Infinite Tunnels Research Articles

Hydrothermal synthesis, crystal structure, thermal behaviour and magnetic properties of a new ammonium-chromium-iron(III) bis(hydrogenphosphate)

The hydrothermal synthesis and the chemical-physical characterization of an ammonium-chromium(III)-iron(III) bis(hydrogenphosphate), Cr0.34Fe0.66NH4(HPO4)2 [CrFeNP] is reported. It was obtained in aqueous media by reaction between chromium(III) chloride, iron(III) chloride, urea, and orthophosphoric acid. The crystal structure of CrFeNP was determined from single-crystal X-ray diffraction data. It crystallizes in the triclinic system, space group P-1, and exhibits two types of different infinite tunnels along [0 1 0] and [1 0 0] directions, where the ammonium cations are located. Thermal analysis shows that the solid is stable up to ca. 600 K. The activation energy of the thermal decomposition up to 1273 K was computed by isoconversional methods. In addition, the magnetic behaviour of the material was investigated from magnetic susceptibility and magnetization measurements. CrFeNP undergoes two successive magnetic transitions at temperatures TC=17.9 K and Tt=3.1 K, which could be related to a ferri- and an antiferromagnetic magnetic phase transitions, respectively.

Response of a circular tunnel embedded in saturated soil to a series of equidistant moving loads

The dynamic response of an infinitely long circular tunnel embedded in the saturated soil to a series of equidistant moving loads (SEML) is investigated in this study. The saturated soil surrounding the tunnel is described by Biot’s theory. Two scalar potentials and one vector potential are introduced to represent the displacement of the solid skeleton and the pore pressure. Based on Biot’s theory, the Helmholtz equations for the potentials are derived using the Fourier transform method. Performing the Fourier transform with respect to the longitudinal coordinate on the Helmholtz equations gives the frequency–wavenumber domain general solutions for the potentials. With the general solutions and the boundary conditions along the tunnel surface, the solution for the circular tunnel subjected to a single moving load (SML) is obtained. Superposition of the solutions for SMLs gives the representation for the response of the tunnel to a SEML, with which the resonance and cancelation conditions for the SEML are derived. Numerical simulations suggest that for the circular infinite tunnel there is a critical velocity. When the load moves with the critical velocity, the frequency domain response of the tunnel exhibits some dominant peak. Further, for a SEML moving with the critical velocity, the resonance and cancelation phenomena in the time domain may occur when the aforementioned resonance and cancelation conditions are fulfilled.

Sr21Bi8Cu2(CO3)2O41, a Bi5+ Oxycarbonate with an Original 10L Structure

The layered structure of Sr21Bi8Cu2(CO3)2O41 (Z = 2) was determined by transmission electron microscopy, infrared spectroscopy, and powder X-ray diffraction refinement in space group P63/mcm (No. 194), with a = 10.0966(3)Å and c = 26.3762(5)Å. This original 10L-type structure is built from two structural blocks, namely, [Sr15Bi6Cu2(CO3)O29] and [Sr6Bi2(CO3)O12]. The Bi5+ cations form [Bi2O10] dimers, whereas the Cu2+ and C atoms occupy infinite tunnels running along c⃗. The nature of the different blocks and layers is discussed with regard to the existing hexagonal layered compounds. Sr21Bi8Cu2(CO3)2O41 is insulating and paramagnetic.

Structure determination, electronic and optical properties of rubidium holmium polyphosphate RbHo(PO3)4

Structural, optical, and electronic properties of a new alkali metal-rare earth polyphosphate, RbHo(PO3)4, have been investigated by means of single-crystal X-ray diffraction, power X-ray diffraction, elemental analysis, and spectral measurement. RbHo(PO3)4 crystallizes in the monoclinic with space group P21/n and Z=4. It is described as a three-dimensional (3D) architecture built up of PO4 double spiral chains and HoO8 polyhedra by corner-sharing. The 11-coordinated rubidium atoms are located in infinite tunnels. Additionally, in order to gain further insight into the relationship between property and structure of RbHo(PO3)4, theoretical calculation based on the density functional theory (DFT) was performed using the total-energy code CASTEP.

