An ab-initio study of the role of lone pairs in the structure and insulator-metal transition in SnO and PbO

We have performed density functional calculations on tetragonal SnO and PbO (litharge) in the space group P4/nmm with the specific intention of examining the role played by Sn 5s and Pb 6s lone pairs in stabilizing the structure, and in giving rise to semi-metallic behavior (of SnO at ambient pressure and of PbO in the gamma phase). Use of the electron localization function has permitted real-space visualization of the lone pair in these structures. We also discuss the electronic structure of the orthorhombic PbO (massicot, space group Pbma) which again has localized lone pairs, contrary to some earlier expectation. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Surface oxidation of cadmium, indium, tin and antimony by photoelectron and Auger spectroscopy

Surface oxidation of Cd, In, Sn and Sb has been investigated by employing valence bands, metal 4d levels and plasmon bands in X-ray photoelectron spectra. O(KLL), metal M4N45N45, and plasmon transitions in electron-induced Auger spectra as well as Auger transitions due to the metal (metal oxide) and plasmons in X-ray-induced Auger spectra. The surface oxides are In2O4, CdO and a mixture of SnO and SnO2 in the case of In. Cd and Sn respectively. The facility of surface oxidation is found to vary as In>Cd>Sn>Sb. Inter-atomic Auger transitions involving oxygen valence bands have been identified on oxidized surfaces of Cd and In.

Electron-hole recombination in cobalt-doped p-type germanium

The recombination properties of cobalt centers in p-type germanium containing cobalt in the concentration range 1014 to 1016 atoms/cm3 have been investigated. The measurement of lifetime has been carried out by steady-state photoconductivity and photo-magneto-electric methods in the temperature range 145 to 300°K. The cross-sections Sno (electron capture cross-section at neutral centers). Sn- (electron capture cross-section at singly negatively charged centers) and their temperature variations have been estimated by the analysis of the lifetime data on the basis of Sah-Shockley's multi-level formula. The value of Sno is (15±5).10-16 cm2 and is temperature independent. The value of Sn- is ≈4·10-16 cm2 around 225°K and it increases with increase of temperature. The possible mechanisms for capture at neutral and repulsive centers are discussed and a summary of the capture cross-sections for cobalt centers is given. A comparison of the cross-section values of cobalt and their temperature variations with those of the related impurities-manganese, iron and nickel-in germanium has been made.

Visualizing lone pairs in compounds containing heavier congeners of the carbon and nitrogen group elements

In this mini-review, I discuss some recent work on the stereochemistry and bonding of lone pairs of electrons in divalent compounds of the heavier carbon group elements (SnII, PbII) and in trivalent compounds of the heavier nitrogen group elements (BiIII). Recently developed methods that permit the real-space visualization of bonding patterns on the basis of density functional calculations of electronic structure, reveal details of the nature of s electron lone pairs in compounds of the heavier main group elements – their stereochemistry and their inertness (or lack thereof). An examination of tetragonal P4/nmm SnO, a-PbO and BiOF, and cubic Fm3m PbS provides a segue into perovskite phases of technological significance, including ferroelectric PbTiO3 and antiferroelectric/piezoelectric PbZrO3, in both of which the lone pairs on Pb atoms play a pivotal rôle.

Thermodynamics of oxygen in liquid copper-tin alloys

The activity coefficients of oxygen in copper-tin alloys at 1 1 00°C have been measured by two different equilibrium methodsthe cell Pt, Ni + NiO I ZrOz solid electrolyte I O[Cu + Sn], cermet. Pt and the equilibrium between Cu + Sn alloys and SnO + SiO, slags established via SnO vapour. The results from both types of measurement confirm the work of Block and co-workers and show that other data are in error. The deoxidation equilibria for Sn in liquid copper, with solid SnO, as deoxidation product, have been evaluated at temperatures of interest in copper smelting.

Electrochemical Determination of the Stability of Mono- and Dicalcium Stannates

he thermodynamic properties of mono- and dicalcium stannates have been determined in the temperature range 973–-1423°K from the electromotive force measurements on solid oxide galvanic cells[dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]0[sub 3] - ThO[sub 2]//SnO[sub 2] + Sn, W, Pt][dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]O[sub 3] - ThO[sub 2]//CaSnO[sub 3] + SnO[sub 2] + Sn, W, Pt][dformula Pt, Ni + NiO//CaO - ZrO[sub 2]/Y[sub 2]O[sub 3] - ThO[sub 2]/Ca[sub 2]SnO[sub 4] + CaSnO[sub 3] + Sn, W, Pt]and [dformula Pt, Ni + NiO//CaO - ZrO[sub 2]sol;Y[sub 2]O[sub 3] - ThO[sub 2]//Ca[sub 2]SnO[sub 4] + CaO, W, Pt] The Gibbs free energy changes accompanying the formation of the stannates from component oxides may be represented by the equations[dformula 2CaO + SnO[sub 2] --> Ca[sub 2]SnO[sub 4]][dformula Delta G[degree] = - 17,040 + 0.85T ([plus-minus]300) cal][dformula CaO + SnO[sub 2] --> CaSnO[sub 3]][dformula Delta G[degree] = - 17,390 + 2.0T ([plus-minus]300) cal]The partial pressures of the tin bearing oxide species resulting from the decomposition of the stannates have been calculated as a function of the oxygen partial pressure by combining the results of this study with published information on the partial pressures and composition of oxide species over stannic oxide.

Kinetics of carbon monoxide oxidation with Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts

Base metal substituted Sn(0.95)M(0.05)O(2-delta) (M = Cu, Fe, Mn, Co) catalysts were synthesized by the solution combustion method and characterized by XRD, XPS, TEM and BET surface area analysis. The catalytic activities of these materials were investigated by performing CO oxidation. The rates and the apparent activation energies of the reaction for CO oxidation were determined for each catalyst. All the substituted catalysts showed high rates and lower activation energies for the oxidation of CO as compared to unsubstituted SnO(2). The rate was found to be much higher over copper substituted SnO(2) as compared to other studied catalysts. 100% CO conversion was obtained below 225 degrees C over this catalyst. A bifunctional reaction mechanism was developed that accounts for CO adsorption on base metal and support ions and O(2) dissociation on the oxide ion vacancy. The kinetic parameters were determined by fitting the model to the experimental data. The high rates of the CO oxidation reactions at low temperatures were rationalized by the high dissociative chemisorption of adsorbed O(2) over these catalysts.

Phase and Dimensionality of Tin Oxide at graphene nanosheet array and its Electrochemical performance as anode for Lithium Ion Battery

We incorporated tin oxide nanostructures into the graphene nanosheet matrix and observed that the phase of tin oxide varies with the morphology. The highest discharge capacity and coulumbic efficiency were obtained for SnO phase of nanoplates morphology. Platelet morphology of tin oxide shows more reversible capacity than the nanoparticle (SnO2 phase) tin oxide. The first discharge capacity obtained for SnO@GNS is 1393 and 950 mAh/g for SnO2@GNS electrode at a current density of 23 mu A/cm(2). A stable capacity of about 1022 and 715 mAh/g was achieved at a current rate of 23 mu A/cm(2) after 40 cycles for SnO@GNS and SnO2@GNS anodes, respectively. (C) 2014 Elsevier Ltd. All rights reserved.