Cassiterite SnO2 Research Articles

Structural, Optical, and Magnetic Properties of Co-doped SnO2 Powders Synthesized by the Coprecipitation Technique

We have used the coprecipitation technique to synthesize polycrystalline Co-doped SnO2 diluted magnetic semiconductors with Co concentrations of 0, 0.5, and 2.0%. X-ray diffraction patterns showed for all samples the expected SnO2 tetragonal structure with no additional peaks corresponding to parasitic phases. Transmission electron microscopy (TEM) did not indicate the presence of magnetic parasitic phases and confirmed that Co ions are uniformly distributed inside the samples. Optical absorption measurements showed an energy band gap which decreases when increasing the Co concentration. Raman spectroscopy shows an intensity loss of classical cassiterite SnO2 vibration lines, which is an indication of significant structural modifications and disorder of the SnO2 lattice. Magnetization measurements revealed a mixture of paramagnetic and antiferromagnetic behavior for Co-doped SnO2 with no sign of ferromagnetism.

Preparation of tungsten oxide–tin oxide nanocomposites and their ethylene sensing characteristics

A novel method for preparation of WO 3–SnO 2 nanocomposite was described. 0.3–10.0 wt.% WO 3 was incorporated into the SnO 2 powder by precipitation of hydrated WO 3 from ammonium tungstate precursor solution containing SnO 2 powder. This preparation method resulted to uniform mixing of ∼35 nm WO 3 and ∼100 nm SnO 2 nanoparticles as revealed by direct observation using a transmission electron microscope, and by performing elemental dot mapping. Upon calcination to 500 °C, both cassiterite SnO 2 and monoclinic WO 3 were stable, and no other crystalline phase was observed. To evaluate gas sensing performance, the powders were formed into thick-film sensors using a screen printing technique. It was found that the gas sensitivity of the SnO 2 base was enhanced when very small amount of the WO 3 (0.3 wt.%) was incorporated. The 0.3 wt.% WO 3–SnO 2 sensor was very sensitive to 2–8 ppm ethylene at optimum operating temperature of 300 °C. The sensitivity decreased with increasing amount of the WO 3.

Work function of sol–gel indium tin oxide (ITO) films on glass

Indium tin oxide (ITO) films (physical thickness, 250–560±25nm) were deposited on soda lime silica (SLS) glass and silica layer coated (∼200nm physical thickness) SLS glass substrates by sol–gel technique using alcohol based precursors containing different In:Sn atomic percentages, namely, 90:10, 70:30, 50:50, 30:70. Cubic phase of In2O3 was observed up to 50at.% Sn while cassiterite SnO2 phase was observed for 70at.% Sn. Work function of the films was evaluated from inelastic secondary electron cutoff of ultraviolet photoelectron spectroscopy (UPS) energy distribution curve (EDC) obtained under two experimental conditions (i) as-introduced (ii) after the cleaning of the surface by sputtering. Elemental distribution and the presence of oxygen containing contaminant and carbon contaminant of the samples were done by XPS analysis under same conditions. The work function changed little due to the presence of surface contaminants. It was in the range, 3.9–4.2eV (±0.1eV).

Derivation of Force Field Parameters for SnO2−H2O Surface Systems from Plane-Wave Density Functional Theory Calculations

Plane-wave density functional theory (DFT-PW) calculations were performed on bulk SnO2 (cassiterite) and the (100), (110), (001), and (101) surfaces with and without H2O present. A classical interatomic force field has been developed to describe bulk SnO2 and SnO2-H2O surface interactions. Periodic density functional theory calculations using the program VASP (Kresse et al., 1996) and molecular cluster calculations using Gaussian 03 (Frisch et al., 2003) were used to derive the parametrization of the force field. The program GULP (Gale, 1997) was used to optimize parameters to reproduce experimental and ab initio results. The experimental crystal structure and elastic constants of SnO2 are reproduced reasonably well with the force field. Furthermore, surface atom relaxations and structures of adsorbed H2O molecules agree well between the ab initio and force field predictions. H2O addition above that required to form a monolayer results in consistent structures between the DFT-PW and classical force field results as well.

Preparation of oxide hollow spheres by colloidal carbon spheres

Amorphous SiO2, anatase TiO2 and cassiterite SnO2 hollow spheres have been successfully prepared using hydrophilic colloidal carbon spheres as template in conjunction with the sol–gel method. The hollow spherical structures could be confirmed by TEM and SEM. The void sizes of these hollow spheres were about 60% smaller than the diameters of the template. The BET surface areas of hollow spheres were about 183.8, 32.5, and 74.3 m2/g, respectively.

