are fully occupied by Al. A B?rnighausen tree documents the crystallographic group-subgroup relation between the structure types of Mo(Cu(x)Al(1-x))(6)Al(4) and τ(1). τ(7)-Zr(Cu(1-x)Al(x))(12) (x = 0.514) has been confirmed to crystallize with the ThMn(12) type (space group I4/mmm; lattice parameters a = 0.85243(2) and c = 0.50862(3) nm). In total, 4 crystallographic sites were defined, out of which, Zr occupies site 2a, the 8f site is fully occupied by Cu, the 8i site is entirely occupied by Al, but the 8j site turned out to comprise a random mixture of Cu and Al atoms. The compound τ(9)-ZrCu(1-x)Al(4) (x = 0.144) crystallizes in a unique structure type (space group P4/nmm; lattice parameters a = 0.40275(3) and c = 1.17688(4) nm) which exhibits full atom order but a vacancy (14.4%) on the 2c site, shared with Cu atoms. τ(9)-ZrCu(1-x)Al(4) is a superstructure of Cu with an arrangement of three unit cells of Cu in the direction of the c-axis. A B?rnighausen tree documents this relationship. The ZrCu(1-x)Al(4) type (n = 3) is part of a series of structures which follow this building principle: Cu (n = 1), TiAl(3) (n = 2), τ(5)-TiNi(2-x)Al(5) (n = 4), HfGa(2) (n = 6) and Cu(3)Pd (n = 7). A partial isothermal section for the Al-rich part of the Mo-Pd-Al system at 860 °C has been established with two ternary compounds τ(1)-MoPd(2-x)Al(8+x) and τ(2) (unknown structure). The Vickers hardness (H(v)) for τ(1) was found to be 842 ± 40 MPa.     

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.     

(η(2)-(Si/Ge)(4))Zn(η(2)-(Si/Ge)(4))](6-)- novel Zintl clusters with mixed Si/Ge tetrahedra bridged by a Zn atom

The solubility of the ternary Zintl phase K(12)Si(17-x)Ge(x) (x = 5), containing mixed group 14 element clusters, was investigated. Novel dimeric tetrahedral Zintl clusters [(η(2)-E(4))Zn(η(2)-E(4))](6-) with mixed site occupation (E = Si/Ge) were obtained through reaction with (C(6)H(6))(2)Zn in ammonia solutions and investigated by means of X-ray single crystal diffraction.     

Phase relations and crystal structure of τ6-Ti2(Ti(0.16)Ni(0.43)Al(0.41))3

Ti(2)(Ti(0.16)Ni(0.43)Al(0.41))(3) is a novel compound (labeled as τ(6)) in the Ti-rich region of the Ti-Ni-Al system in a limited temperature range 870 < T < 980 °C. The structure of τ(6)-Ti(2)(Ti,Ni,Al)(3) was solved from a combined analysis of X-ray single crystal and neutron powder diffracton data (space group C2/m, a = 1.85383(7) nm, b = 0.49970(2) nm, c = 0.81511(3) nm, and β = 99.597(3)°). τ(6)-Ti(2)(Ti,Ni,Al)(3) as a variant of the V(2)(Co(0.57)Si(0.43))(3)-type is a combination of slabs of the MgZn(2)-Laves type and slabs of the Zr(4)Al(3)-type forming a tetrahedrally close-packed Frank-Kasper structure with pentagon-triangle main layers. Titanium atoms occupy the vanadium sites, but Ti/Ni/Al atoms randomly share the (Co/Si) sites of V(2)(Co(0.57)Si(0.43))(3). Although τ(6) shows a random replacement on 6 of the 11 atom sites, it has no significant homogeneity range (~1 at. %). The composition of τ(6) changes slightly with temperature. DSC/DTA runs (1 K/min) were not sufficient to define proper reaction temperatures due to slow reaction kinetics. Therefore, phase equilibria related to τ(6) were derived from X-ray powder diffraction in combination with EPMA on alloys, which were annealed at carefully set temperatures and quenched. τ(6) forms from a peritectoid reaction η-(Ti,Al)(2)Ni + τ(3) + α(2) ? τ(6) at 980 °C and decomposes in a eutectoid reaction τ(6) ? η + τ(4) + α(2) at 870 °C. Both reactions involve the η-(Ti,Al)(2)Ni phase, for which the atom distribution was derived from X-ray single crystal intensity data, revealing Ti/Al randomly sharing the 48f- and 16c-positions in space group Fd3?m (Ti(2)Ni-type, a = 1.12543(3) nm). There was no residual electron density at the octahedral centers of the crystal structure ruling out impurity stabilization. Phase equilibria involving the τ(6) phase have been established for various temperatures (T = 865, 900, 925, 950, 975 °C, and subsolidus). The reaction isotherms concerning the τ(6) phase have been established and are summarized in a Schultz-Scheil diagram.     

