Cu2Sc2Ge4O13, a novel germanate isotypic with the quasi-1D compound Cu2Fe2Ge4O13 between 100 and 298 K

The germanate compound Cu₂Sc₂Ge₄O₁₃ has been synthesized by solid-state ceramic sintering techniques between 1173 and 1423 K. The structure was solved from single-crystal data by Patterson methods. The title compound is monoclinic, a=12.336(2) Å, b=8.7034(9) Å, c=4.8883(8) Å, β=95.74(2), space group P2₁/m, Z=4. The compound is isotypic with Cu₂Fe₂Ge₄O₁₃, described very recently. The structure consists of crankshaft-like chains of edge-sharing ScO₆ octahedra running parallel to the crystallographic b-axis. These chains are linked laterally by [Cu₂O₆]⁸⁻ dimers forming a sheet of metal-oxygen-polyhedra within the a-b plane. These sheets are separated along the c-axis by [Ge₄O₁₃]¹⁰⁻ units. Cooling to 100 K does not alter the crystallographic symmetry of Cu₂Sc₂Ge₄O₁₃. While the b, c lattice parameter and the unit cell volume show a positive linear thermal expansion (α=6.4(2)×10⁻⁶, 5.0(2)×10⁻⁶ and 8.3(2)×10⁻⁶ K⁻¹ respectively), the a lattice parameter exhibits a negative thermal expansion (α=−3.0(2)×10⁻⁶ K⁻¹) for the complete T-range investigated. This negative thermal expansion of a is mainly due to the increase of the Cu-Cu interatomic distance, which is along the a-axis. Average bond lengths remain almost constant between 100 and 298 K, whereas individual ones partly show both significant shortages and lengthening.     

Structural and conductivity studies of Y10−xLaxW2O21

The aim of this work was to determine structural parameters of the Y_10−xLa_xW₂O₂₁ (x=0-10) solid solution series and investigate their electric properties. Crystallographic data shows a gradual increase in symmetry with increasing La content, as the structure evolves from orthorhombic, Y₁₀W₂O₂₁, towards the pseudo-cubic structure of Y₅La₅W₂O₂₁. The solubility limit of La₂O₃ was found to be 50% (x=5). Above this level two phases were observed, La₆W₂O₁₅ and (La,Y)_10+xW_2−xO_21−δ. The conductivity of Y rich samples was very low, with σ of the order 2×10⁻⁵-5×10⁻⁵ S cm⁻¹ at 1000 °C, whilst ionic conductivity was observed for most La rich doped samples. The highest conductivity was observed for La₁₀W₂O₂₁ and its doped analogues, at 1×10⁻³-5×10⁻³ S cm⁻¹ at 1000 °C. Unit cell parameters were determined as a function of temperature from 0 to 1000°C, and thermal expansion of these materials was determined from temperature studies carried out at the Australian Synchrotron facility in Melbourne, Victoria, Australia.     

Phase relations in the K2W2O7-K2WO4-KPO3-Bi2O3 system and structure of K6.5Bi2.5W4P6O34

The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory.     

New process of preparation, structure, and physicochemical investigations of the new titanyl phosphate Ti2O(H2O)(PO4)2

New titanyl phosphate Ti₂O(H₂O)(PO₄)₂ has been prepared and characterized by X-ray and neutron diffraction, nuclear magnetic resonance, infrared and Raman spectroscopies and thermogravimetric analysis. The crystal structure has been solved from neutron powder diffraction data at 300 K by Rietveld method in P2₁ space group. The refinement led to satisfactory profile factors (R_p=2.7%, R_wp=3.2%) and crystal structure model indicators (R_B=5.8%, R_F=3.2%). The cell is monoclinic with a=7.3735 Å, b=7.0405 Å, c=7.6609 Å and β=121.48°, Z=4. The structure can be described as a three-dimensional framework built up by chains of [TiO₅(OH₂)] octahedra with alternative short bonds [Ti₍₁₎-O₍₁₂₎; Ti₍₂₎-O₍₁₂₎, 1.88-1.84 Å] and long ones [Ti₍₁₎-O_W; Ti₍₂₎-O_W, 2.25-2.23 Å] along c-axis and connected via [PO₄] tetrahedra. Oxygen atom denoted O₍₁₂₎ is only linked to two titanium atoms and Oxygen atom denoted O_W is linked to two titanium atoms and two hydrogen atoms. O₍₁₂₎ and O_W are not linked to P atoms and justify the titanyl phosphate formulation Ti₂O(H₂O)(PO₄)₂. The infrared and Raman spectra presents peaks due to vibrations of Ti-O, P-O and O-H bonds. The ³¹P MAS NMR spectrum reveals two ³¹P resonance lines, in agreement with the structure which showed two crystallographic sites for phosphorus. The thermogravimetric analysis show that Ti₂O(H₂O)(PO₄)₂ is thermally stable until 400 °C. Above this temperature, it losses water and decomposes to Ti₅O₄(PO₄)₄ and TiP₂O₇.     

