The composite material based on Dawson-type polyoxometalate and activated carbon as the supercapacitor electrode

A supercapacitor electrode assembled from activated carbon (AC) and (NH₄)₆[P₂Mo₁₈O₆₂]·14.2H₂O (P₂Mo₁₈) was fabricated for the first time, and showed remarkable electrochemical performance ascribed to the synergy of the double layer capacitance of AC and the pseudocapacitance of P₂Mo₁₈. The investigations indicate that the AC/P₂Mo₁₈ electrode exhibits a specific capacitance of 275 F g^− 1 at a high current density of 6 A g^− 1, which is substantially larger than the 182 F g^− 1 of the AC electrode. In addition, the AC/P₂Mo₁₈ electrode possesses a remarkable rate capability (89%) when the current density is increased from 2 to 6 A g^− 1.     

Ionic conductivities and phase transitions of lanthanide rare-earth substituted La2Mo2O9

The ion conductivities and phase transitions of lanthanum molybdate (La₂Mo₂O₉) substituted with lanthanide rare-earths are investigated using impedance spectroscopy, dilatometry, and X-ray powder diffraction. Among the substituted La₂Mo₂O₉ of 10 mol% Ce, Nd, Sm, Gd, Dy, Er, Yb, the specimens containing Er, and Dy exhibit depressed α–β phase transformation and high conductivities. Their 700 °C conductivities are approximately five to seven times that of La₂Mo₂O₉, around 0.26 S cm⁻¹, comparable with those of (LaSr)(GaMg)O₃ and Gd-substituted CeO₂. Among the three compositions of 10 mol% Gd, Dy, Er showing depressed phase transition, Er- and Dy-substituted La₂Mo₂O₉ possess relatively low thermal expansion coefficient 11×10⁻⁶ K⁻¹, compared with that of the Gd-substituted La₂Mo₂O₉, 18×10⁻⁶ K⁻¹, which is near that of La₂Mo₂O₉. Hence, Dy and Er are valuable dopants in improving the La₂Mo₂O₉ properties. Across the lanthanide series, 10 mol%-substituted La₂Mo₂O₉ demonstrates systematic variations in the conductivity–temperature relation. Hysteresis phenomena in both of conductivity and thermal expansion are also observed in those compositions which display phase transition.     

Electrical conductivity of Mo6S3I6 and Mo6S4.5I4.5 nanowires

Electrical conductivity measurements on novel materials composed of bundles of Mo₆S₃I₆ and Mo₆S_4.5I_4.5 nanowires pressed in a sheet form, in the frequency range from 10 Hz to 1 MHz for temperatures between 4 K and 330 K, are reported. Temperature dependence of the quasistatic electrical conductivity show similar dependence at higher temperatures as expected for three-dimensional variable range hopping mechanism with decreasing electrical conductivity as temperature decreases. Below 50 K the electrical conductivity becomes completely temperature independent. It seems that at lower temperatures fluctuation-induced tunnelling mechanism dominates in these nanostructured materials.     

KSbI6O18: An antimony iodate semiconductor material with cyclic chiral S6-symmetric hexaiodate

The antimony iodate KSbI₆O₁₈ which contains cyclic S₆-symmetric chiral hexaiodate has been successfully synthesized through hydrothermal reaction. It crystallizes in trigonal space group R-3 with cell parameters of a = 11.3057(6) Å, c = 11.3340(8) Å, γ = 120° and z = 3. Six corner-shared IO₄ groups form cyclic S₆-symmetric chiral I₆O₁₈ groups that are linked by Sb^5 + to form anionic [Sb(I₆O₁₈)]⁻ framework with cavities filled by K⁺ ions. Optical diffuse reflectance spectra indicate that KSbI₆O₁₈ is a potential semiconductor with optical band gap of 2.96 eV.     

Quantum chemical study of the addition effect on the geometry of the [Mo6S8(CN)6]6− cluster

The geometrical structure and bonding in adducts [Mo₆S₈(CN)₁₂ · Cr(CO)₄L]⁶⁻ (L = CO, PH₃, PF₃, P(OCH₃)₃) were studied on the base of quantum chemical calculations. The main attention was paid to the study of the changes in the cluster geometry under the influence of the attached Cr(CO)₄L group. The large deformations in the Mo₆ core were found and explained by the electrostatic interaction and the pseudo-Jhan–Teller effect. The high values of the calculated polarizabilities of the compounds under consideration are in accord with the obtained results.     