Syntheses, structure, and bonding of Rb14(Mg1-xInx)30. A nonstoichiometric phase with an unusual substitution in the anion framework

The title compound Rb(14)(Mg(1-x)In(x))(30) (x = 0.79-0.88) has been obtained from high-temperature reactions of the elements in welded Ta tubes. There is no analogous binary compound without Mg. The crystal structure established by single-crystal X-ray diffraction means (space group P2m (No. 189), Z = 1 and a = b = 10.1593(3) Angstroms, c = 17.783(1) Angstroms for x = 0.851) features two distinct types of anionic layers: isolated pentacapped trigonal prismatic In(11)(7-) clusters and condensed [(Mg(x)In(1-x))(5)In(14)](7-) layers. The latter consists of analogous M(11) (M = Mg/In) fragments that share prismatic edges and are interbridged by trigonal M(3) units. The structure shows substantial differences from related A(15)Tl(27) (A = Rb, Cs) in which the cation A that centers a six-membered ring of Tl(11) fragments is replaced by M(3.) Both linear muffin-tin orbital and extended Hückel calculations are used to analyze the observed phase width and site preferences. We further utilize the results to rationalize the distortion of the M(11) fragment in the condensed layer and also to correlate with electrical properties. An isomorphous phase region (Rb(y)K(1-)(y))(14)(Mg(1-x)In(x))(30) (y = 0.52, 0.66 for x = 0.79) is also formed.     

XANES and XPS investigations of the local structure and final-state effects in amorphous metal silicates: (ZrO2)(x)(TiO2)(y)(SiO2)(1-x-y)

Amorphous quaternary [(ZrO(2))(x)(TiO(2))(y)(SiO(2))(1-x-y)] and ternary [(ZrO(2))(x)(SiO(2))(1-x)] silicates were synthesized using a sol-gel method and examined via XPS and XANES. Metal silicates are important industrial materials, though structural characterization is complicated because of their amorphous nature. Hard (Ti K- and Zr K-edge) and soft (Ti L(2,3)-edge) X-ray XANES spectra suggest the Ti and Zr coordination numbers in the quaternary silicates remain constant as the metal identity or total metal content (x, y, or x + y in the chemical formula) is varied. XPS core-line spectra from the quaternary silicates show large decreases in Ti 2p(3/2), Zr 3d(5/2), Si 2p(3/2), and O 1s binding energies due to increasing final-state relaxation with greater next-nearest neighbour substitution of Si for less-electronegative Ti/Zr, which was confirmed by analysis of the O Auger parameter. These decreases in binding energy occur without any changes in the ground-state energies (e.g., oxidation state) of these atoms, as examined by Ti L(2,3)-edge, Si L(2,3)-edge, and O K-edge XANES. Because most spectroscopic investigations are concerned with ground-state properties, knowledge of the contributions from final-state effects is important to understand the spectra from materials of interest.     