Crystal phase analysis of SnO2-based varistor ceramic using the Rietveld method

A second addition of l mol% of CoO to a pre calcined SnO2-based ceramic doped with 1.0 mol% of CoO, 0.05 mol% of Nb2O5 and 0.05 mol% of Cr2O3 promotes the appearance of a secondary phase, Co2SnO4, besides the SnO2 cassiterite phase, when the ceramic was sintered at 1350 °C/2 h. This was observed using X-ray powder diffraction, scanning electron microscopy and energy dispersive X-ray techniques. Rietveld refinement was carried out to quantify the phases present in the ceramic system. The results of the quantitative analysis were 97 wt.% SnO2 and 3 wt.% Co2SnO4. The microstructural analysis showed that a certain amount of cobalt ion remains into cassiterite grains.

High-pressure phases inSnO2to 117 GPa

X-ray diffraction of SnO2 cassiterite at high pressures and temperatures demonstrates the existence of four phase transitions to 117 GPa. The observed sequence of phases for SnO2 is rutile-type P42 /mnm → CaCl2-typePnnm → pyrite-typePa3 → ZrO2 orthorhombic phase I Pbca → cotunnite-type Pnam. Our observations of the first three phases are generally in agreement with earlier studies. The orthorhombic phase I and cotunnite-type structure orthorhombic phase II were observed in SnO2 for the first time. The Pbca phase is found at 50–74 GPa during room-temperature compression. The cotunnite-type structure was synthesized when SnO2 was compressed to 74 GPa and heated at 1200 K. The cotunnite-type form was observed during compression between 54–117 GPa with additional laser heating carried out at 91 and 111 GPa. Fitting the pressure-volume data for the high-pressure phases to the second-order Birch-Murnaghan equation of state yields a bulk modulus of 25926 GPa for the Pbca phase and 4177 GPa for the cotunnite-type phase.

Microwave heated polyol synthesis of carbon-supported PtSn nanoparticles for methanol electrooxidation

PtSn nanoparticles supported on Vulcan XC-72 carbon were prepared by a microwave-assisted polyol process. The catalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The PtSn nanoparticles, which were uniformly dispersed on carbon, were 2–7 nm in diameter. All Pt/C and PtSn/C catalysts (except Pt 35Sn 65/C) displayed the characteristic diffraction peaks of a Pt face-centered cubic (fcc) crystal structure, whereas the Pt 35Sn 65/C catalyst showed the X-ray diffraction pattern of Pt face-centered cubic (fcc) and cassiterite SnO 2 phases. XPS analysis revealed that the catalysts contained mostly Pt(0) and Sn(IV), with traces of Pt(II), Pt(IV) and Sn(0). The electro-oxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results showed that the alloy catalyst was catalytically more active and durable electrocatalytic activities for methanol oxidation than a comparative Pt/C catalyst. Preliminary data from a direct methanol fuel cell using the Vulcan carbon-supported PtSn alloy as anode catalyst showed high power density.

Production of amorphous tin oxide thin films and microstructural transformation induced by heat treatment

X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high resolution transmission electron microscopy were used to study tin oxide thin films deposited on Si(100) substrates at room temperature using pulsed laser deposition techniques with a sintered cassiterite SnO2 target and subsequently heat-treated. X-ray diffraction and scanning electron microscopy results demonstrated that the as-prepared thin films consisted of an amorphous matrix as well as plume-like features, which are shown many micropores. The thin films that were heat treated for 2 h at 150 °C had tetragonal rutile nanocrystalline SnO2 structures. The microstructural evolution of the tin oxide thin films during the heat treatment is discussed in the paper.

Structural and Dielectric Properties of MgTi2−xSnxO5

MgTi2 − xSnxO5 has been synthesized from MgO (Periclase), TiO2 (Anatase) and SnO2 (Cassiterite) by ceramic conventional mixed oxide route. The presence of tin shows superlattice lines corresponding to (030) and (221) planes in addition to karrooite phase. Both the FTIR spectral analysis and X-ray intensity analysis indicate that the structural properties optimize at x = 0.2. The dielectric constant (K′) and the relative dielectric loss (K″) as well as tan δ have been measured as a function of frequency as well as temperature. The dielectric hysteresis loop is attributed to order-disorder transition. On the basis of these observations it is concluded that small value of dielectric constant is attributed to 1) migrational polarization and 2) cation disorder. Following the researcher's interest in dependence of cation disorder in MgTi2O5 on pressure, the variation of dielectric constant as a function of pressure has been measured. On the basis of these measurements, it is concluded that these materials may prove to be potential pressure sensors.