Neutron powder diffraction study of tetragonal Li7La3Hf2O12 with the garnet-related type structure

We have successfully synthesized a polycrystalline sample of tetragonal garnet-related Li-ion conductor Li₇La₃Hf₂O₁₂ by solid state reaction. The crystal structure is analyzed by the Rietveld method using neutron powder diffraction data. The structure analysis identifies that tetragonal Li₇La₃Hf₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.106(2) Å and c=12.630(2) Å with a cell ratio of c/a=0.9637. The crystal structure of tetragonal Li₇La₃Hf₂O₁₂ has the garnet-type framework structure composed of dodecahedral La(1)O₈, La(2)O₈ and octahedral HfO₆. Li atoms occupy three types of crystallographic site in the interstices of this framework structure, where Li(1) atom is located at the tetrahedral 8a site, and Li(2) and Li(3) atoms are located at the distorted octahedral 16f and 32g sites, respectively. These Li sites are filled with the Li atom. The present tetragonal Li₇La₃Hf₂O₁₂ sample exhibits bulk Li-ion conductivity of σ_b=9.85×10⁻⁷ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=4.45×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.53 eV in the temperature range of 300-580 K.     

Synthesis and crystal structure of new uranyl tungstates M2(UO2)(W2O8) (M=Na, K), M2(UO2)2(WO5)O (M=K, Rb), and Na10(UO2)8(W5O20)O8

The solid-state reactions of UO₃ and WO₃ with M₂CO₃ (M=Na, K, Rb) at 650°C for 5 days result, accordingly the starting stoichiometry, in the formation of M₂(UO₂)(W₂O₈) (M=Na (1), K (2)), M₂(UO₂)₂(WO₅)O (M=K (3), Rb (4)), and Na₁₀(UO₂)₈(W₅O₂₀)O₈ (5). The crystal structures of compounds 2, 3, 4, and 5 have been determined by single-crystal X-ray diffraction using Mo(Kα) radiation and a charge-coupled device detector. The crystal structures were solved by direct methods and Fourier difference techniques, and refined by a least-squares method on the basis of F² for all unique reflections. For (1), unit-cell parameters were determined from powder X-ray diffraction data. Crystallographic data: 1, monoclinic, a=12.736(4) Å, b=7.531(3) Å, c=8.493(3) Å, β=93.96(2)°, ρ_cal=6.62(2) g/cm³, ρ_mes=6.64(1) g/cm³, Z=4; 2, orthorhombic, space group Pmcn, a=7.5884(16) Å, b=8.6157(18) Å, c=13.946(3) Å, ρ_cal=6.15(2) g/cm³, ρ_mes=6.22(1) g/cm³, Z=8, R1=0.029 for 80 parameters with 1069 independent reflections; 3, monoclinic, space group P2₁/n, a=8.083(4) Å, b=28.724(5) Å, c=9.012(4) Å, β=102.14(1)°, ρ_cal=5.83(2) g/cm³, ρ_mes=5.90(2) g/cm³, Z=8, R1=0.037 for 171 parameters with 1471 reflections; 4, monoclinic, space group P2₁/n, a=8.234(1) Å, b=28.740(3) Å, c=9.378(1) Å, β=104.59(1)°, ρ_cal=6.13(2) g/cm³,  g/cm³, Z=8, R1=0.037 for 171 parameters with 1452 reflections; 5, monoclinic, space group C2/c, a=24.359(5) Å, b=23.506(5) Å, c=6.8068(14) Å, β=94.85(3)°, ρ_cal=6.42(2) g/cm³,  g/cm³, Z=8, R1=0.036 for 306 parameters with 5190 independent reflections. The crystal structure of 2 contains linear one-dimensional chains formed from edge-sharing UO₇ pentagonal bipyramids connected by two octahedra wide (W₂O₈) ribbons formed from two edge-sharing WO₆ octahedra connected together by corners. This arrangement leads to [UW₂O₁₀]²⁻ corrugated layers parallel to (001). Owing to the unit-cell parameters, compound 1 probably contains similar sheets parallel to (100). Compounds 3 and 4 are isostructural and the structure consists of bi-dimensional networks built from the edge- and corner-sharing UO₇ pentagonal bipyramids. This arrangement creates square sites occupied by W atoms, a fifth oxygen atom completes the coordination of W atoms to form WO₅ distorted square pyramids. The interspaces between the resulting [U₂WO₁₀]²⁻ layers parallel to plane are occupied by K or Rb atoms. The crystal structure of compound 5 is particularly original. It is based upon layers formed from UO₇ pentagonal bipyramids and two edge-shared octahedra units, W₂O₁₀, by the sharing of edges and corners. Two successive layers stacked along the [100] direction are pillared by WO₄ tetrahedra resulting in sheets of double layers. The sheets are separated by Na⁺ ions. The other Na⁺ ions occupy the rectangular tunnels created within the sheets. In fact complex anions W₅O₂₀¹⁰⁻ are built by the sharing of the four corners of a WO₄ tetrahedron with two W₂O₁₀ dimmers, so, the formula of compound 5 can be written Na₁₀(UO₂)₈(W₅O₂₀)O₈.     