The chemistry and preparation of tantalum complexes with 2,3-dihydroxy benzoic acid: experimental and theoretical investigation

The effect of 2,3-dihydroxybenzoic acid (2,3DHBA, pyrocatechuic acid) on the chloro-alkoxo-species [TaCl(5-x)(OMe)(x)], formed by dissolving TaCl(5) in MeOH, has been studied. The coordination of 2,3DHBA-H(2)(-) on Ta (V) replacing MeO-terminal groups was monitored via NMR spectroscopy. The yellow solid 1 was isolated from the mixture of TaCl(5), with neutral 2,3-DHBA, in MeOH. From this solid the elemental (C, H and Ta), the thermogravimetric analyses, the IR, NMR, ESR and electronic spectra support the formula Ta(2)(2,3DHBA)(2)(O)(2)Cl(4)(MeO)(4). The ESR spectrum of solid 1, at 4.2 K, shows a half-field signal apart from a multiline signal around g=2, supporting evidence for semiquinone and Ta (IV) presence. The occurrence of superoxide radical, in the low temperature of ESR spectrum recording, cannot be ruled out. By heating the solid 1 at 500°C, an oxide phase showing porous character (SEM) and retaining CO(2) (IR), is evident. Solid 1 heated at 900°C, leads to the formation of β-Ta(2)O(5) orthorhombic phase, as the XRD pattern indicates. The hydrolytic process of solid 1, in aqueous solutions, has been studied; the presence of paramagnetic species generated in situ upon addition of base and the consequent degradative process of 2,3-DHBA, under aerobic conditions is obvious. In order to gain information for the structure of solid 1, DFT calculations have been performed for some theoretical models, based on the empirical formula of solid 1. The calculated structural and spectroscopic parameters have been correlated to experimental results. The energy optimized structures may give an idea about the way of MeCl and MeOMe formation as well some possible intermediates of the hydrolytic mechanism.     

Unexpected formation of a trinuclear complex containing a Ta(IV)-Ta(IV) bond in the reactions of Bu(t)N=Ta(NMe2)3 with silanes

A new trinuclear species containing a Ta(IV)-Ta(IV) bond, Ta(3)(μ-H)(μ-NMe(2))(μ=NBu(t))(2)(=NBu(t))(NMe(2))(5), has been formed by reductive elimination of H(2). Ta(2)H(2)(μ-NMe(2))(2)(NMe(2))(2)(=NBu(t))(2) has also been isolated. O(2) oxidizes the Ta(IV)-Ta(IV) bond to yield Ta(3)(μ(3)-O)(H)(μ=NBu(t))(μ-NMe(2))(2)(NMe(2))(4)(=NBu(t))(2) under ligand exchange. Delocalization of d electrons is discussed.     

Electron-deficient Eu(6.5)Gd(0.5)Ge6 intermetallic: a layered intergrowth phase of the Gd5Si4- and FeB-type structures

A novel electron-poor Eu(6.5)Gd(0.5)Ge? compound adopts the Ca?Sn?-type structure (space group Pnma, Z = 4, a = 7.5943(5) ?, b = 22.905(1) ?, c = 8.3610(4) ?, and V = 1454.4(1) ?3). The compound can be seen as an intergrowth of the Gd?Si?-type (Pnma) R?Ge? (R = rare earth) and FeB-type (Pnma) RGe compounds. The phase analysis suggests that the Eu(7-x)Gd(x)Ge? series displays a narrow homogneity range of stabilizing the Ca?Sn? structure at x ≈ 0.5. The structural results illustrate the structural rigidity of the 2(∝)[R?X?] slabs (X = p-element) and a possibility for discovering new intermetallics by combining the 2(∝)[R?X?] slabs with other symmetry-approximate building blocks. Electronic structure analysis suggests that the stability and composition of Eu(6.5)Gd(0.5)Ge? represents a compromise between the valence electron concentration, bonding, and existence of the neighboring EuGe and (Eu,Gd)?Ge? phases.     

