Electrical and magnetic properties of semimetallic and semiconducting alloys of BiSb

Studies on electrical conductivity, thermoelectric power (t.e.p), Hall effect and diamagnetic susceptibility have been carried out on two inhomogeneous Bi-Sb alloys in the temperature range 100–300 K. Measurements have been confined to the plane perpendicular to the three-fold axis. Antimony impurity levels have been postulated to exist between the bands L_v and L_c. These levels together with the existing band structure of Bi-Sb alloys can explain the observed behaviour of both the alloys of which one is a semimetal and the other a semiconductor. The semiconductor-metal transitions induced by magnetic fields as observed earlier, could also be explained with the help of these antimony levels. The majority of the carriers in both the cases are holes. The different electronic parameters including density of carriers, mobility, nature of the charge carriers and effective masses for all the three bands have been calculated.     

Alpha and beta isomers of tetrahafnium(IV) containing decatungstosilicates, [Hf4(OH)6(CH3COO)2(x-SiW10O37)2]12- (x = α, β)

The two dimeric, Hf-containing tungstosilicates [Hf(4)(OH)(6)(CH(3)COO)(2)(α-SiW(10)O(37))(2)](12-) (1) and [Hf(4)(OH)(6)(CH(3)COO)(2)(β-SiW(10)O(37))(2)](12-) (2) have been synthesized by reacting HfCl(4) with [γ-SiW(10)O(36)](8-) in potassium acetate solutions at pH = 3.6 and 4.8, respectively. Polyanions 1 and 2 comprise a tetrahafnium(iv) assembly {Hf(4)(OH)(6)(CH(3)COO)(2)} sandwiched between two dilacunary [α-SiW(10)O(36)](8-) (in 1) or {β-SiW(10)} (in 2) Keggin type decatungstosilicates. This implies that the starting precursor {γ-SiW(10)} isomerizes in situ to [β-SiW(10)O(37)](10-) and then to [α-SiW(10)O(37)](10-) by controlled variation of pH and temperature. The hydrated potassium salts of 1 and 2 were investigated in the solid state by single-crystal XRD, FT-IR, thermogravimetric and elemental analyses, and in solution by UV-Vis and (183)W NMR spectroscopy, and electrochemistry.     

Crystal structures and thermoelectric properties of the series Tl(10-x)La(x)Te6 with 0.2 ≤ x ≤ 1.15

The tellurides Tl(10-x)La(x)Te(6) were synthesized from the elements in stoichiometric ratios at 873 K, followed by slow cooling. These materials are substitution variants of Tl(5)Te(3), crystallizing in space group I4/mcm, with lattice dimensions of a = 8.9220(4) ?, c = 13.156(1) ?, V = 1047.2(1) ?(3), for x = 1 (Z = 2). Increasing the La content occurs with an increase in the unit cell volume and the c axis, but a decrease of the a axis. Tl(5)Te(3) is a metallic compound, while Tl(9)LaTe(6) was calculated to be semiconducting. Correspondingly, the Seebeck coefficient increases with increasing x, while the electrical and thermal conductivity both decrease. The highest thermoelectric figure-of-merit determined thus far is 0.21 at 581 K for cold-pressed Tl(9)LaTe(6).     

Effect of magnetic field on the buoyancy and thermocapillary driven convection of an electrically conducting fluid in an annular enclosure

The main objective of this article is to study the effect of magnetic field on the combined buoyancy and surface tension driven convection in a cylindrical annular enclosure. In this study, the top surface of the annulus is assumed to be free, and the bottom wall is insulated, whereas the inner and the outer cylindrical walls are kept at hot and cold temperatures respectively. The governing equations of the flow system are numerically solved using an implicit finite difference technique. The numerical results for various governing parameters of the problem are discussed in terms of the streamlines, isotherms, Nusselt number and velocity profiles in the annuli. Our results reveal that, in tall cavities, the axial magnetic field suppresses the surface tension flow more effectively than the radial magnetic field, whereas, the radial magnetic field is found to be better for suppressing the buoyancy driven flow compared to axial magnetic field. However, the axial magnetic field is found to be effective in suppressing both the flows in shallow cavities. From the results, we also found that the surface tension effect is predominant in shallow cavities compared to the square and tall annulus. Further, the heat transfer rate increases with radii ratio, but decreases with the Hartmann number.     

Yttrium(III)-containing tungstoantimonate(III) stabilized by tetrahedral WO4(2-) capping unit, [{Y(α-SbW9O31(OH)2)(CH3COO)(H2O)}3(WO4)]17-

The yttrium(III)-containing tungstoantimonate(III) [{Y(α-SbW(9)O(31)(OH)(2))(CH(3)COO)(H(2)O)}(3)(WO(4))](17-) (1) has been synthesized in a simple one-pot reaction of Y(3+) ions with [α-SbW(9)O(33)](9-) and WO(4)(2-) in a 3:3:1 molar ratio in 1 M LiOAc/AcOH buffer at pH 5.3. Polyanion 1 is composed of three (α-SbW(9)O(33)) units linked by three Y(3+) ions and a capping, tetrahedral WO(4)(2-) capping unit, resulting in an assembly with C(3v) symmetry. The hydrated ammonium-sodium salt of 1 was investigated in the solid state by single-crystal XRD, FT-IR spectroscopy, thermogravimetric and elemental analyses, and in solution by multinuclear NMR spectroscopy.     