Nucleation mechanism and microstructural assessment of SnO 2 nanowires prepared by pulsed laser deposition

Tin dioxide, SnO 2, nanowires have been successfully synthesized by a pulsed laser deposition process based on a sintered cassiterite SnO 2 target, being deposited on Si (100) substrates at room temperature. Transmission electron microscopy shows that nanowires are structurally perfect and uniform, and diameters range from 10 nm to 30 nm, and lengths of several hundreds nanometers to a few micrometers. X-ray diffraction and energy dispersive X-ray spectroscopy analysis indicate that the nanowires have the same crystal structure and chemical composition found in the tetragonal rutile form of SnO 2. Selected area electron diffraction and high-resolution transmission electron microscopy reveal that the nanowires grow along the [110] growth direction. In addition to the fundamental Raman scattering peaks, the other two Raman scattering peaks are also observed. We discussed the possible reasons for the appearance of Raman scattering peaks at 518.7 and 701.8 cm −1. The growth process of the SnO 2 nanowires is suggested to follow a vapor–solid mechanism.

EXAFS and XANES study of two novel Pd doped Sn/SnOx nanomaterials

EXAFS and XANES at the Pd and Sn K-edges have been used to characterise a novel palladium doped Sn/SnOx nanocomposite that have found application in a new type of high performance solid-state gas sensor. The spherical nanoparticles (10 to 65 nm diameter) prepared either by co-decomposition of Sn and Pd organometallic precursors (doping in volume) or by decomposition of a palladium precursor on preformed Sn/SnOx coreshell nanoparticles (doping in surface) consist of a tin metallic core surrounded by some small platelets of a well-crystallised material embedded in an outer layer of amorphous tin oxide. In this layer tin atoms in an oxidation state close to +IV, are four-fold coordinated to oxygen with bond distances slightly larger than in bulk cassiterite SnO2. In both samples palladium was found to be always in a metallic state, only surrounded by Sn and Pd atoms located at unusually short distances. The two samples that differ mainly by their Pd coordination number present very different morphologies and electrical properties when fully oxidised. A possible location of the Pd atoms in these two materials is proposed.

Combustion Synthesis and Characterization of Nanocrystalline Tin and Tin Oxide (SnOx, x= 0–2) Particles

Nanocrystalline SnOx particles (x= 0–2) were synthesized using tetramethyltin (Sn(CH3)4) vapor as the particle precursor reactant in hydrogen/oxygen/argon (H2/O2/Ar) flames. The particle composition and morphology were characterized using X‐ray diffractometry, transmission electron microscopy, and nitrogen (N2) surface adsorption. By controlling the concentration of oxygen in the reactant gases and the flame temperatures, metallic tin (Sn), tin monoxide (romarchite SnO), and/or tin dioxide (cassiterite SnO2) were generated. The crystalline powders consisted of both discrete primary particles and agglomerates, with average primary particle sizes of 23–24 nm for SnO2 and 69 nm for Sn (based on specific surface area measurements of bulk powders collected in the exhaust region of the flame). The compositional results were interpreted using equilibrium and detailed chemical kinetics models.

EXAFS and XANES Study of a Pure and Pd Doped Novel Sn/SnOx Nanomaterial

EXAFS and XANES at the Pd and/or Sn K-edge have been used to characterize pure and palladium doped spherical particles (10−63 nm diameter) of a novel Sn/SnOx nanocomposite. This nanomaterial prepared by decomposition of organic precursors has found application in a new type of high performance solid-state gas sensor. Except for the sample annealed at 600 °C that is mainly pure crystalline tetragonal cassiterite SnO2, the undoped nanoparticles consist of a Sn metallic core surrounded by a layer of tin oxide that is mostly amorphous. In this outer layer, tin atoms were found to be 4−5-fold coordinated to oxygen with bond distances slightly larger than in bulk cassiterite SnO2. The average tin oxidation state in the oxide phase was evaluated using the length of the tin−oxygen bond to be between +3.7 and +3.5. The relative ratio of Sn atoms in the metallic phase was estimated between 15 and 36% of the total number of Sn atoms using the coordination number of the first Sn shell corresponding to the tin β tetra...

Fe2O3:SnO2 Nanostructured System as Semiconductor Gas Sensor Material

ABSTRACTIn the present work, we report a detailed study based on transmission electron microscopy of the microstructure and composition of the Fe2O3: SnO2 nanometrical binary system obtained by sol-gel. We studied a set of samples based in a pure Fe2O3 material where we added SnO 2 from 0 to 50% Sn-Fe nominal content. The structure of our composites will change from pure a-Fe2O3 to the well-known cassiterite SnO 2 structure for high Sn content. Distortions on the structural parameters will be attributed to the presence Sn4+ ions on the α-Fe2O3 structure and Fe3+ ions on the SnO2 cassiterite structure.