Crystal structure and conductivity investigation of KDyP4O12: a new potassium dysprosium cyclotetraphosphate

A single-crystal X-ray diffraction analysis has been performed on KDyP₄O₁₂ synthesized by a flux method. The new compound crystallizes at room temperature in the monoclinic space group C2/c with unit cell parameters: a=7.812(2) Å, b=12.318(3) Å, c=10.441(2) Å, β=111.09(2)°, V=937.42(4) Å³ and D_cal=3.66 g cm⁻³ for Z=4. A full-matrix least square refinement gave R₁=0.022, wR₂=0.04 for 2421 independent reflections (I>2σ(I)) refined with 84 parameters.The structure is built up from P₄O₁₂⁴⁻ cyclotetraphosphate anions linked by DyO₈ polyhedra to form a three-dimensional framework, which delimits intersecting oxygen tunnels in which the K⁺ ions are located. The atomic arrangement can be described as a succession of layers extending along the [010] direction. The P₄O₁₂⁴⁻ ring anion is centrosymmetrical is connected by irregularly shaped KO₁₀ polyhedra to form a layer structure parallel to (001). Dysprosium and potassium are surrounded by eight and ten oxygen atoms respectively.Samples have been examined by impedance and infrared spectroscopy techniques. The reported IR absorption investigation, recorded at room temperature in the frequency range 200-4000 cm⁻¹, shows some bands characteristic of cyclotetraphosphates.The electrical conductivity of KDyP₄O₁₂ has subsequently been measured as a function of temperature, it represents a significant ionic conductivity and activation energy (σ=2.15×10⁻⁴ Ω⁻¹cm⁻¹ at 453 K and E_a=0.387 eV) corresponding to the mobility of the K⁺ cations located within tunnels.     

New one-dimensional uranyl and neptunyl iodates: crystal structures of K3[(UO2)2(IO3)6](IO3)·H2O and K[NpO2(IO3)3]·1.5H2O