The chemistry of cadmium-thiocarboxylate derivatives: synthesis, structural features, and application as single source precursors for ternary sulfides

Novel heterobimetallic complexes [(PPh(3))(2)Cu(μ-SCOPh)(2)Cd(SCOPh)] (2a), [(PPh(3))(2)Cu(μ-SCOth)(2)Cd(SCOth)] (2b), [(PPh(3))(2)Ag(μ-SCOth)(2)Cd(SCOth)] (3a), [(PPh(3))(2)Ag(μ-SCOth)(2)Cd(H(2)O)(SCOth)] (3b), [(PPh(3))(2)Ag(μ-SCOPh)(2)Cd(SCOPh)] (3c), and a bimetallic complex [PPh(3)Cd(μ-SCOth)SCOth](2)·CH(2)Cl(2) (5) (th = thiophene) were prepared and characterized by single crystal X-ray diffraction analysis. A coordination polymer [Cd(SCOPh)(2)](n) (4) has also been characterized structurally that exhibited metal-like electrical conductivity. The heterobimetallic complexes on pyrolyzing under controlled conditions yielded ternary sulfides of composition CuCd(7)S(8), CuCd(10)S(11), Ag(2)Cd(8)S(9), and Ag(2)Cd(5)S(6), which have been characterized by SEM-EDX and X-ray diffractometry. Photophysical properties and electrical conductivities of the sulfides have also been studied.     

Absorption Spectrophotometric,NMR and Quantum Chemical Investigations of Ground State Non-Covalent Interactions between Fullerenes and a Designed Trihomocalix[6]arene in Solution

Ground state non-covalent interactions between a newly designed macrocyclic 1,3,5-trihomo calix[6]arene receptor, designated as 1, and the C₆₀ and C₇₀ fullerenes have been studied in toluene solutions. It was observed that the absorbances of both C₆₀ and C₇₀ solutions increased upon the addition of increasing concentrations of compound 1. Job’s method of continuous variation established 1:1 stoichiometry for these fullerene-1 complexes. The binding constant (K) data reveal that compound 1 binds to C₇₀ more strongly compared to C₆₀, i.e., K_C60-1 = 230 dm³·mol^-1K_{C60\mbox{-}\boldsymbol{1}} = 230~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1} and K_C70-1 = 517 dm³·mol^-1K_{C70\mbox{-}\boldsymbol{1}}= 517~\mathrm{dm}^{3}{\cdot}\mathrm{mol}^{-1}. Proton NMR analysis provides very good support for strong binding between C₇₀ and 1. Estimations of the solvent reorganization energy (R _S ) suggest that the C₇₀-1 complex is stabilized more than the corresponding C₆₀-1 complex, with R_S(C60-1) = -1.970 eVR_{S(C60\mbox{-}\boldsymbol{1})} = -1.970~\mathrm{eV} and R_S(C70-1) = -2.300 eVR_{S(C70\mbox{-}\boldsymbol{1})}= -2.300~\mathrm{eV}. Molecular mechanics force field method calculations established that the binding pattern of C₇₀ towards 1 occurs in the side-on rather than end-on orientation, and that the C₇₀-1 complex gains 5.23 kJ⋅mol⁻¹ of extra stabilization energy with this side-on geometrical arrangement.     

Naked-eye detection of F and AcO ions by Schiff base receptor

A Schiff base 2, composed with o-phenylenediamine and 5-nitro-salicylaldehyde have been synthesized as an anion receptor. It consists with conjugated imine, phenolic -OH and electron withdrawing substituent nitro (-NO₂) group. Receptor 2 can recognize selectively biologically important F⁻ and AcO⁻ ions. The recognition properties have been investigated by naked-eye color change (colorless to yellow), followed by UV-vis spectral changes. Predicted stoichiometries of the complexes between receptor 2 and anions based on density functional theory (DFT) level calculations, corroborates well with experimental findings.     

New barium copper chalcogenides synthesized using two different chalcogen atoms: Ba2Cu(6-x)STe4 and Ba2Cu(6-x)Se(y)Te(5-y)

Ba(2)Cu(6-x)STe(4) and Ba(2)Cu(6-x)Se(y)Te(5-y) were prepared from the elements in stoichiometric ratios at 1123 K, followed by slow cooling. These chalcogenides are isostructural, adopting the space group Pbam (Z = 2), with lattice dimensions of a = 9.6560(6) ?, b = 14.0533(9) ?, c = 4.3524(3) ?, and V = 590.61(7) ?(3) in the case of Ba(2)Cu(5.53(3))STe(4). A significant phase width was observed in the case of Ba(2)Cu(6-x)Se(y)Te(5-y) with at least 0.17(3) ≤ x ≤ 0.57(4) and 0.48(1) ≤ y ≤ 1.92(4). The presence of either S or Se in addition to Te appears to be required for the formation of these materials. In the structure of Ba(2)Cu(6-x)STe(4), Cu-Te chains running along the c axis are interconnected via bridging S atoms to infinite layers parallel to the a,c plane. These layers alternate with the Ba atoms along the b axis. All Cu sites exhibit deficiencies of up to 26%. Depending on y in Ba(2)Cu(6-x)Se(y)Te(5-y), the bridging atom is either a Se atom or a Se/Te mixture when y ≤ 1, and the Te atoms of the Cu-Te chains are partially replaced by Se when y > 1. All atoms are in their most common oxidation states: Ba(2+), Cu(+), S(2-), Se(2-), and Te(2-). Without Cu deficiencies, these chalcogenides were computed to be small gap semiconductors; the Cu deficiencies lead to p-doped semiconducting properties, as experimentally observed on selected samples.