Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

The crystal structures of three new intermetallic ternary compounds in the LnNiSb₃ (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb₃, NdNiSb₃ and SmNiSb₃ all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb₆ octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb₃), 4.6 K (NdNiSb₃), and 2.9 K (SmNiSb₃). Effective moments of 3.62 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

Structural and conductivity studies of CsKSO4Te(OH)6 and Rb1.25K0.75SO4Te(OH)6 materials

The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO₄Te(OH)₆ was found to crystallize in the monoclinic system with Pn space group and lattice parameters: ; ; ; β=106.53(2)°; ; Z=4 and . The structural refinement has led to a reliability factor of R₁=0.0284 (wR₂=0.064) for 7577 independent reflections. Rb_1.25K_0.75SO₄Te(OH)₆ material possesses a monoclinic structure with space group P2₁/a and cell parameters: ; ; ; β=106.860(10)°; ; Z=4 and . The residuals are R₁=0.0297 and wR₂=0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO₆⁶⁻ and SO₄²⁻) in the same crystal.Complex impedance measurements (Z^*=Z^′—iZ^″) have been undertaken in the frequency and temperature ranges 20-10⁶ Hz and 400-600 K, respectively. The dielectric relaxation is studied in the complex modulus formalism M^*.     

The disordered structures and low temperature dielectric relaxation properties of two misplaced-displacive cubic pyrochlores found in the Bi2O3-MO-Nb2O5 (M=Mg, Ni) systems

The disordered structures and low temperature dielectric relaxation properties of Bi_1.667Mg_0.70Nb_1.52O₇ (BMN) and Bi_1.67Ni_0.75Nb_1.50O₇ (BNN) misplaced-displacive cubic pyrochlores found in the Bi₂O₃-M^IIO-Nb₂O₅ (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B₂O₆ octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O′A₂ tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (, , ) to 96 h (, , ) while the O′ oxygen was shifted from position 8b (, , ) to Wyckoff position 32e (, , ). The refined displacement magnitudes off the 16d and 8b sites for the A and O′ sites were 0.408 Å/0.423 Å and 0.350 Å/0.369 Å for BMN/BNN, respectively.     

Synthesis and characterization of the rare-earth dicyanamides Ln[N(CN)2]3 with Ln=La, Ce, Pr, Nd, Sm, and Eu

The rare-earth dicyanamides Ln[N(CN)₂]₃ (Ln=La, Ce, Pr, Nd, Sm, Eu) were obtained via ion exchange in aqueous medium and subsequent drying: The crystal structures were solved and refined based on X-ray powder diffraction data and they were found to be isotypic: Ln[N(CN)₂]₃; Cmcm (no. 63), Z=4, Ln=La: , , ; Ce: , , ; Pr: , , ; Nd: , , ; Sm: , , ; Eu: , , ). The compounds represent the first dicyanamides with trivalent cations. The Ln³⁺ ions are coordinated by three bridging N atoms and six terminal N atoms of the dicyanamide ions forming a three capped trigonal prism. The structure type is related to that of PuBr₃. The novel compounds Ln[N(CN)₂]₃ have been characterized by IR and Raman spectroscopy (Ln=La) and the thermal behavior has been monitored by differential scanning calorimetry (Ln=Ce, Nd, Eu).     

