A disorder-enhanced quasi-one-dimensional superconductor.

A powerful approach to analysing quantum systems with dimensionality d>1 involves adding a weak coupling to an array of one-dimensional (1D) chains. The resultant quasi-1D (q1D) systems can exhibit long-range order at low temperature, but are heavily influenced by interactions and disorder due to their large anisotropies. Real q1D materials are therefore ideal candidates not only to provoke, test and refine theories of strongly correlated matter, but also to search for unusual emergent electronic phases. Here we report the unprecedented enhancement of a superconducting instability by disorder in single crystals of Na2-δMo6Se6, a q1D superconductor comprising MoSe chains weakly coupled by Na atoms. We argue that disorder-enhanced Coulomb pair-breaking (which usually destroys superconductivity) may be averted due to a screened long-range Coulomb repulsion intrinsic to disordered q1D materials. Our results illustrate the capability of disorder to tune and induce new correlated electron physics in low-dimensional materials.

Na4.25Mo15S19: a novel ternary reduced molybdenum sulfide containing Mo6 and Mo9 clusters.

The structure of tetra-sodium penta-deca-molybdenum nona-deca-sulfide, Na4.25Mo15S19, is isotypic with Na3.9Mo15Se19 [Salloum et al. (2013 ▶). Acta Cryst. E69, i67-i68]. It is characterized by Mo6S (i) 8S (a) 6 and Mo9S (i) 11S (a) 6 (where i represents inner and a apical atoms) cluster units that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c, and have point-group symmetry -3 and -6, respectively. The clusters are inter-connected through additional Mo-S bonds. The Na(+) cations occupy inter-unit voids formed by six or seven S atoms. One Mo, one S and one Na site [occupancy 0.751 (12)] are situated on mirror planes, and two other S atoms and one Na site (full occupancy) are situated on threefold rotation axes.

The pro-inflammatory cytokines IL-1ß and TNFα are neurotrophic for enteric neurons.

Intestinal inflammation causes initial axonal degeneration and neuronal death but subsequent axon outgrowth from surviving neurons restores innervation density to the target smooth muscle cells. Elsewhere, the pro-inflammatory cytokines TNFα and IL-1ß cause neurotoxicity, leading us to test their role in promoting enteric neuron death. In a rat coculture model, TNFα or IL-1ß did not affect neuron number but did promote significant neurite outgrowth to twofold that of control by 48 h, while other cytokines (e.g., IL-4, TGFß) were without effect. TNFα or IL-1ß activated the NFκB signaling pathway, and inhibition of NFκB signaling blocked the stimulation of neurite growth. However, nuclear translocation of NFκB in smooth muscle cells but not in adjacent neurons suggested a dominant role for smooth muscle cells. TNFα or IL-1ß sharply increased both mRNA and protein for GDNF, while the neurotrophic effects of TNFα or IL-1ß were blocked by the RET-receptor blocker vandetanib. Conditioned medium from cytokine-treated smooth muscle cells mimicked the neurotrophic effect, inferring that TNFα and IL-1ß promote neurite growth through NFκB-dependent induction of glial cell line-derived neurotrophic factor (GDNF) expression in intestinal smooth muscle cells. In vivo, TNBS-colitis caused early nuclear translocation of NFκB in smooth muscle cells. Conditioned medium from the intact smooth muscle of the inflamed colon caused a 2.5-fold increase in neurite number in cocultures, while Western blotting showed a substantial increase in GDNF protein. Pro-inflammatory cytokines promote neurite growth through upregulation of GDNF, a novel process that may facilitate re-innervation of smooth muscle cells and a return to homeostasis following initial damage.

Multiband superconductivity in the Chevrel phases SnMo6S8 and PbMo6S8.