Ambient rutile VO2(R) hollow hierarchitectures with rich grain boundaries from new-state nsutite-type VO2, displaying enhanced hydrogen adsorption behavior

Modulating the interaction between small gas molecules and solid host materials is becoming increasingly important for the future society due to the alternative energy resources especially for the hydrogen energy. As is known, two catalogues of materials such as two-dimensional (2D) lamellar cavity structures and three-dimensional (3D) infinite tunnel structures have received intensive considerations during the past decades. Herein, we put forward a new alternative that the solid materials with synergic effects of grain-boundary-rich (GBR) structure and 3D hierarchical hollow structure would also be a promising candidate for modulating the gas molecules in solid adsorbents. As expected, our constructed novel 3D hollow hierarchitectures with GBR shells standing on the hollow spherical cavity indeed resulted in the enhanced hydrogen adsorption behavior. The as-prepared 3D hollow hierarchitectures were very uniform in large scale, and the very simple reaction process offers high convenience, short reaction time, and no need for any complex manipulations or equipments. The hollow outlook of the rutile VO(2)(R) 3D hierarchitectures is the reminiscence of the hollow cavity of nsutite-type VO(2), while the formation of the VO(2)(R) GBR structure is attributed to volume shrink from a unique intergrowth structure of nsutite-type VO(2). The novel gas modulation model with the synergic effect of GBR structure and hierarchical hollow structure may pave a new way for developing materials in energy and environmental fields in the near future.

CsAlZr2(PO4)4: an anhydrous aluminium zirconium phosphate with a novel three-dimensional framework

Caesium aluminium dizirconium tetrakis[phosphate(V)], CsAlZr(2)(PO(4))(4), has been synthesized by high-temperature reaction and studied by single-crystal X-ray diffraction at room temperature. This represents the first detailed structural analysis of an anhydrous phosphate containing both zirconium and aluminium. The structure features a complicated three-dimensional framework of [AlZr(2)(PO(4))(4)] constructed by PO(4), AlO(4) and ZrO(6) polyhedra interconnected via corner-sharing O atoms, and one-dimensional Cs chains which are located in the infinite tunnels within the [AlZr(2)(PO(4))(4)] framework, which run along the c axis. The Cs, Al, one P and two O atoms lie on a mirror plane, while a second P atom lies on a twofold axis.

Two potassium rare-earth polyphosphates KLn(PO 3) 4 (Ln=Ce, Eu): Structural, optical, and electronic properties

Two potassium rare-earth polyphosphate single-crystals KLn(PO 3) 4 (Ln=Ce ( 1), Eu ( 2)) have been synthesized by the high-temperature solution reaction and characterized by single-crystal X-ray diffraction. The two isostructural compounds crystallize in the monoclinic system with space group P2 1, and all cell parameters shrink with the decrease of Ln 3+ ion radius. The main structural feature is (PO 3) 4 4− wavy chains and infinite tunnels delimited by LnO 8 and KO 8 polyhedra. The energy band structures, density of states (DOS), and optical response functions for 1 have been calculated with the density functional theory (DFT) method, and the dielectric functions and refractive indices have been discussed. The measurements of the absorption and emission spectra show that 1 exhibits the ultraviolet emissions, and 2 displays the characteristic yellow-red emissions of Eu 3+.

A p-Sulfonatothiacalix[4]arene Supramolecular Capsule Containing a Dinuclear Copper(II) Complex