Ag1/8Pr5/8MoO4: An incommensurately modulated scheelite-type structure

The crystal structure of a complex molybdenum oxide Ag_1/8Pr_5/8MoO₄ is reported. The Ag_1/8Pr_5/8MoO₄ sub-structure can be described on the base of the scheelite (CaWO₄) structure. Transmission electron microscopy reveals that the real structure is better described in a (3+1)D formalism. According to electron diffraction study the new scheelite-type complex oxide Ag_1/8Pr_5/8MoO₄ crystallizes in the B2/b(αβ0)00 (3+1)D superspace group with unit cell parameters , , and γ≈135° (Z=4) and modulation vector q=0.56a^*+0.59b^*. The structure of Ag_1/8Pr_5/8MoO₄ is refined from X-ray powder data in the scheelite setting I2/b(αβ0) with , , q=1.14690(14)a^*+0.58921(12)b^* with fixed γ=90° angle (R_p=0.033, R=0.033, R_m=0.029, R₁=0.047, S=1.36). Displacement modulations apply for all atoms. The occupancy modulation shows that one-fourth of the Ag/Pr atoms are absent. The structure can be considered as a crystallographic shear structure with incommensurate ordering of vacancies and displacement modulations for all atoms. The arrangement of Ag/Pr atoms and vacancies is at the origin of the incommensurate modulation in the cation-deficient Ag_1/8Pr_5/8MoO₄ phase.     

Structural characterization and ferroelectric ordering in (C3N2H5)5Sb2Br11

A ferroelectric crystal (C₃N₂H₅)₅Sb₂Br₁₁ has been synthesized. The single crystal X-ray diffraction studies (at 300, 155, 138 and 121 K) show that it is built up of discrete corner-sharing bioctahedra and highly disordered imidazolium cations. The room temperature crystal structure has been determined as monoclinic, space group, P2₁/n with: , and and β=96.19^°. The crystal undergoes three solid-solid phase transitions: ) discontinuous, continuous and discontinuous. The dielectric and pyroelectric measurements allow us to characterize the low temperature phases III and IV as ferroelectric with the Curie point at 145 K and the saturated spontaneous polarization value of the order of along the a-axis (135 K). The ferroelectric phase transition mechanism at 145 K is due to the dynamics of imidazolium cations.     

Growth of high quality and large-sized Rb0.3MoO3 single crystals by molten salt electrolysis method

High quality and large-sized Rb_0.3MoO₃ single crystals were synthesized by molten salt electrolysis method. X-ray diffraction (XRD) patterns and rocking curves, as well as the white beam Laue diffraction of X-ray images show the crystals grown by this method have high quality. The lattice constants evaluated from XRD patterns are a₀=1.87 nm, b₀=0.75 nm, c₀=1.00 nm, β=118.83^°. The in situ selected area electron diffraction (SAED) patterns along the , and zone axes at room temperature indicate that the Rb_0.3MoO₃ crystal possess perfect C-centered symmetry. Temperature dependence of the resistivity shows this compound undergoes a metal to semiconductor transition at 183 K.     

Synthesis and characteristics of a new three-dimensional molybdoantimonate Na4Sb12Mo5O35

A novel three-dimensional compound of Na₄Sb₁₂Mo₅O₃₅ has been synthesized by hydrothermal methods and structurally characterized by X-ray crystallography. It crystallizes in the triclinic system space group with , , , α=94.59(3)°, β=112.68(3)°, γ=92.97(3)°, , Z=2, R₁=0.0275, wR₂=0.0984 for 7364 unique reflections with I>2σ(I). The molecular structure is built up of Mo₆O₂₁, MoO₄ units, and cage-like units that contain 12 Sb atoms. IR, UV-Vis DRIS (Ultraviolet-Visible Diffuse Reflection Integral Spectrum), fluorescent spectra, and the thermogravimetric analysis of this compound were investigated.     