Sub-Kelvin scanning tunneling spectroscopy in the Chevrel phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Δ1=3 meV, Δ2∼1.0 meV and Δ1=3.1 meV, Δ2∼1.4 meV, respectively. The gap distribution is strongly anisotropic, with Δ2 predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well fitted by an anisotropic two-band BCS s-wave gap function. Our spectroscopic data are confirmed by electronic heat capacity measurements, which also provide evidence for a twin-gap scenario.

Ag(2.54)Tl(2)Mo(12)Se(15): a new structure type containing Mo(6) and Mo(9) clusters.

The novel structure-type Ag(2.54)Tl(2)Mo(12)Se(15) (silver thallium molybdenum selenide) is built up of Mo(6)Se(i)(8)Se(a)(6) and Mo(9)Se(i)(11)Se(a)(6) cluster units in a 1:2 ratio, which are three-dimensionally connected to form the Mo-Se network. The Ag and Tl cations are distributed in several voids within the cluster network. Three of the seven independent Se atoms and one Tl atom lie on sites with 3.. symmetry (Wyckoff sites 2c or 2d).

Synthesis, crystal structures, and physical properties of the novel Ca(x)R(17-x)Mo19O46 (4 < or = x < or = 7; R = Ce, Pr, Sm, and Gd) compounds containing centered Mo19 nu2-octahedral clusters.

The novel quaternary reduced molybdenum oxides Ca(x)R(17-x)Mo(19)O(46) (4 < or = x < or = 7; R = Ce, Pr, Sm, and Gd) have been synthesized by a solid-state reaction at 1400 degrees C for 48 h in sealed molybdenum crucibles. The crystal structure was determined on a single crystal of Ca(5.24)R(11.76)Mo(19)O(46) by X-ray diffraction. This compound crystallizes in the monoclinic space group C2/m: a = 19.5192(4) A, b = 11.1244(3) A, c = 13.2589(5) A, beta = 132.055(1) degrees, V = 2137.7(1) A(3), Z = 2. Refinements yield R1(F(2)) = 0.0388 and wR2(F(2)) = 0.0792 for 5667 unique reflections. The structure is built up from alternating slabs made up of Mo forming centered Mo(19) nu(2)-octahedral clusters, Ca, Pr, and O atoms and slabs containing only Ca, Pr, and O atoms. The Mo(19) cluster, in which the Mo-Mo distances range from 2.7274(4) to 2.7940(7) A, results from a three-dimensional condensation of six Mo(6) octahedra. The Ca(2+) and Pr(3+) cations occupy seven crystallographically independent sites with coordination numbers in the O atoms varying from 6 to 8. Magnetic susceptibility measurements made on the Ca(x)Pr(17-x)Mo(19)O(46) (x = 4-7) compounds confirm the presence of Pr(3+) cations, and no magnetic ordering was observed down to 4.2 K. Electrical resistivity measurements on a single crystal of Ca(approximately 5)Pr(approximately 12)Mo(19)O(46) show a semiconducting behavior.

Cr1.45Tl1.87Mo15Se19, a monoclinic variant of the hexagonal In3Mo15Se19 type.

The monoclinic compound Cr(1.45)Tl(1.87)Mo(15)Se(19) (chromium thallium pentadecamolybdenum nonadecaselenide) represents a variant of the hexagonal In(3)Mo(15)Se(19) structure type. Its crystal structure consists of an equal mixture of Mo(6)Se(8)Se(6) and Mo(9)Se(11)Se(6) cluster units. The Mo and Se atoms of the median plane of the Mo(9)Se(11)Se(6) unit, as well as three Cr ions, lie on sites with m symmetry (Wyckoff site 2e). The fourth Cr ion is in a 2b Wyckoff position with 1 site symmetry.

Synthesis, crystal and electronic structures, and physical properties of the novel compounds LaR4Mo36O52 (R = Dy, Er, Yb, and Y) containing infinite chains of trans-edge-shared Mo6 octahedra and Mo2 pairs and rectangular Mo4 clusters with triple Mo-Mo bonds.