The reaction of tetrasodium p-sulfonatothiacalix[4]arene (Na4H4TCAS), copper(II) nitrate and pyridine N-oxide (PNO) afforded a yellow copper(II)-p-sulfonatothiacalix[4]arene complex. X-ray diffraction analysis displays that it is an interesting dimeric supramolecular capsule, [Cu2(PNO)2(H2O)6]4+ ⊂ [(H6TCAS)2]4 − ·22H2O, in which two PNO molecules bridge the two CuII ions in the O,O′-μ2 mode and the hydrophobic aromatic rings point into the cavities of the thiacalixarenes. Interestingly, the thiacalixarenes pack themselves into the closed pores through π…π interactions in ab plane, and these pores further link to each other through hydrogen bonding to construct infinite hydrophilic tunnels, which fill with the disordered water molecules as the guests. In a dimeric supramolecular capsule, [Cu2(PNO)2 (H2O)6]4+ ⊂ [(H6TCAS)2]4·22H2O, two PNO molecules bridge the two CuII ions in the O,O′-μ2 mode and the hydrophobic aromatic rings point into the cavities of the thiacalixarenes. Interestingly, the thiacalixarenes pack themselves into the closed pores through π…π interactions in ab plane, and these pores further link to each other through hydrogen bonding to construct infinite hydrophilic tunnels, which fill with the disordered water molecules as the guests.

Synthesis and characterization of half-sandwich iridium complexes containing 2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene and ancillary ortho-carborane-1,2-dichalcogenolato ligands

The binuclear half-sandwich iridium complexes {Cp ∗IrCl 2} 2(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) ( 3) and {Cp ∗Ir[E 2C 2(B 10H 10)]} 2(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (E = S( 5a), Se( 5b)) were prepared from the reaction of [Cp ∗IrCl(μ-Cl)] 2 or the “ pseudo-aromatic” half-sandwich iridium complex Cp ∗Ir[E 2C 2(B 10H 10)] (E = S( 4a), Se( 4b)) with a tetrathiafulvalene (TTF) derivative 2,6-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene ( 2) at room temperature. The complexes ( 3, 5a and 5b) have been fully characterized by IR and NMR spectroscopy, as well as elemental analysis. And the molecular structures of 2 and 5a were established through X-ray crystallography. It is interesting that infinite tunnels are created by repeating ‘buckled bowl’ molecules of 5a.

Intermetallic Compounds with 1D Infinite Tunnels. Syntheses and Structures of AAu4In2 (A: K, Rb).

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Intermetallic Compounds with 1D Infinite Tunnels. Syntheses and Structures of AAu4In2 (A = K, Rb)

Four intermetallic compounds KxRb1-xAu4In2 (x = 0-1) synthesized by high-temperature solid-state reactions display 1D infinite tunnel constructions with Au-In frameworks. These compounds show small but different cation displacements in the tunnels and are also air and moisture inert at room temperature, even in concentrated HCl(aq).

Crystal structure of ErAlGeO 5 and evidence of a peculiar double coordination sphere of Al(III) and Ge(IV) cations

Single crystals of a new erbium alumino-germanate with gross formula ErAlGeO 5 have been isolated, using the flux method. The structure determined from X-ray single crystal diffraction data, was refined with the space group Pmcb (No 55), a = 5.580 ( 1 ) Å , b = 7.208 ( 1 ) Å , c = 8.309 ( 2 ) Å , Z = 4 , D calc = 3.326 g ⋅ cm −1 , R 1 = 4.29 % ; w R 2 = 11.76 % ). When regarded along [100], the structure can be seen as made of rutile chains of the type [(Ge,Al)O 2] connected by pairs of [(Ge,Al)O 5] pyramids, arranged in the manner to delimit infinite tunnels with pentagonal sections, running parallel to [100] and filled by erbium ions. The close coordination spheres of Er(III) cations can be viewed as a bicapped trigonal prism. Due to the cationic distribution of both Al 3+ and Ge 4+ ions on the same octahedral and pyramidal centres, the crystal chemical formula of the title compound can be written as: Er(Al 0.73Ge 0.27)(Ge 0.73Al 0.27)O 5. The crystallographic data of the present study have evidenced two original characteristics of the resolved structure: (i) pentavalent coordination of both Al 3+ and Ge 4+ ions; (ii) location of Ge 4+ ion in an octahedral environment, which is unusual for this cation under normal pressure.