Crystal structures of Rb2U2O7 and Rb8U9O31, a new layered rubidium uranate

Two alkali metal uranates Rb₂U₂O₇ and Rb₈U₉O₃₁ have been synthesized by solid state reaction at high temperature and their crystal structures determined from single crystal X-ray diffraction data, collected with a three circles Brucker SMART diffractometer equipped by Mo(Kα) radiation and a charge-coupled device (CCD) detector. Their structures were solved using direct methods and Fourier difference techniques and refined by a least-square method on the basis of F² for all unique reflections, with R₁=0.043 for 53 parameters and 746 independent reflections with I?2σ(I) for Rb₂U₂O₇, monoclinic symmetry, space group P2₁/c, , , , β=108.81(1)°, , , Z=2 and R₁=0.036 for 141 parameters and 2065 independent reflections with I?2σ(I) for Rb₈U₉O₃₁, orthorhombic, space group Pbna, , , , , , Z=4.The Rb₂U₂O₇ structure presents a strong analogy with that of K₂U₂O₇ and can be described by layers of distorted UO₂(O₄) octahedra built from dimeric units of edge shared octahedra further linked together by opposite corners. In Rb₈U₉O₃₁ puckered layers are formed by the association of two different uranium polyhedra, pentagonal bipyramids and distorted octahedra. The structure of Rb₈U₉O₃₁ is built from a regular succession of infinite ribbons similar to those observed in diuranates M₂U₂O₇ (MK, Rb) and infinite three polyhedra wide ribbons , to create an original undulated sheets .For both compounds Rb⁺ ions occupy the interlayer space and exhibit comparable mobility with conductivity measurements indicating an Arrhenius-type behavior.     

Synthesis, structure, band gap, and electronic structure of CsAgSb4S7

The compound CsAgSb₄S₇ has been synthesized by the reaction of the elements in a Cs₂S₃ flux at 773 K. The compound crystallizes in a new structure type with eight formula units in space group C2/c of the monoclinic system in a cell at 153 K of dimensions , , , β=97.650(1)°, and . The structure contains two-dimensional layers separated by Cs atoms. Each layer is built from edge-sharing one-dimensional and chains. Each Ag atom is tetrahedrally coordinated to four S atoms. Each Sb³⁺ center is pyramidally coordinated to three S atoms to form an SbS₃ group. CsAgSb₄S₇ is insulating with an optical band gap of 2.04 eV. Extended Hückel calculations indicate that the band gap in CsAgSb₄S₇ is dominated by the Sb 5s and S 3p states above and below the Fermi level.     

Synthesis, crystal structure, and electronic structure of RbVSe2

RbVSe₂ has been synthesized at 773 K through the reaction of V and Se with a Rb₂Se₃ reactive flux. The compound crystallizes in the orthorhombic space group D_2h²⁴-Fddd with 16 formula units in a cell of dimensions , , and at . The structure possesses infinite one-dimensional chains of edge-sharing VSe₄ tetrahedra separated from the Rb⁺ ions. These chains distort slightly to chains. The V-V distance within these chains is 2.8362(4) Å. First-principles total energy calculations indicate that a non-magnetic configuration for the V³⁺ cations is the most stable.     

Crystal structure of cobalt molybdate hydrate CoMoO4·nH2O

We have determined the crystal structure of the title compound, which has a triclinic cell with cell parameters of , , , α=76.617°, β=84.188°, γ=74.510° and space group . The crystal structure suggests the chemical formula CoMoO₄·3/4H₂O. The structure consists of MoO₄ tetrahedra and CoO₆ octahedra, confirming the earlier X-ray absorption near-edge spectroscopic (XANES) investigation on the hydrate. The comparison of the crystal structures of the hydrate and the α-,β-, and hp-phases shows that the hydrate exhibits metal cation coordinations similar to those of the β-phase, but had arrangements of CoO₆ and MoO_n polyhedra similar to those of the hp-phase.     

Structures of the reduced niobium oxides Nb12O29 and Nb22O54

The crystal structure of Nb₂₂O₅₄ is reported for the first time, and the structure of orthorhombic Nb₁₂O₂₉ is reexamined, resolving previous ambiguities. Single crystal X-ray and electron diffraction were employed. These compounds were found to crystallize in the space groups P2/m (, , , β=102.029(3)^°) and Cmcm (, , ), respectively and share a common structural unit, a 4×3 block of corner sharing NbO₆ octahedra. Despite different constraints imposed by symmetry these blocks are very similar in both compounds. Within a block, it is found that the niobium atoms are not located in the centers of the oxygen octahedra, but rather are displaced inward toward the center of the block forming an apparent antiferroelectric state. Bond valence sums and bond lengths do not show the presence of charge ordering, suggesting that all 4d electrons are delocalized in these compounds at the temperature studied, T=200 K.     