The novel quaternary reduced molybdenum oxides LaR(4)Mo(36)O(52) (R = Dy, Er, Yb, and Y) have been synthesized with solid-state reactions at 1400 degrees C for 48 h in sealed molybdenum crucibles. The crystal structure was determined on a single crystal of LaEr(4)Mo(36)O(52) by X-ray diffraction. LaEr(4)Mo(36)O(52) crystallizes in the tetragonal space group I4 with two formula units per cell and the following lattice parameters: a = 19.8348(2) and c = 5.6594(1) A. The Mo network is dominated by infinite chains of trans-edge-shared Mo(6) octahedra, which coexist with Mo(2) pairs and rectangular Mo(4) clusters. The Mo-Mo distances within the infinite chains range from 2.5967(7) to 2.8529(8) A and from 2.239(3) to 2.667(2) A in the Mo(2) pairs and rectangular Mo(4) clusters, respectively. The Mo-O distances are comprised between 1.993(7) and 2.149(7) A, as usually observed in these types of compound. The La(3+) and Er(3+) ions are in a square-prismatic [LaO(8)] and a tricapped trigonal-prismatic [ErO(9)] environment of oxygen atoms, respectively. The La-O distances range from 2.555(6) to 2.719(6) A and the Er-O ones from 2.260(6) to 2.469(5) A. Theoretical calculations allow the determination of the optimal electron count of both motifs in the title compound. Weak interactions occur between neighboring dimetallic and tetrametallic clusters and between trans-edge-sharing infinite chains and dimers and tetramers. The presence of rectangular clusters is favored on the basis of theoretical considerations. Single-crystal resistivity measurements show that LaEr(4)Mo(36)O(52) is metallic between 4.2 and 300 K, in agreement with the band structure calculations. Magnetic susceptibility measurements indicate that the oxidation state of the magnetic rare earths is +3, and there is an absence of localized moments on the Mo network.

Real-space vortex glass imaging and the vortex phase diagram of SnMo6S8.

Using scanning tunneling microscopy at 400 mK, we have obtained maps of around 100 vortices in SnMo(6)S(8) from 2-9 T. The orientational and positional disorder at 5 and 9 T show that these are the first large-scale images of a vortex glass. At higher temperature a magnetization peak effect is observed, whose upper boundary coincides with a lambda anomaly in the specific heat. Our data favor a kinetic glass description of the vortex melting transition, indicating that vortex topological disorder persists at fields and temperatures far below the peak effect in low-T(c) superconductors.

The disordered cluster compound CaMo5(Mo0.38Ti0.62)O10.

The title compound, calcium pentamolybdenum titanium decaoxide, is isomorphous with the AMo(5)(Ti(0.7)Mo(0.3))O(10) (A = Sr and Eu) compounds. The smaller size of calcium induces a higher molybdenum content on the capping sites of the bioctahedral Mo(10) clusters, leading to more Mo(11) and Mo(12) clusters in the crystal structure. The oxygen framework derives from the stacking of close-packed layers along the a direction in the ...ABAC... sequence. The Ca(2+) ions occupy large cavities which result from the fusion of two cubooctahedra and are surrounded by ten O atoms. The Ti(4+) ion is octahedrally coordinated by the O atoms.

The pyrochlore-type molybdate Pr(1.37)Ca(0.63)Mo(2)O(7).

Praseodymium calcium dimolybdenum hepta-oxide, Pr(1.37)Ca(0.63)Mo(2)O(7), crystallizes in the cubic pyrochlore-type structure. In the crystal structure, MoO(6) octa-hedra are linked together by common corners, forming a three-dimensional [Mo(2)O(6)] network. The Pr and Ca atoms and the remaining O atoms are located in the voids of the [Mo(2)O(6)] network. The Pr and Ca atoms are distributed statistically over the same 16c crystallographic position with site-occupancy factors of 0.684 (3) and 0.316 (3), respectively. They are surrounded by eight O atoms forming a ditrigonal scalenohedron. All atoms lie on special positions. The (Pr, Ca) and Mo atoms are, respectively in the 16c and 16d positions with m symmetry, and the O atoms in the 48f or 8a positions with mm or 3m site symmetry, respectively.