The uranyl and neptunyl(VI) iodates, K₃[(UO₂)₂(IO₃)₆](IO₃)·H₂O (1) and K[NpO₂(IO₃)₃]·1.5H₂O (2), have been prepared and crystallized under mild hydrothermal conditions. The structures of 1 and 2 both contain one-dimensional _∞¹[AnO₂(IO₃)₃]¹⁻(An=U,Np) ribbons that consist of approximately linear actinyl(VI) cations bound by iodate anions to yield AnO₇ pentagonal bipyramids. The AnO₇ units are linked by bridging iodate anions to yield chains that are in turn coupled by additional iodate anions to yield ribbons. The edges of the ribbons are terminated by monodentate iodate anions. For 1 and 2, K⁺ cations and water molecules separate the ribbons from one another. In addition, isolated iodate anions are also found between _∞¹[UO₂(IO₃)₃]¹⁻ ribbons in 1. In order to aid in the assignment of oxidation states in neptunyl containing compounds, a bond-valence sum parameter of 2.018 Å for Np(VI) bound exclusively to oxygen has been developed with b=0.37 Å. Crystallographic data (193 K, MoKα, λ=0.71073): 1, triclinic, , a=7.0609(4) Å, b=14.5686(8)  Å, c=14.7047(8)  Å, α=119.547(1)°, β=95.256(1)°, γ=93.206(1)°, Z=2, R(F)=2.49% for 353 parameters with 6414 reflections with I>2σ(I); (203 K, MoKα, λ=0.71073): 2, monoclinic, P2₁/c, a=7.796(4)  Å, b=7.151(3)  Å, c=21.79(1)  Å, β=97.399(7)°, Z=4, R(F)=6.33% for 183 parameters with 2451 reflections with I>2σ(I).     

Synthesis, crystal structure and thermal behavior of a novel oxoborate SrBi2B4O10

A new compound, SrBi₂B₄O₁₀, has been grown by cooling a melt with the stoichiometric composition. It is triclinic, P−1, a=6.819(1), b=6.856(1), c=9.812(2) Å, α=96.09(1), β=109.11(1), γ=101.94(1)°, V=416.5(1) Å³, Z=2. The crystal structure of the compound has been solved by direct methods and refined to R₁=0.050 (wR₂=0.128). The structure contains Bi-O pseudolayers build up from Bi-O chains involving oxocentred OBi₃ triangles. Sr atoms and [B₄O₉]⁶⁻ isolated anions (4B:3Δ□:<2Δ□>Δ) are located between the Bi-O packages.The thermal treatment as well as DSC experiment showed that the compound melts above 800 °C presumably according to the peritectic reaction: SrBi₂B₄O₁₀ ↔ SrB₂O₄+SrB₄O₇+ Liquid. According to high-temperature X-ray powder diffraction study thermal expansion of SrBi₂B₄O₁₀ structure is anisotropic (α₁₁=13, α₂₂=9, α₃₃=2, α_V=24×10⁻⁶ °C⁻¹).     

The study of Bi3B5O12: synthesis, crystal structure and thermal expansion of oxoborate Bi3B5O12

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi₃B₅O₁₂. The Bi₃B₅O₁₂ single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi₃B₅O₁₂ was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) Å, V=937.2(5) Å³, Z=4, R=3.45%. Bi³⁺ atoms have irregular coordination polyhedra, Bi(1)O₆ (d(B-O)=2.09-2.75 Å) and Bi(2)O₇ (d(B-O)=2.108-2.804 Å). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O₃ (2.09-2.20 Å) and tetragonal Bi(2)O₄ (2.108-2.331 Å) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO₄ polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B₂^IVB₃^IIIO₁₁]⁷⁻ through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi-O chains. The Bi₃B₅O₁₂ thermal expansion is sharply anisotropic (α₁₁≈α₂₂=12, α₃₃=3×10⁻⁶ °C⁻¹) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains.     

Synthesis and crystal structure of the palladium oxides NaPd3O4, Na2PdO3 and K3Pd2O4

NaPd₃O₄, Na₂PdO₃ and K₃Pd₂O₄ have been prepared by solid-state reaction of Na₂O₂ or KO₂ and PdO in sealed silica tubes. Crystal structures of the synthesized phases were refined by the Rietveld method from X-ray powder diffraction data. NaPd₃O₄ (space group Pm3¯n, a=5.64979(6) Å, Z=2) is isostructural to NaPt₃O₄. It consists of NaO₈ cubes and PdO₄ squares, corner linked into a three-dimensional framework where the planes of neighboring PdO₄ squares are perpendicular to each other. Na₂PdO₃ (space group C2/c, a=5.3857(1) Å, b=9.3297(1) Å, c=10.8136(2) Å, β=99.437(2)°, Z=8) belongs to the Li₂RuO₃-structure type, being the layered variant of the NaCl structure, where the layers of octahedral interstices filled with Na⁺ and Pd⁴⁺ cations alternate with Na₃ layers along the c-axis. Na₂PdO₃ exhibits a stacking disorder, detected by electron diffraction and Rietveld refinement. K₃Pd₂O₄, prepared for the first time, crystallizes in the orthorhombic space group Cmcm (a=6.1751(6) Å, b=9.1772(12) Å, c=11.3402(12) Å, Z=4). Its structure is composed of planar PdO₄ units connected via common edges to form parallel staggered PdO₂ strips, where potassium atoms are located between them. Magnetic susceptibility measurements of K₃Pd₂O₄ reveal a Curie-Weiss behavior in the temperature range above 80 K.     