Inelastic neutron scattering on three mixed-valence dodecanuclear polyoxovanadate clusters

The magnetic exchange interactions in the mixed-valence dodecanuclear polyoxovanadate compounds Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].23H(2)O, Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(D(2)O)].16.5D(2)O, and (NHEt(3))(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].H(2)O were investigated by an inelastic neutron scattering (INS) study using cold neutrons. In addition, the synthesis procedures and the single-crystal X-ray structures of these compounds have been investigated together with the temperature dependence of their magnetic susceptibilities. The magnetic properties below 100 K can be described by simply taking into account an antiferromagnetically exchange coupled tetramer, consisting of four vanadium(IV) ions. Up to four magnetic transitions between the cluster S = 0 ground state and excited states could be observed by INS. The transition energies and the relative INS intensities could be modeled on the basis of the following exchange Hamiltonian: H(ex) = -2J(12)(xy)[S(1x)S(2x)+ S(3x)S(4x)+ S(1y)S(2y)+ S(3y)S(4y)] - 2J(12)(z)[(S(1z)S(2z)+ S(3z)S(4z)] - 2J(23)(xy)[(S(2x)S(3x)+ S(1x)S(4x)+ S(2y)S(3y)+ S(1y)S(4y)] - 2J(23)(z)[(S(2z)S(3z)+ S(1z)S(4z)]. The following sets of parameters were derived: for Na(4)[V(12)As(8)O(40)(H(2)O)].23H(2)O, J(12)(xy)() = J(12)(z)= -0.80 meV, J(23)(xy) = J(23)(z) = -0.72 meV; for Na(4)[V(12)As(8)O(40)(D(2)O)].16.5D(2)O, J(12)(xy) = J(12)(z) = J(23)(xy) = J(23)(z = -0.78 meV; for (NHEt(3))(4)[V(12)As(8)O(40)(H(2)O)].H(2)O, J(12)(xy) = -0.80 meV, J(12)(z) = -0.82 meV, J(23)(xy)() = -0.67 meV, J(23)(z) = -0.69 meV. This study of the same [V(12)As(8)]-type cluster in three different crystal environments allows us to draw some conclusions concerning the applicability on INS in the area of nondeuterated molecular spin clusters. In addition, the effects of using nondeuterated samples and different sample container shapes for INS were evaluated.     

Epitaxial thin films of ATiO(3-x)H(x) (A = Ba, Sr, Ca) with metallic conductivity

Epitaxial thin films of titanium perovskite oxyhydride ATiO(3-x)H(x) (A = Ba, Sr, Ca) were prepared by CaH(2) reduction of epitaxial ATiO(3) thin films deposited on a (LaAlO(3))(0.3)(SrAl(0.5)Ta(0.5)O(3))(0.7) substrate. Secondary ion mass spectroscopy detected a substantial amount and uniform distribution of hydride within the film. SrTiO(3)/LSAT thin film hydridized at 530 °C for 1 day had hydride concentration of 4.0 × 10(21) atoms/cm(3) (i.e., SrTiO(2.75)H(0.25)). The electric resistivity of all the ATiO(3-x)H(x) films exhibited metallic (positive) temperature dependence, as opposed to negative as in BaTiO(3-x)H(x) powder, revealing that ATiO(3-x)H(x) are intrinsically metallic, with high conductivity of 10(2)-10(4) S/cm. Treatment with D(2) gas results in hydride/deuteride exchange of the films; these films should be valuable in further studies on hydride diffusion kinetics. Combined with the materials' inherent high electronic conductivity, new mixed electron/hydride ion conductors may also be possible.     

Cd(4)Cu(7)As, The First Representative of a Fully Ordered, Orthorhombically Distorted MgCu(2) Laves Phase

The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) ?; b = 7.1251(3) ?; c = 5.0895(4) ?. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m? with lattice parameter a = 7.0779(8) ?. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 ?(3) compared to 13 ?(3) for Cu) and higher ionicity in bonding.     