Rare-earth site splitting in Sm3MoO7.

Trisamarium molybdenum heptaoxide, Sm(3)MoO(7), is isomorphous with Ln(3)MoO(7) (Ln = La and Pr). The crystal structure consists of chains of corner-linked MoO(6) octahedra running parallel to the b axis and separated from each other by seven- or eight-coordinate Sm-O polyhedra. In contrast to La(3)MoO(7) and Pr(3)MoO(7), a splitting of one Sm site into two positions is observed.

La5Mo6O21: a novel ternary reduced molybdenum oxide containing {MoIV}3 clusters and isolated MoV centres.

The crystal structure of La5Mo6O21 (pentalanthanum hexamolybdenum henicosaoxide) is made up of Mo3O13 units containing triangular {MoIV}3 clusters, three distorted MoVO6 octahedral units and six interstitial LaIII atoms. The Mo3O13 unit consists of three edge-sharing MoIVO6 units involving Mo-Mo bonding. The three MoVO6 octahedra share their corners or edges with each other and with the Mo3O13 units.

Cs2Mo15S19: a novel ternary reduced molybdenum sulfide containing Mo6 and Mo9 clusters.

The crystal structure of dicaesium pentadecamolybdenum nonadecasulfide, Cs(2)Mo(15)S(19), consists of a mixture of Mo(6)S(8)S(6) and Mo(9)S(11)S(6) cluster units in a 1:1 ratio. Both units are interconnected via inter-unit Mo-S bonds. The Cs(+) cations occupy large voids between the different cluster units. The Cs and two inner S atoms lie on sites with 3 symmetry (Wyckoff site 12c) and the Mo and S atoms of the median plane of the Mo(9)S(11)S(6) cluster unit on sites with 2 symmetry (Wyckoff site 18e).

Cs(6)Mo(27)S(31): a novel ternary reduced molybdenum sulfide containing Mo(9) and Mo(18) clusters.

The crystal structure of hexacaesium heptacosamolybdenum hentriacontasulfide, Cs(6)Mo(27)S(31), consists of a mixture of Mo(9)S(11)S(6) and Mo(18)S(20)S(6) cluster units in a 1:1 ratio. The units are connected through Mo-S bonds. Cs(+) cations occupy large voids between the different cluster units.

Structural trends and the electronic structure of the rare-earth oxomolybdates RMo(5)O(8) (R = La, Ce, Pr, Nd, Sm, Eu and Gd) containing chains of bioctahedral Mo(10) clusters.

The crystal structures of the rare-earth members of the series RMo(5)O(8) (R = Ce to Eu) have been investigated and compared with those of the La and Gd members previously published in order to understand the influences of the size and the charge of the cation on the different Mo-Mo bonds. The RMo(5)O(8) compounds crystallize in the monoclinic space group P2(1)/c. Their crystal structure is characterized by bioctahedral Mo(10) clusters forming extended chains. The results of our single-crystal studies show that the modification of charge predominantly affects the Mo-Mo bonds between the Mo(10) clusters and, to a lesser extent, the intra-cluster distances, while the cationic size induces only small variations. Theoretical investigations confirm this statement and allow the understanding of the bonding mode in these compounds.

Synthesis, structural trends, and physical and electronic properties of the reduced molybdenum oxides R(4)Mo(4)O(11) (R = Nd-Tm and Y) containing infinite chains of trans-edge-shared octahedral clusters.