Synthesis, crystal structure and electrical characterization of two new potassium uranyl molybdates K2(UO2)2(MoO4)O2 and K8(UO2)8(MoO5)3O6

Two new potassium uranyl molybdates K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆ have been obtained by solid state chemistry . The crystal structures were determined by single crystal X-ray diffraction data, collected with MoKα 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=0.046 for 136 parameters and 1412 reflections with I?2σ(I) for K₂(UO₂)₂(MoO₄)O₂ and R₁=0.055 for 257 parameters and 2585 reflections with I?2σ(I) for K₈(UO₂)₈(MoO₅)₃O₆. The first compound crystallizes in the monoclinic symmetry, space group P2₁/c with a=8.250(1) Å, b=15.337(2) Å, c=8.351(1) Å, β=104.75(1)°, ρ_mes=5.22(2) g/cm³, ρ_cal=5.27(2) g/cm³ and Z=4. The second material adopts a tetragonal unit cell with a=b=23.488(3) Å, c=6.7857(11) Å, ρ_mes=5.44(3) g/cm³, ρ_cal=5.49(2) g/cm³, Z=4 and space group P4/n.In both structures, the uranium atoms adopt a UO₇ pentagonal bipyramid environment, molybdenum atoms are in a MoO₄ tetrahedral environment for K₂(UO₂)₂(MoO₄)O₂ and MoO₅ square pyramid coordination in K₈(UO₂)₈(MoO₅)₃O₆. These compounds are characterized by layered structures. The association of uranyl ions (UO₇) and molybdate oxoanions MoO₄ or MoO₅, give infinite layers [(UO₂)₂(MoO₄)O₂]²⁻ and [(UO₂)₈(MoO₅)₃O₆]⁸⁻ in K₂(UO₂)₂(MoO₄)O₂ and K₈(UO₂)₈(MoO₅)₃O₆, respectively. Conductivity properties of alkali metal within the interlayer spaces have been measured and show an Arrhenius type evolution.     

Synthesis crystal structure and ionic conductivity of Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10

Two new compounds Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀ have been synthesized in the ternary system: MO-Bi₂O₃-V₂O₅ system (M=M²⁺). The crystal structure of Sr_0.5Bi₃V₂O₁₀ has been determined from single crystal X-ray diffraction data, space group and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å³. Ca_0.5Bi₃V₂O₁₀ is isostructural with Sr_0.5Bi₃V₂O₁₀, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å³ and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi₂O₂) along c-axis formed by linkage of BiO₈ and BiO₆ polyhedra interconnected by MO₈ polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10⁻⁵ and 3.63×10⁻⁵ S cm⁻¹ for Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀, respectively at 725 °C.     

Synthesis, crystal structure and thermal behavior of Sr3B2SiO8 borosilicate

Single crystals of Sr₃B₂SiO₈ were obtained by solid-state reaction of stoichiometric mixture at 1200 °C. The crystal structure of the compound has been solved by direct methods and refined to R1=0.064 (wR=0.133). It is orthorhombic, Pnma, a=12.361(4), b=3.927(1), c=5.419(1) Å, V=263.05(11) Å³. The structure contains zigzag pseudo-chains running along the b axis and built up from corner sharing (Si,B)−O polyhedra. Boron and silicon are statistically distributed over one site with their coordination strongly disordered. Sr atoms are located between the chains providing three-dimensional linkage of the structure.The formation of Sr₃B₂SiO₈ has been studied using annealing series in air at 900-1200 °C. According powder XRD, the probe contains pure Sr₃B₂SiO₈ over 1100 °C. The compound is not stable below 900 °C. In the pseudobinary Sr₂B₂O₅-Sr₃B₂SiO₈ system a new series of solid solutions Sr_3−xB₂Si_1−xO_8−3x (x=0-0.9) have been crystallized from melt. The thermal behavior of Sr₃B₂SiO₈ was investigated using powder high-temperature X-ray diffraction (HTXRD) in the temperature range 20-900 °C. The anisotropic character of thermal expansion has been observed: α_a= −1.3, α_b=23.5, α_c=13.9, and α_V=36.1×10⁻⁶ °C⁻¹ (25 °C); α_a= −1.3, α_b=23.2, α_c=5.2, and α_V=27.1×10⁻⁶ °C⁻¹ (650 °C). Maximal thermal expansion of the structure along of the chain direction [0 1 0] is caused by the partial straightening of chain zigzag. Hinge mechanism of thermal expansion is discussed.     