Electrical properties of a-C: Mo films produced by dual-cathode filtered cathodic arc plasma deposition

Molybdenum-containing amorphous carbon (a-C:Mo) thin films were prepared using a dual-cathode filtered cathodic arc plasma source with a molybdenum and a carbon (graphite) cathode. The Mo content in the films was controlled by varying the deposition pulse ratio of Mo and C. Film sheet resistance was measured in situ at process temperature, which was close to room temperature, as well as ex situ as a function of temperature (300–515 K) in ambient air. Film resistivity and electrical activation energy were derived for different Mo and C ratios and substrate bias. Film thickness was in the range 8–28 nm. Film resistivity varied from 3.55 × 10^− 4 Ω m to 2.27 × 10^− 6 Ω m when the Mo/C pulse ratio was increased from 0.05 to 0.4, with no substrate bias applied. With carbon-selective bias, the film resistivity was in the range of 4.59 × 10^− 2 and 4.05 Ω m at a Mo/C pulse ratio of 0.05. The electrical activation energy decreased from 3.80 × 10^− 2 to 3.36 × 10^− 4 eV when the Mo/C pulse ratio was increased in the absence of bias, and from 0.19 to 0.14 eV for carbon-selective bias conditions. The resistivity of the film shifts systematically with the amounts of Mo and upon application of substrate bias voltage. The intensity ratio of the Raman D-peak and G-peak (I_D/I_G) correlated with the pre-exponential factor (σ₀) which included charge carrier density and density of states.     

Synthesis,structure, and substitution reactivity of a new bi-oxo capped molybdenum cluster: [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+

A new bi-oxo capped molybdenum carboxylate, [Mo₃(μ₃-O)₂(μ-O₂CCH₂Cl)₆(H₂O)₂(OH)]⁺, was synthesized by refluxing [Mo₃(μ₃-O)₂(μ-O₂CCH₃)₆(H₂O)₃]^2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO₄ eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d₄, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is k_obs^298K = 5.3 × 10^− 5 (± 0.3) s^− 1 and activation parameters equal to ΔH³ = 130 (± 10) kJ mol^− 1 and ΔS³ = 111 (± 33) J mol^− 1 K^− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands.     

Relationship between mechanical properties and coefficient of friction of sputtered a-C/Cu composite thin films

The article reports on properties of a-C films containing different amount of Cu. Films were sputtered by unbalanced magnetron from a graphite target with Cu fixing ring in argon under different deposition conditions. Relationships between the structure, mechanical properties, macrostress σ and coefficient of friction (CoF) μ of a-C/Cu films sputtered on Si substrates were investigated in detail. Besides, a special attention was concentrated on investigation of the effect of a deposition rate a_D of the a-C/Cu film on its hardness H and macrostress σ. Four main issues were found: (1) the addition of Cu into a-C film strongly influences its structure and mechanical properties, i.e. the hardness H, effective Young's modulus E⁎ macrostress σ and CoF, and makes it possible to form electrically conductive films; here E⁎ =  E / (1 − ν²), E is the Young's modulus, and ν is the Poisson's ratio, (2) the hardness H and compressive macrostress σ of the a-C/Cu film decrease with increasing a_D due to decreasing of total energy E_T delivered to the film during its growth, (3) hard a-C/Cu films with low value of CoF (μ ≈ 0.1) can be sputtered at high deposition rates a_D ranging from ~ 10 to ~ 80 nm/min, and (4) CoF decreases with increasing (i) hardness H and (ii) resistance of film to plastic deformation characterized by the ratio H³/E⁎² but only in the case when compressive macrostress σ is low.     

Influence of sintering aids and excess Lithium on the conductivity of perovskite-type Li3/8Sr7/16Zr1/4Nb3/4O3 solid electrolyte

Perovskite-structured Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ solid-state Lithium-conductors were prepared by conventional solid-state reaction method. Influence of sintering aids (Al₂O₃, B₂O₃) and excess Lithium on structure and electrical properties of Li_3/8Sr_7/16Zr_1/4Nb_3/4O₃ (LSNZ) has been investigated. Their crystal structure and microstructure were characterized by X-ray diffraction analysis and scanning electron microscope, respectively. The conductivity and electronic conductivity were evaluated by AC-impedance spectra and potentiostatic polarization experiment. All sintered compounds are cubic perovskite structure. Optimal amount of excess Li₂CO₃ was chosen as 20 wt% because of the total conductivity of LSNZ-20% was as high as 1.6×10⁻⁵ S cm⁻¹ at 30 °C and 1.1×10⁻⁴ S cm⁻¹ at 100 °C, respectively. Electronic conductivity of LSNZ-20% is 2.93×10⁻⁸ S cm⁻¹, nearly 3 orders of magnitude lower than ionic conductivity. The density of solid electrolytes appears to be increased by the addition of sintering aids. The addition of B₂O₃ leads to a considerable increase of the total conductivity and the enhancement of conductivity is attributed to the decrease of grain-boundary resistance. Among these compounds, LSNZ-1 wt%B₂O₃ has lower activation energy of 0.34 eV and the highest conductivity of 1.98×10⁻⁵ S cm⁻¹ at 30 °C.     