Synthesis and crystal structures of (NH 3CH 2CH 2NH 3) 1.5[(VO) 2(HPO 4) 2(PO 4)] and (C 4H 12N 2) 2[V 4O 6H(HPO 4) 2(PO 4) 2], two layered vanadium phosphates templated with organic diamines

Two new layered vanadium phosphates templated by ethylenediamine, (NH 3CH 2CH 2NH 3) 1.5[(VO) 2(HPO 4) 2(PO 4)] ( 1), and piperazine, (C 4H 12N 2) 2[V 4O 6H(HPO 4) 2(PO 4) 2] ( 2), have been synthesized hydrothermally and their structures determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group C2/c (no. 15) with a=18.6051(5), b=7.1193(1), c=23.4597(7) Å, β=96.558(2)°, V=3087.03 Å 3, Z=8, and R1=0.0583. The structure consists of infinite chains of trans-corner-shared VO 6 octahedra, which are bridged by phosphate groups. The infinite chains are connected by VO 5 square pyramids via V–O–P bonds to form layers with 10-sided windows. Adjacent layers are aligned such that infinite tunnels along the [001] direction are generated. Ethylenediammonium cations are located at sites both in the interlayer space and in the windows within the layers. Crystal data for 2: orthorhombic, space group Pna2 1 (no. 33), a=13.1812(6), b=15.2918(8), c=6.2821(3) Å, V=1266.25 Å 3, Z=2, and R1=0.0367. Compound 2 is a mixed-valence V IV/V V vanadium phosphate as was confirmed by magnetic susceptibility measurements. V IVO 6 octahedra connected via HPO 4 groups form a double chain, which alternates with a chain of trans-corner-shared square pyramids containing an infinite V IV–O–V V–O motif. Both chains are connected through phosphate groups to form a layer, which contains 14-membered empty windows. Piperazinium dications are anchored in the interlayer space.

Peierls transitions in quasi-one-dimensional conductor Nb3Te4and the effect of metal–atom intercalation, investigated by93Nb magnetic resonance

We have carried out a 93Nb nuclear magnetic resonance (NMR) study on a quasi-one-dimensionalsuperconductor, Nb3Te4, and the isostructural intercalated compounds AxNb3Te4 (A = Inand Zn), to understand the varied impact of metal–atom intercalationsinto the hexagonal infinite tunnels on the charge density wave andsuperconductivity formations. Below the Peierls transition temperature TCfor each of the compounds, the nuclear spin–lattice relaxation rate(T1 T)−1exhibited a significant decrease which originates from the partialFermi surface quenching associated with the Peierls transition. Withx ≃ 0.1 introductionsof In and Zn, (T1 T)−1was greatly enhanced from 10 s−1K−1 to 20 and 18 s−1K−1, respectively.On the other hand, the nuclear quadrupole frequency νQwas diminished from 0.98 MHz to 0.63 and 0.74 MHz, respectively.A remarkable difference between the In and Zn intercalations wasfound in the extent of decrease in the isotropic Knight shift Kiso:from 0.237 to 0.216% for In; and to 0.166% for Zn. Based upon the d bandstructures predicted theoretically, we have indicated that the variations in theNMR parameters can be explained consistently, if the extent of hole dopingby a Zn atom is much larger than that by an In atom. The heavy holedoping by Zn intercalation changes the dominant subband at EF from dyz,zx to dx2 −y2,giving rise to a distinct nesting condition of the Fermi surface.

Synthesis and structure of (H3NC2H4NH3)2Co7(PO4)6: a novel open framework cobalt phosphate.

The hydrothermally synthesized [H3NC2H4HN3]2Co7(PO4)6 has an open framework structure built from four-, five- and six-coordinated cobalt atoms and PO4 tetrahedra, which forms infinite tunnels of 12-membered rings housing ethylenediammonium cations.