In3Ir3B, In3Rh3B and In5Ir9B4, the first indium platinum metal borides

The first indium platinum metal borides have been synthesized and structurally characterized by single crystal X-ray diffraction data. In₃Ir₃B and In₃Rh₃B are isotypic. They crystallize with the hexagonal space group and Z=1. The lattice constants are , for In₃Ir₃B and , for In₃Rh₃B. The structure which is derived from the Fe₂P type is characterized by columns of boron centered triangular platinum metal prisms inserted in a three-dimensional indium matrix. The indium atoms are on split positions. In₅Ir₉B₄ (hexagonal, space group , , , Z=1) crystallizes with a structure derived from the CeCo₃B₂ type. The structure can be interpreted as a layer as well as a channel structure. In part the indium atoms are arranged at the vertices of a honeycomb net (Schlaefli symbol 6³) separating slabs consisting of double layers of triangular Ir₆B prisms, and in part they form a linear chain in a hexagonal channel formed by iridium prisms and indium atoms of the honeycomb lattice.     

Crystal structures and cation ordering of Sr2AlSbO6 and Sr2CoSbO6

The two double perovskite oxides Sr₂AlSbO₆ and Sr₂CoSbO₆ were prepared and their structures studied with the X-ray powder diffraction method. At room temperature the crystal structure of Sr₂AlSbO₆ is cubic , with . It was found that depending on the preparation conditions, the Al³⁺ and Sb⁵⁺ cations can be either entirely or partially ordered. In the case of the partially ordered Sr₂AlSbO₆ sample, the extension of cation ordering was estimated from the -dependent broadening of the diffraction peaks and the results were interpreted as evidence of the formation of anti-phase domains in the material. Low-temperature Raman spectroscopic measurements demonstrated that the cubic phase of Sr₂AlSbO₆ is stable down to 79 K.The room-temperature crystal structure of Sr₂CoSbO₆ is trigonal (space group with and . At 470 K, however, the material undergoes a continuous phase transition and its structure is converted to cubic (space group . The studied Sr₂CoSbO₆ sample was partially ordered, but unlike Sr₂AlSbO₆, no indication of the formation of anti-phase domains was observed.     

Synthesis and crystal structures of the layered uranyl tellurites A2[(UO2)3(TeO3)2O2] (A=K, Rb, Cs)

The reactions of UO₃ and TeO₃ with KCl, RbCl, or CsCl at 800 °C for 5 d yield single crystals of A₂[(UO₂)₃(TeO₃)₂O₂] (A=K (1), Rb (2), and Cs (3)). These compounds are isostructural with one another, and their structures consist of two-dimensional sheets arranged in a stair-like topology separated by alkali metal cations. These sheets are comprised of zigzagging uranium(VI) oxide chains bridged by corner-sharing trigonal pyramidal TeO₃²⁻ anions. The chains are composed of dimeric, edge-sharing, pentagonal bipyramidal UO₇ moieties joined by edge-sharing tetragonal bipyramidal UO₆ units. The lone-pair of electrons from the TeO₃ groups are oriented in opposite directions with respect to one another on each side of the sheets rendering each individual sheet non-polar. The alkali metal cations form contacts with nearby tellurite oxygen atoms as well as with oxygen atoms from the uranyl moieties. Crystallographic data (193 K, MoKα, ): 1, triclinic, space group , , , , α=101.852(1)°, β=102.974(1)°, γ=100.081(1)°, , Z=2, R(F)=2.70% for 98 parameters and 1697 reflections with I>2σ(I); 2, triclinic, space group , , , , α=105.590(2)°, β=101.760(2)°, γ=99.456(2)°, , Z=2, R(F)=2.36% for 98 parameters and 1817 reflections with I>2σ(I); 3, triclinic, space group , , , , α=109.301(1)°, β=100.573(1)°, γ=99.504(1)°, , Z=2, R(F)=2.61% for 98 parameters and 1965 reflections with I>2σ(I).