LiB3O5 crystal structure at 20, 227 and 377 °C

Crystal structure of LiB₃O₅ (a framework of [B₃O₅]⁻ rings and Li atoms located in interspaces) was refined at high temperatures using single-crystal X-ray diffraction, MoKα-radiation, anharmonic approximation, orthorhombic; Pna2₁; Z=4; 20 °C (a=8.444, b=7.378, c=5.146 Å, 1411 F(hkl), R=0.022); 227 °C (a=8.616, b=7.433, c=5.063 Å, 1336 F(hkl), R=0.026), 377 °C (a=8.746, b=7.480, c=5.013 Å, 1193 F(hkl), R=0.035). A high mobility of Li atoms and their highly asymmetric vibrations are revealed. Ellipsoid of Li thermal vibrations is oviform. Li is shifted on heating to 0.26 Å mainly along a-axis causing high thermal expansion in this direction; Li temperature factors are multiplied by 4 on heating. Rigid boron-oxygen groups in LiB₃O₅ remain practically stable on heating similar to α-Na₂B₈O₁₃ and α-CsB₅O₈. At the same time these groups rotate relative to each other like hinges leading to extremely anisotropic thermal expansion (α_a=101, α_b=31, α_c=−71, α_v=60×10⁻⁶ °C⁻¹, 20-530 °C, HTXRPD data).     

New open-framework in the uranyl vanadates A3(UO2)7(VO4)5O (A=Li, Ag) with intergrowth structure between A(UO2)4(VO4)3 and A2(UO2)3(VO4)2O

New uranyl vanadates A₃(UO₂)₇(VO₄)₅O (M=Li (1), Na (2), Ag (3)) have been synthesized by solid-state reaction and their structures determined from single-crystal X-ray diffraction data for 1 and 3. The tetragonal structure results of an alternation of two types of sheets denoted S for _∞²[UO₂(VO₄)₂]⁴⁻ and D for _∞²[(UO₂)₂(VO₄)₃]⁵⁻ built from UO₆ square bipyramids and connected through VO₄ tetrahedra to _∞¹[U(3)O₅-U(4)O₅]⁸⁻ infinite chains of edge-shared U(3)O₇ and U(4)O₇ pentagonal bipyramids alternatively parallel to a- and b-axis to construct a three-dimensional uranyl vanadate arrangement. It is noticeable that similar _∞[UO₅]⁴⁻ chains are connected only by S-type sheets in A₂(UO₂)₃(VO₄)₂O and by D-type sheets in A(UO₂)₄(VO₄)₃, thus A₃(UO₂)₇(VO₄)₅O appears as an intergrowth structure between the two previously reported series. The mobility of the monovalent ion in the mutually perpendicular channels created in the three-dimensional arrangement is correlated to the occupation rate of the sites and by the geometry of the different sites occupied by either Na, Ag or Li. Crystallographic data: 293 K, Bruker X8-APEX2 X-ray diffractometer equipped with a 4 K CCD detector, MoKα, λ=0.71073 Å, tetragonal symmetry, space group P4¯m2, Z=1, full-matrix least-squares refinement on the basis of F²; 1,a=7.2794(9) Å, c=14.514(4) Å, R1=0.021 and wR2=0.048 for 62 parameters with 782 independent reflections with I?2σ(I); 3, a=7.2373(3) Å, c=14.7973(15) Å, R1=0.041 and wR2=0.085 for 60 parameters with 1066 independent reflections with I?2σ(I).     