The new compounds R(4)Mo(4)O(11) (R = Y, Nd, Sm-Tm) have been synthesized as crystalline powders by solid-state reaction in a sealed molybdenum crucible at 1400 degrees C. Single crystals suitable for X-ray structure determinations and resistivity measurements were also prepared. The R(4)Mo(4)O(11) compounds crystallize in the orthorhombic space group Pbam with four formulas per unit cell. The crystal structure of these compounds is based on infinite chains of trans-edge-shared molybdenum octahedra, which are widely separated by the rare-earth cations that are in monocapped trigonal prismatic coordination of oxygen atoms. Consequently, adjacent metallic chains do not share oxygen atoms and the shortest interchain Mo-Mo distance is greater than 7 A. Within the infinite chains, a strong pairing between the apical Mo atoms occurs, leading to a pattern of alternating short and long distances between these atoms. Resistivity measurements on single crystals show that the R(4)Mo(4)O(11) compounds are small band gap semiconductors, and magnetic susceptibility studies are in agreement with the presence of R(3+) ions. In addition, antiferromagnetic orderings have also been observed for the R(4)Mo(4)O(11) compounds with R = Gd-Tm below 5 K. Theoretical calculations confirm the stabilization of the structure by the distortion and agree with the resistivity and magnetic measurements.

Rb5Mo27Se31, a novel ternary reduced molybdenum selenide containing Mo12 and Mo15 clusters.

The crystal structure of Rb5Mo27Se31, pentarubidium heptacosamolybdenum hentriacontaselenium, consists of a mixture of Mo12Se14Se6 and Mo15Se17Se6 cluster units in a 1:1 ratio. Both types of cluster are interconnected through inter-unit Mo-Se bonds. Rb+ cations occupy large voids between the different cluster units.

MTi(0.7)Mo(0.3)Mo(5)O(10) (M = SR, Eu), first evidence of mono- and bicapped bioctahedral Mo(11) and Mo(12) clusters: synthesis, crystal structures, and physical properties.

The novel quaternary reduced molybdenum oxides MTi(0.7)Mo(0.3)Mo(5)O(10) (M = Sr, Eu) have been synthesized by solid-state reaction at 1400 degrees C for 48 h in sealed molybdenum crucibles. Their crystal structures were determined on single crystals by X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pbca with 8 formula units per cell and the following lattice parameters: a(Sr) = 9.1085 (7), b(Sr) = 11.418 (1), and c(Sr) = 15.092 (3) A; a(Eu) = 9.1069 (7), b(Eu) = 11.421 (2), and c(Eu) = 15.075 (1) A. The Mo network is dominated by bioctahedral Mo(10) clusters, which coexist randomly with Mo(11) and Mo(12) clusters (monocapped and bicapped Mo(10) clusters). The Mo-Mo distances within the clusters range from 2.62 to 2.92 A and the Mo-O distances from 1.99 to 2.17 A as usually observed in the reduced molybdenum oxides. The Sr(2+) and Eu(2+) ions occupy large cavities, which result from the fusion of two cubooctahedra and thus are surrounded by 11 oxygen atoms. The M-O distances range from 2.50 to 3.23 A for the Sr compound and from 2.49 to 3.24 A for the Eu analogue. Single-crystal resistivity measurements indicate that both materials are poor metals with transitions to semiconducting states below 50 and 40 K and room temperature resistivity values of 9 x 10(-3) and 5 x 10(-3) Omega.cm for the Sr and Eu compounds, respectively. The magnetic susceptibility data indicate paramagnetic behavior due to the Eu(2+) moment at high temperatures for the Eu compound and do not reveal the existence of localized moments on the Mo and Ti sublattice in the Sr compound. An XPS study clearly suggests that the isolated Ti ions are tetravalent. Theoretical considerations preclude the existence of heterometallic Mo-Ti clusters.

Rb4Mo21Se24 containing Mo12 and Mo15 clusters.

Rubidium molybdenum selenide, Rb(4)Mo(21)Se(24), crystallizes in the trigonal space group R-3. Its crystal structure consists of a mixture of Mo(12)Se(14)Se(6) and Mo(15)Se(17)Se(6) cluster units in a 1:2 ratio. Both units are interconnected through Mo-Se bonds. The Rb(+) cations occupy large voids between the different cluster units.