Phase evolution, phase transition, raman spectra, infrared spectra, and microwave dielectric properties of low temperature firing (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O4 ceramics with scheelite related structure

In the present work, the (K(0.5x)Bi(1-0.5x))(Mo(x)V(1-x))O(4) ceramics (0≤x ≤ 1.00) were prepared via the solid state reaction method and sintered at temperatures below 830 °C. At room temperature, the BiVO(4) scheelite monoclinic solid solution was formed in ceramic samples with x < 0.10. When x lies between 0.1-0.19, a BiVO(4) scheelite tetragonal phase was formed. The phase transition from scheelite monoclinic to scheelite tetragonal phase is a continuous, second order ferroelastic transition. High temperature X-ray diffraction results showed that this phase transition can also be induced at high temperatures about 62 °C for x = 0.09 sample, and has a monoclinic phase at room temperature. Two scheelite tetragonal phases, one being a BiVO(4) type and the other phase is a (K,Bi)(1/2)MoO(4) type, coexist in the compositional range 0.19 < x < 0.82. A pure (K,Bi)(1/2)MoO(4) tetragonal type solid solution can be obtained in the range 0.82 ≤ x ≤ 0.85. Between 0.88 ≤ x ≤ 1.0, a (K,Bi)(1/2)MoO(4) monoclinic solid solution region was observed. Excellent microwave dielectric performance with a relative dielectric permittivity around 78 and Qf value above 7800 GHz were achieved in ceramic samples near the ferroelastic phase boundary (at x = 0.09 and 0.10).     

Phase equilibria at 1375 K in three-component system of nickel-chromium-tantalum

The isothermal section of the phase equilibria diagram of the Ni-Cr-Ta system has been constructed at 1375 K by means of the method of equilibrium alloys and existence of six three-phase equilibria has been established, including γ-Ni + β-Cr + α; β-Cr + α + γ; α + γ + Ni₂Ta; γ + Ni₂Ta + μ; μ + γ + NiTa₂ and γ + NiTa₂ + β-Ta. It is shown that both cubic and hexagonal modifications are indicated in Laves binary phase.     

Solid state NMR characterization of individual compounds and solid solutions formed in Sc(2)O(3)--V(2)O(5)--Nb(2)O(5)--Ta(2)O(5) system

In this study, (51)V, (45)Sc and (93)Nb MAS NMR combined with satellite transition spectroscopy analysis were used to characterize the complex solid mixtures: VNb(9(1-x))Ta(9x)O(25), ScNb((1-x))Ta(x)O(4) and ScNb(2(1-x))Ta(2x)VO(9) (x = 0, 0.3, 0.5, 0.7, 1.0). This led us to describe the structures of Sc and V sites. The conclusions were based on accurate values for (51)V quadrupole coupling and chemical shift tensors obtained with (51)V MAS NMR/SATRAS for VNb(9)O(25), VTa(9)O(25) and ScVO(4). The (45)Sc NMR parameters have been obtained for Sc(2)O(3), ScVO(4), ScNbO(4) and ScTaO(4). On the basis of (45)Sc NMR and data available from literature, the ranges of the (45)Sc chemical shift have been established for ScO(6) and ScO(8). The gradual change of the (45)Sc and (51)V NMR parameters with x confirms the formation of solid solutions in the process of synthesis of VNb(9(1-x))Ta(9x)O(25) and ScNb((1-x))Ta(x)O(4), in contrast to ScNb(2(1-x))Ta(2x)VO(9). The cation sublattice of ScNb((1-x))Ta(x)O(4) is found to be in octahedral coordination. The V sites in VNb(9(1-x))Ta(9x)O(25) are present in the form of slightly distorted tetrahedra. The (93)Nb NMR parameters have been obtained for VNb(9)O(25).     