Heterometallic sulfide cluster [Ag6Sn6S20]10 −: Solvothermal syntheses and characterizations of silver thiostannates with lanthanide complex counter cations

Novel organic hybrid silver thiostannates [Hen]₄[Ln(en)₄]₂[Ag₆Sn₆S₂₀]·3en (Ln = Er, 1; Tm, 2; Yb, 3) were prepared by the reactions of Ln₂O₃, Ag, Sn and S in ethylenediamine (en) under solvothermal conditions. Six SnS₄ tetrahedra and six AgS₃ triangles are connected into the heterometallic sulfide cluster [Ag₆Sn₆S₂₀]^10 − via edge-sharing. In the [Ag₆Sn₆S₂₀]^10 − cluster, a hexanuclear Ag₆S₆ core is enclosed by two Sn₃S₁₀ fragments. The Ag₆S₆ core is the first As–S cluster stabilized by inorganic SnS₄ ligands. In 1–3, all Ln^3 + ions are in 8-fold coordination environments that involved four bidentate en ligands, forming bicapped trigonal prisms. Compounds 1–3 show well-defined absorption edges with band gaps in the range of 2.18–2.47 eV.     

Densification,microstructural evolution and dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 microwave ceramics

Utilizing different rare-earth cations R³⁺ to the Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ compounds is one of effective route to tailor the dielectric constant, quality factor and temperature coefficient of frequency. In this study, densification, microstructural evolution, and microwave dielectric properties of Ba_6 − 3x(Sm_1 − yNd_y)_8 + 2xTi₁₈O₅₄ compound, with x ranging from 0.3 to 0.7; and y from 0 to 1.00, were investigated. The ceramics with x = 0.7 [Ba_3.9(Sm_1 − yNd_y)_9.4Ti₁₈O₅₄] has a higher densification compared with others, due to the formation of vacancy, in the perovskite-like tetragonal cavity of the tungsten bronze-type framework structure. Differential thermal analysis and density results show that the densification of Ba_6 − 3x(Sm_yNd_1 − y)_8 + 2xTi₁₈O₅₄ ceramics during sintering is primarily resulting from the solid state sintering process. The phase homogeneity for the Ba_6 − 3x(Sm_0.5Nd_o.5)_8 + 2xTi₁₈O₅₄ system is at least extended in the range of x between 0.3 and 0.7. Combining different rare-earth cations appears not alter the single phase range in tungsten bronze-type Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ ceramics. The size of the columnar-grain in the microstructure increases with increasing the Nd/Sm ratio as well as the x value. Dielectric constant changes from 91.0 to 84.2 as the x increases from 0.3 to 0.7. Variation of the Nd/Sm ratio allows one to control the τ_f value to the nearly 0 ppm/°C.     

Synthesis and characterization of S2O82 −/ZnFexAl2 − xO4 solid acid catalysts for the esterification of acetic acid with n-butanol

New spinel-types of S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts were prepared by sol–gel method. Their catalytic performances for the synthesis of n-butyl acetate were investigated. The catalysts were characterized by means of XRD, IR, XPS, FT-IR of adsorbed pyridine and NH₃-TPD. The experimental results showed that S₂O₈^2 −/ZnFe_xAl_2 − xO₄ solid acid catalysts maintained the spinel structure as well as the support of ZnFe_xAl_2 − xO₄. Fe^3 + ions were well incorporated and highly dispersed into the spinel lattice. S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ exhibited the maximum conversion of acetic acid with 98.2%. Moreover, S₂O₈^2 −/ZnFe_0.15Al_1.85O₄ showed better reusability, which remained above 72.7% conversion of acetic acid even after being used five times.     