ELASTIC AND INELASTIC RESPONSE OF TUNNELS UNDER LONGITUDINAL EARTHQUAKE EXCITATION

This paper addresses the problem of the behaviour of underground tunnels subjected to longitudinal earthquake excitation. State-of-the-art solutions, which are relative to infinite length tunnels in the stationary case, with linear models for both the ground and the structure, are first recalled. These models are either static or dynamic; results generally indicate large strains, often incompatible with reinforced concrete structures, and small crack widths. For finite length tunnels, in this study the dynamic solution for the linear case is developed and it is shown that maximum strain is an increasing function of the tunnel length so that, in many situations, the behavior of the lining is satisfactory also under the aspect of crack formation. When the nonlinear behaviors of the tunnel and soil are taken into account, segments of reinforced concrete tunnels, after cracking, may undergo considerable relative displacement, undesired both for serviceability and ultimate limit states. After review of the constitutive relationship for the ground, a parametric study on the crack openings for an example tunnel is presented. It is shown that crack widths computed with linear static analyses underestimate the real value for tunnels embedded in stiff grounds and that the lining longitudinal reinforcement can reduce crack width so as to cope with serviceability and ultimate limit states.

An Integral Equation Method for the Flow in an Infinite Tunnel

The steady plane irrotational incompressible parallel flow in an infinite tunnel with an obstacle (e.g. an airfoil) is studied. The boundary value problem (BVP) admits the treatment by the boundary integral equation method (BIEM) that transforms the BVP to an integral equation with boundary integral operators. Since these operators are neither compact nor of Fredholm. type, existence and uniqueness results cannot be derived from Fredholm's theory and numerical problems occur because the domain is unbounded. To overcome these difficulties the BVP is transformed to a finite ring-domain. The parallel flow in the tunnel is transformed to the flow of a source/sink system in the ring-domain. Using BIEM for the transformed problem we obtain an integral equation with a compact linear operator. A procedure for computation of the numerical solution is derived by a Nystrom-like method with simple quadrature rules. Engineers are interested in the tangential component of the flor around the obstacle. We do this job in the ring-domain and re-transform the results for the original obstacle.

Structure Cristalline du Diphosphate SrCuP 2O 7

The structure of SrCuP 2O 7 is isostructural with that of CaCuP 2O 7 and related to that of α-Ca 2P 2O 7. SrCuP 2O 7 crystallizes in the monoclinic space group P 2 1/ n with lattice parameters a = 12.455(2) Å, b = 8.129(1) Å, c = 5.369(1) Å, and β = 90.59(1)°. A total of 1386 independent reflections ( I ≥ 3 σ( I)) have been used to refine the structure to R = 0.046 ( R w = 0.044). The mixed framework of the structure is built up with CuO 5 and P 2O 7 units which define infinite tunnels along [001] direction where strontium atoms are located. Copper ions occupy isolated square pyramidal sites.

Reexamination of the Crystal Structure of Na3Sb7O9Se3·Sb0.319(H2O,OH)3

Abstract The crystal structure of Na3Sb7O9Se3·Sb0.319(H2O,OH)3 has been determined using a single crystal prepared by hydrothermal synthesis to a conventional R = 0.043, Rw = 0.039 for 1556 reflections. It is hexagonal with a space group of P63; a = 14.422(4), c = 5.5448(8) Å, Z = 2. The structure consists of infinite tunnels formed by the linkages of SbO3 pyramids. SbSe3 pyramids among the tunnels connect the tunnels to form a three-dimensional structure. Na atoms were on the inside wall of the tunnel. It was revealed that statistically occupied Sb(H2O,OH)6-octahedra are located at the center of the tunnel. Two statistical sites for the Sb atom of the SbSe3 pyramids are pointed out.

Centrifuge Study of Faulting Effects on Tunnel

If a tunnel crosses a geological fault which is considered to be active, the possibility of a displacement in the fault must be accounted for in the tunnel design. When the tunnel is embedded in soil, the assessment of the effect of the fault movement is not easy to assess. As a guide to analysis, a series of correctly scaled model experiments in a centrifuge is undertaken. The deflections and stresses induced in a tunnel crossing a fault caused by: (a) Fault displacement; and (b) differential earthquake motions across the fault are quantified by a series of centrifuge tests on a finite length model tunnel. The centrifuge results are used to calibrate a one‐dimensional finite element model of the tunnel for soil‐tunnel interaction effects. The numerical model is then used to predict the response of an essentially infinite length tunnel for design purposes. Bending movements, displacements and shears are displayed. Surprisingly small changes in the bending movements from the finite‐length to the infinite tunnel case are obtained.