Development of Sol-Gel Fluorine Doped Tin Oxide Film on Glass

Conductive and transparent thin films of F-doped SnO2 were deposited on soda lime silica glass by utilizing the sol-gel dipping technique. The chosen composition of Sn: F in the precursor sol was in the range 99: 1 to 97: 3 (atomic ratio). The developed films (thickness 0.1—0.8 μm; refractive index 1.6–2.0) were of cassiterite SnO2 phase. Resistivity of the films was V-type with increase of F content and passed through a minimum at Sn: F = 97.5: 2.5. Visible transmission (89%-50%) of the films was dependent on film thickness and its refractive index. Microstructure of the films indicated porous surface feature.

Microstructural and morphological analysis of pure and Ce-doped tin dioxide nanoparticles

Structural and morphological studies in pure and Ce-doped tin dioxide nanoparticles with high stability against particle growth were performed in samples, obtained using the polymeric precursor method and prepared at different annealing temperatures. A Ce-rich surface layer was used to control the particle size and stabilize SnO 2 against particle growth. The formation of this segregated layer can contribute to a decreased surface energy, acting in the driving force, or reducing the surface mobility. Only the cassiterite SnO 2 phase was observed below 1000 °C and a secondary phase (CeO 2 ) was observed for the Ce-doped SnO 2 at temperatures higher than 1000 °C, when de-mixing process occurs. The evolution of crystallite size, microstrain and morphology of the nanoparticles with annealing temperatures was investigated by X-ray diffraction (XRD), associated to Rietveld refinements, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Synthesis and characterization of crystalline tin oxide nanoparticles

Monodisperse non-aggregated spheroidal nanoparticles of SnO2 cassiterite are prepared through hydrolysis of tin isopropoxide in the presence of acetylacetone and p-toluenesulfonic acid, followed by ageing at 60 °C. The obtained sols remain stable for several months at 4 °C. The nanoparticles have been characterized in the solid state (xerosol) by powder X-ray diffraction, TEM, FTIR, TGA-DTA, and 119Sn MAS and 13C CP-MAS NMR. The mean size of the cassiterite oxide core is about 1–2 nm. These particles do not aggregate in suspension because their surfaces are protected by an hybrid organic–inorganic layer containing acetylacetonate ligands, acetylacetone, p-toluenesulfonates and water.

Fabrication and Structural Characterization of Large-Scale Uniform SnO2 Nanowire Array Embedded in Anodic Alumina Membrane

Semiconductor SnO2 nanowire arrays were fabricated by electrochemical deposition and thermal oxidizing methods based on highly ordered nanoporous alumina membrane. Their microstructures were characterized by X-ray diffraction, transmission electron microscopy, Raman spectrum, and scanning electron microscopy. The results indicate that the SnO2 nanowire array with cassiterite polycrystalline structure is uniformly assembled into the hexagonally ordered nanochannels of anodic alumina membranes. There are three phases (Sn, SnO, and SnO2) coexisting when the as-deposited assembly system is annealed at 823 K. However, only the SnO2 cassiterite phase is detected when the assembly system is annealed at 923 K.

Synthesis, open-framework structure and thermal behaviour of ammonium tin oxalate, Sn2(NH4)2(C2O4)3·3H2O

A new mixed ammonium tin oxalate trihydrate, Sn2(NH4)2(C2O4)3·3H2O, has been prepared from evaporation of a solution of tin and ammonium oxalates. Its crystal structure has been solved from single-crystal diffraction data. The symmetry is orthorhombic, space group Pnma (No. 62), cell dimensions a=15.1821(5) Å, b=11.7506(2) Å, c=10.8342(3) Å, and Z=4. The structure consists of macroanionic layers built from [Sn(C2O4)3]2– groups. The SnO6 polyhedron can be described as a pseudo pentagonal bipyramid, with the lone pair of electrons presumably occupying one apex. The resulting framework displays holes in which the water molecules and ammonium groups are located. The thermal behaviour of the mixed ammonium tin oxalate has been investigated with temperature-dependent X-ray powder diffraction and conventional thermal analysis. The degradation process has been completely explained, as well as that of oxammite, a phase always obtained in the preparations. The thermal decomposition of oxammite leads to (NH4)2C2O4 and a new acid salt, NH4HC2O4. The mixed ammonium tin oxalate decomposes successively into the amorphous compounds, Sn2(NH4)2(C2O4)3·H2O and Sn2(NH4)2(C2O4)3, SnC2O4 and, finally, cassiterite SnO2.