Synthesis,crystal structure and magnetic properties of a new cyanide-bridged mixed-valence copper(I)/copper(II) clathrate

A unique cyanide-bridge mixed-valence Cu^I/Cu^II clathrate of formula [Cu^I₂(CN)₃][{Cu^II(tren)}₂(μ-CN)](CF₃SO₃)₂ [tren = tris(2-aminoethyl)amine] containing cyanide-bridged [{Cu^II(tren)}₂(μ-CN)]^3 + binuclear cations stacked between anionic honeycomb layered copper(I) cyanide networks, was synthesized and structurally characterized by single crystal X-ray diffraction. Variable-temperature magnetic susceptibility studies showed that the cyanide bridge mediates a strong antiferromagnetic interaction between the copper(II) centers (J = − 160 cm^− 1, the spin Hamiltonian being defined as H = −J S_A⋅S_B).     

A novel polyoxometalate-based metal-organic compound constructed from an unprecedented [Ag8(Hpyttz)4(H2pyttz)2] cluster and an in-situ [VW12O40]3 − anion

A novel polyoxometalate (POM)-based metal-organic compound constructed from a multinuclear Ag^I cluster and Keggin-type [VW₁₂O₄₀]^3 − anion, [Ag₄(Hpyttz)₂(H₂pyttz)][HVW₁₂O₄₀]·3H₂O (1) (H₂pyttz = 5′-(pyridin-4-yl)-1H,2′H-3,3′-bi(1,2,4-triazole), was hydrothermally synthesized and characterized by IR spectroscopy, TG analysis, powder and single-crystal X-ray diffraction. In compound 1, [VW₁₂O₄₀]^3 − (VW₁₂) was in-situ transformed from [SiW₁₂O₄₀]^4 − anion. Eight Ag^I ions were connected by six Hpyttz/H₂pyttz ligands with three coordination modes forming an unprecedented [Ag₈(Hpyttz)₄(H₂pyttz)₂] cluster, which connected with six VW₁₂ anions to construct a 2-D double-layer (3,6)-connected network with {4³}₂{4⁶.6⁶.8³} topology. Moreover, the photocatalytic activity of 1 has been investigated.     

Oxygen ionic transport in SrFe1−yAlyO3−δ and Sr1−xCaxFe0.5Al0.5O3−δ ceramics

The oxygen permeability of mixed-conducting Sr_1−xCa_xFe_1−yAl_yO_3−δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO₂ gradient of 0.21/0.021 atm vary from 3.7×10⁻¹⁰ mol s⁻¹ cm⁻² to 1.5×10⁻⁷ mol s⁻¹ cm⁻² at 950 °C. The maximum solubility of Al³⁺ cations in the perovskite lattice of SrFe_1−yAl_yO_3−δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr_1−xCa_xFe_0.5Al_0.5O_3−δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO₃-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe_0.5Al_0.5O_2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe_0.7Al_0.3O_3−δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO₂ stability limits of Sr_1−xCa_xFe_1−yAl_yO_3−δ seem essentially independent of composition, varying between that of LaFeO_3−δ and the Fe/Fe_1−γO boundary. Thermal expansion coefficients of Sr_1−xCa_xFe_1−yAl_yO_3−δ ceramics in air are 9×10⁻⁶ K⁻¹ to 16×10⁻⁶ K⁻¹ at 100–650 °C and 12×10⁻⁶ K⁻¹ to 24×10⁻⁶ K⁻¹ at 650–950 °C. Doping of SrFe_1−yAl_yO_3−δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations.     

A new supramolecular assembly composed of decatungstate polyanion and Cu/O/W heterometallic cluster

A new supramolecular assembly of [(CuL)₂(WO₄)₂{CuL(H₂O)}₂][W₁₀O₃₂] · 8H₂O (1) (L = 4′-(2-pyridyl)-2,2′:6′,2′-terpyridine) containing a decatungstate polyanion and a novel cationic Cu/O/W heterometallic cluster was successfully synthesized and characterized by single crystal X-ray diffraction and IR. The tungsten atoms adopt different coordination geometry in anion and cation, octahedral geometry (WO₆) in decatungstate cluster and rare tetrahedral geometry (WO₄) in cation cluster. During the hydrothermal process, the decomposition and reassembly based on [W₆O₁₉]^2 − lead to the formation of [W₁₀O₃₂]^4 − and Cu/O/W heterometallic cluster.     