Structure and properties of the CaFe2O4-type cobalt oxide CaCo2O4

The calcium cobalt oxide CaCo₂O₄ was synthesized for the first time and characterized from a powder X-ray diffraction study, measuring magnetic susceptibility, specific heat, electrical resistivity, and thermoelectric power. CaCo₂O₄ crystallizes in the CaFe₂O₄ (calcium ferrite)-type structure, consisting of an edge- and corner-shared CoO₆ octahedral network. The structure of CaCo₂O₄ belongs to an orthorhombic system (space group: Pnma) with lattice parameters, a=8.789(2) Å, b=2.9006(7) Å and c=10.282(3) Å. Curie-Weiss-like behavior in magnetic susceptibility with the nearly trivalent cobalt low-spin state (Co³⁺, 3d, S=0), semiconductor-like temperature dependence of resistivity (ρ=3×10⁻¹ Ω cm at 380 K) with dominant hopping conduction at low temperature, metallic-temperature-dependent large thermoelectric power (Seebeck coefficient: S=+147 μV/K at 380 K), and Schottky-type specific heat with a small Sommerfeld constant (γ=4.48(7) mJ/Co mol K²), were observed. These results suggest that the compound possesses a metallic electronic state with a small density of states at the Fermi level. The doped holes are localized at low temperatures due to disorder in the crystal. The carriers probably originate from slight off-stoichiometry of the phase. It was also found that S tends to increase even more beyond 380 K. The large S is possibly attributed to residual spin entropy and orbital degeneracy coupled with charges by strong electron correlation in the cobalt oxides.     

A one-dimensional organic-inorganic hybrid based on the bimolecular {[Cu(en)2]2[Cu2Si2W22O78]} polyoxometalate

A one-dimensional coordination polymer [Cu(en)₂]₂[Cu(en)₂(H₂O)]₂{[Cu(en)₂]₂[Cu₂Si₂W₂₂O₇₈]}·4.5H₂O (en=ethylenediamine), which represents the first example of one-dimensional organic-inorganic hybrid based on the bimolecular Keggin polyoxometalates {[Cu(en)₂]₂[Cu₂Si₂W₂₂O₇₈]}⁸⁻ has been hydrothermally synthesized and characterized by elemental analyses, IR, TG and single crystal X-ray diffraction. Crystal data: C₂₄H₈₅Cu₈N₂₄O_84.5Si₂W₂₂, monoclinic, P2₁/c, a=18.8126(3), b=23.0896(4), c=26.0711(4) Å, β=96.3790(10)°, V=11254.5(3) Å³, T=293(2) K; Z=4, μ=23.983 mm⁻¹, R₁=0.0628, wR₂=0.1210 [I>2σ], R₁=0.0854, wR₂=0.1285 (all data ).     

Investigations of new binary phosphate K4Ce2P4O15

The new potassium cerium(III) phosphate of formula K₄Ce₂P₄O₁₅ in the system Ce₂O₃-K₂O-P₂O₅ was prepared by solid state reactions and characterized by thermal analysis (DTA, TG, DSC), powder X-ray diffraction and IR spectroscopy. This compound exists only in the solid state (below 880 °C) and exhibits a polymorphic transition at 527 °C. The low-temperature form β-K₄Ce₂P₄O₁₅ of this compound crystallizes as a triclinic phase (space group P) with unit cell parameters: a=9.319(7), b=12.129(3), c=9.252(1) Å, α=106.875, β=100.086, γ=107.202°, V=916.276 Å³.     

Zr1−xLnxW2O8−x/2 (Ln=Eu, Er, Yb): Solid solutions of negative thermal expansion-synthesis, characterization and limited solid solubility

Zr_1−xLn_xW₂O_8−x/2 solid solutions (Ln=Eu, Er, Yb) of different substitution fractions x have been synthesized. Their X-ray diffraction (XRD) patterns have been indexed and lattice parameters calculated based on the α-ZrW₂O₈ structure. The coefficients of thermal expansion (CTEs) of these solid solutions were estimated to be −10.3×10⁻⁶ K⁻¹ in temperature range of 30-100 °C. The solubility of lanthanide ions in these solid solutions decreases linearly with the increase in the radius of substituted lanthanide ions. Based on the concentration dependence of phase transition temperatures, a novel method for determination of solubility of the lanthanide ions in Zr_1−xLn_xW₂O_8−x/2 solid solutions has been developed. This method seems to be more sensitive as compared with that based on XRD technique.