Synthesis, crystal structure, and physical properties of the type-I clathrate Ba(8-δ)Ni(x)□(y)Si(46-x-y)

Type-I clathrate phase Ba(8)Ni(x)□(y)Si(46-x-y) (□ = vacancy) was obtained from the elements at 1000 °C with the homogeneity range 2.4 ≤ x ≤ 3.8 and 0 ≤ y ≤ 0.9. In addition, samples with low Ni content (x = 1.4 and 1.6; y = 0) and small Ba deficiency were prepared from the melt by steel-quenching. Compositions were established by microprobe analysis and crystal structure determination. Ba(8-δ)Ni(x)□(y)Si(46-x-y) crystallizes in the space group Pm ?3n (No. 223) with lattice parameter ranging from a = 10.3088(1) ? for Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) to a = 10.2896(1) ? for Ba(8.00(3))Ni(3.82(4))Si(41.33(6)). Single-crystal X-ray diffraction data together with microprobe analysis indicate an increasing number of framework vacancies toward compositions with higher Ni content. For all compositions investigated, Ni K-edge X-ray absorption spectroscopy measurements showed an electronic state close to that of elemental Ni. All samples exhibit metallic-like behavior with moderate thermopower and low thermal conductivity in the temperature range 300-773 K. Samples with compositions Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) and Ba(7.9(1))Ni(1.6(1))Si(44.4(1)) are superconducting with T(c) values of 6.0 and 5.5 K, respectively.     

Thermochemistry of Sr2Ce(1-x)Pr(x)O4 (x = 0, 0.2, 0.5, 0.8, and 1): variable-temperature and -atmosphere in-situ and ex-situ powder X-ray diffraction studies and their physical properties

A novel family of metal oxides with a chemical formula of Sr(2)Ce(1-x)Pr(x)O(4) (x = 0, 0.2, 0.5, 0.8, and 1) was developed as mixed oxide ion and electronic conductors for solid oxide fuel cells (SOFCs). All of the investigated samples were synthesized by the ceramic method at 1000 °C in air and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). Ex-situ PXRD reveals that the Sr(2)PbO(4)-type Sr(2)CeO(4) decomposes readily into a mixture of perovskite-type SrCeO(3) and rock-salt-type SrO at 1400 °C in air. Surprisingly, the decomposed products are converted back to the original Sr(2)PbO(4)-type Sr(2)CeO(4) phase at 800 °C in air, as confirmed by in-situ PXRD. Thermal decomposition is highly suppressed in Sr(2)Ce(1-x)Pr(x)O(4) compounds for Pr > 0, suggesting that Pr improves the thermal stability of the compounds. Rietveld analysis of PXRD and SAED supported that both Pr and Ce ions are located on the 2a site in Pbam (space group no. 55). The electrical transport mechanism could be correlated to the reduction of Pr and/or Ce ions and subsequent loss of oxide ions at elevated temperatures, as shown by TGA and in-situ PXRD. Conductivity increases with Pr content in Sr(2)Ce(1-x)Pr(x)O(4). The highest total conductivity of 1.24 × 10(-1) S cm(-1) was observed for Sr(2)Ce(0.2)Pr(0.8)O(4) at 663 °C in air.     

Cd(1-x)Zn(x)O [0.05 ≤x≤ 0.26] synthesized by vapor-diffusion induced hydrolysis and co-nucleation from aqueous metal salt solutions

Nanoparticulate Cd(1-x)Zn(x)O (x = 0, 0.05-0.26, 1) is synthesized in a simple two-step synthesis approach. Vapor-diffusion induced catalytic hydrolysis of two molecular precursors at low temperature induces co-nucleation and polycondensation to produce bimetallic layered hydroxide salts (M = Cd, Zn) as precursor materials which are subsequently converted to Cd(1-x)Zn(x)O at 400 °C. Unlike ternary materials prepared by standard co-precipitation procedures, all products presented here containing < 30 mol% Zn(2+) ions are homogeneous in elemental composition on the micrometre scale. This measured compositional homogeneity within the samples, as determined by energy dispersive spectroscopy and inductively coupled plasma spectroscopy, is a testimony to the kinetic control achieved by employing slow hydrolysis conditions. In agreement with this observation, the optical properties of the materials obey Vegard's Law for a homogeneous solid solution of Cd(1-x)Zn(x)O, where x corresponds to the values determined by inductively coupled plasma analysis, even though powder X-ray diffraction shows phase separation into a cubic mixed metal oxide phase and a hexagonal ZnO phase at all doping levels.     