Synthesis and characterization of decanuclear Ln(III) cluster of mixed calix[8]arene-phosphonate ligands (Ln = Pr,Nd)

Two novel decanuclear Ln(III) compounds (Ln = Pr for 1, Nd for 2) have been solvothermally obtained by using p-tert-butylcalix[8]arene (H₈TBC8A) and phenylphosphonate (PhPO₃H₂) as ligands. Single crystal X-ray diffraction studies reveal that both compounds are stacked by dumbbell-like Ln₁₀ clusters, which are capped by two TBC8A^8 − supports and linked by four complementary PhPO₃^2 − ligands as well as other bridging anions. In addition, the self-assembly behavior of both compounds is interesting: the cationic Ln₁₀ cluster layers are separated by the layers of H₆TBC8A^2 − ligands. Moreover, the luminescent and magnetic properties of both compounds were examined.     

Organic–inorganic hybrid oxides: Structure and magnetic properties of [{Cu(terpy)}2Mo6O17(H2O)(O3PCH2NH2CH2PO3)2] · H2O,a bimetallic oxide constructed from novel {Mo6O17(H2O)(O3PCH2NH2CH2PO3)2}4− clusters

The hydrothermal reaction of MoO₃, CuSO₄ · 5H₂O, 2,2′:6′:2″-terpyridine (terpy) and bis-N,N-(methylphosphonic acid) amine (H₂O₃PCH₂NHCH₂PO₃H₂) provided blue crystals of the bimetallic oxide [{Cu(terpy)}₂Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂] · H₂O (1 · H₂O). The three-dimensional structure of 1 is constructed from {Mo₆O₁₇(H₂O)(O₃PCH₂NH₂CH₂PO₃)₂}⁴⁻ clusters linked through {Cu(terpy)}²⁺ subunits. The cluster consists of three pairs of edge-sharing {MoO₆} octahedra linked through corner-sharing interactions into a {Mo₆O₆} ring. One phosphonate ligand spans the diameter of the ring, bridging four molybdenum sites and leaving at a pendant {PO} group at each terminus. The second diphosphonate ligand exploits one {–PO₃} unit to cap the hexamolybdate ring and bridge all six molybdenum sites while the second {–PO₃} terminus bridges two molybdenum sites, leaving a pendant {PO} unit. Crystal data: C₃₄H₄₅Cu₂Mo₆N₈O₃₅P₄: monoclinic, P2₁/n, a = 11.9431(7) Å, b = 17.382(1) Å, c = 27.524(2) Å, β = 90.429(1)°, V = 5713.7(6) Å³, Z = 4, D_calc = 2.270 g cm⁻³, R₁ = 0.0466.     

A three-dimensional zincic molybdenum (V) phosphate with helical channel: Synthesis,structure, and electrochemical properties

A new reduced zincic molybdophosphate, (H₂bpp)₃[Zn₃Mo₁₂^VO₂₄(OH)₆(H₂O)₂(HPO₄)₆(PO₄)₂]·2H₂O 1 (bpp = 1,3-bis(4-pyridyl)propane) has been hydrothermally synthesized and characterized by elemental analysis, IR, TG, and single-crystal X-ray diffraction. Compound 1 crystallizes in the tetragonal space group I 41/a c d with a = 31.8033(4) Å, b = 31.8033(4) Å, c = 34.5593(8) Å, V = 34955.0(10) ų, and Z = 16 and exhibits a 4,6-connected 3-D framework with (3².8⁴)(3⁴.4².8³.9⁵.10) topology. The basic building blocks of [Zn(2)(Mo₆P₄)₂] are linked through [Zn(3)O₆] octahedra and [Zn(1)O₄] tetrahedra to construct 1-D chains along four different directions. Such 1-D chains are further connected by [Zn(1)O₄]²⁺ linkers to form a 3-D intricate framework with helical channels occupied by protonated bpp and water molecules. Additionally, the electrochemical property of the 1-CPE has been studied in detail.     

Co9S8–carbon composite as anode materials with improved Na-storage performance

The synthesis and electrochemical performance of a composite of Co₉S₈ nanoparticles and amorphous carbon is studied as an anode material for sodium-ion batteries. The Co₉S₈–carbon composite powder was fabricated through a one-pot spray pyrolysis process using thiourea and polyvinylpyrrolidone as sulfur and carbon sources, respectively. The Co₉S₈ nanoparticles are entirely covered by an amorphous carbon layer. The initial discharge and charge capacities of the Co₉S₈–carbon composite powder were 689 and 475 mA h g⁻¹, respectively, at a current density of 0.5 A g⁻¹. The Co₉S₈–carbon composite powders exhibited a stable cyclability with a reversible capacity of 404 mA h g⁻¹ for the 50th cycle and a superior rate capability compared with bare Co_1−xS powder. The improvement of Na-storage performance could be attributed to the small size and entanglement of the Co₉S₈ nanoparticles within the carbon matrix.