Synthesis of a family of solids through the building-block approach: a case study with Ag(+) substitution in the ternary Na-Ge-Se system

A new family of Ag-substituted pseudoquaternary alkali-seleno-germanates has been synthesized by two solid-state routes: the conventional flux method and metathesis. This family includes a series of semiconductors with varying amounts of Ag+ substituted for Na+ in Na8Ge4Se10 to form AgxNa(8-x)Ge4Se10, [x = 0.31 (I), 0.67 (II), 0.77 (III), 0.87 (IV), 1.05 (V), 1.09 (VI)] and another phase with a different composition AgxNa(6-x)Ge2Se7 (x = 1.76), VII, related to Na6Ge2Se7. In I-VI, Ge4Se10(8-) constitutes a 6-membered chairlike unit with a Ge-Ge bond, while in VII, a corner-shared dimer of GeSe4 tetrahedra (Ge2Se76-) acts as the building unit. The single-crystal structure analysis indicates that there is a phase transition from P to C2/c, in changing from pure Na8Ge4Se10 to AgxNa(8-x)Ge4 Se10 (I-VI), while there is no phase transition between pure Na6Ge2Se7 and AgxNa(6-x)Ge2Se7 (x = 1.76). The structures of I-VI may be described in terms of layers of cubic close-packed Se2- anions. In between the Se layers, octahedral holes fully occupied by Na+ and mixed Ag+/Na+ cations alternate with layers formed of octahedral holes fully occupied by Na+ and Ge26+ cations. Two adjacent Ge26+ cations form a chairlike Ge4Se10(8-) anion in which Ge-Ge bonds are oriented almost parallel to the Se layers. In contrast, VII does not have close-packed anions. Corner-shared GeSe4 tetrahedra (Ge2Se7(6-) dimer) and AgSe4 tetrahedra form layers that are cross-linked by Na/AgSe4 tetrahedra to form a 3-dimensional (3-D) structure. An optical property investigation indicates a red shift in the band gap of AgxNa(8-x)Ge4Se10 (x = 0.67)(II) as compared to that of pure Na8Ge4Se10. Raman data also indicate a red shift of the Ge-Se stretching mode in the Ag+-substituted phase II (x = 0.67) compared to that of Na8Ge4Se10.     

On the nature of ge-pb bonding in the solid state. Synthesis, structural characterization, and electronic structures of two unprecedented germanide-plumbides

Reported are the syntheses and the crystallographic characterization of two structurally related solid-state compounds: (Eu(1-x)Ca(x))(2)Ge(2)Pb (space group Pbam) and (Sr(x)Eu(1-x))(2)Ge(2)Pb (space group Cmmm). Both structures boast anionic sublattices with fully ordered Ge and Pb at the atomic level, which is unusual for elements of the same group. Despite the nearly identical formulas and the similar chemical makeup, the nature of the chemical bonding in the two compounds is subtly different; in the (Eu(1-x)Ca(x))(2)Ge(2)Pb structure, Ge and Pb are positioned at a relatively shorter distance from one another (<3.0 ?). The close proximity of the atoms leads to interactions, which are seen for the first time in an extended structure and can be suggested to have a covalent character. This conjecture is supported by extensive electronic band-structure calculations using first principles. Magnetic susceptibility measurements reveal Eu(2+) ground state ([Xe]4f(7) configuration) and the presence of an antiferromagnetic ordering at cryogenic temperatures.