Sol-gel preparation and characterisation of mixed metal tin oxide thin films

Mixed metal oxide stannates were prepared by sol-gel methods and coated onto solid titanium substrates as thin films using spin and dip coating methods. Metal oxides such as Sb₂O₅, ZrO₂, CuO, MnO_x and PdO were introduced into a SnO₂ host matrix using sol-gel technology. The mixed metal tin oxide materials prepared via the sol-gel route were extensively characterised in terms of surface characterisation and chemical composition. Thermogravimetric analysis was performed to confirm that at 600 °C (the calcination temperature) no further structural changes due to mass loss occur. UV spectroscopy of the liquid gels allowed the determination of the band gap energy. The surface morphology of the thin film electrodes were characterised by atomic force microscopy and scanning electron microscopy and the effect of the coating method employed i.e. spin or dip coating could be clearly seen in the estimated values of surface roughness. These techniques were also able to confirm the thickness of the films in the nano range. Combined nuclear beam techniques such as Rutherford backscattering spectroscopy and particle induced X-ray emission provided some insight into the chemical composition of the mixed metal tin oxides and confirmed the presence of the dopant element in the SnO₂ host material.     

Preparation of tin oxide monolith by the sol-gel method from inorganic salt

Tin oxide monolith was prepared by a sol-gel process using inorganic salt as a starting material. The tin oxide prepared had no aggregations visible to the naked eye and was very transparent in the visible wavelength even after heating in air at 600 °C. It was confirmed from X-ray diffraction results that the crystal structure of the tin oxide was of the rutile type. The crystal size changed from 1.4 nm to 23.5 nm as the heating temperature increased from room temperature to 700 °C, indicating a possibility to control the crystal size.     

A single target RF magnetron co-sputtered iron doped tin oxide films with pillars

The SnO₂ gas sensors and catalytic surfaces are produced by different techniques with a wide range of dopants improving their selectivity and sensitivities. The surface topology is important because the active surface area can be enlarged dramatically by employing nanostructures. Many reported techniques for the tin oxide nanostructures preparation require fine powders or liquid precursors together with high temperatures above 500 °C. But the nanostructures can be formed by the RF off-axis magnetron sputtering technique at room temperature from a bulk target. The single target co-sputtering of SnO₂ target with Fe inset was used to deposit SnO₂ film doped by iron.The 400 nm diameter pillars were successfully deposited in controllable density on polished Si substrates at low pressure 0.3 Pa of argon and oxygen gas mixture. The pillars were not formatted at the beginning of deposition process but certain SnO₂ film was required. The surface around the pillars was flat without any significant texture.The iron in form of the iron oxide was found to be the doping in deposited coatings when the stannic oxide was sub-stoichiometry with oxygen vacancies.     

The effect of Tb doping on the structure and spectroscopic properties of MgAl2O4 nanopowders

In this paper, a modified sol-gel method was employed to prepare nanostructured MgAl₂O₄ spinel powders doped with Tb³⁺ ions and thermally treated at 700 and 1000 °C for 3 h. The structural properties of the prepared at 700 and 1000 °C powders where characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). According to obtained XRD patterns the formation of single-phase spinels after calcination was confirmed. The XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The Rietveld method was applied to calculate lattice parameters. The averaged spinel particle size was determined to be ∼10 nm for calcination at 700 °C and ∼20 nm at 1000 °C. The emission and excitation spectra measured at room and low temperature (77 K) for the samples calcined at 700 and 1000 °C demonstrated characteristic spectra of Tb³⁺ ions. The effect of MgAl₂O₄:Tb³⁺ grain sizes on luminescence properties was noticed.     

Preparation of transparent conductive indium tin oxide thin films from nanocrystalline indium tin hydroxide by dip-coating method

Indium tin oxide (ITO) thin films with well-controlled layer thickness were produced by dip-coating method. The ITO was synthesized by a sol-gel technique involving the use of aqueous InCl₃, SnCl₄ and NH₃ solutions. To obtain stable sols for thin film preparation, as-prepared Sn-doped indium hydroxide was dialyzed, aged, and dispersed in ethanol. Polyvinylpyrrolidone (PVP) was applied to enhance the stability of the resulting ethanolic sols. The transparent, conductive ITO films on glass substrates were characterized by X-ray diffraction, scanning electron microscopy and UV-Vis spectroscopy. The ITO layer thickness increased linearly during the dipping cycles, which permits excellent controllability of the film thickness in the range ~ 40-1160 nm. After calcination at 550 °C, the initial indium tin hydroxide films were transformed completely to nanocrystalline ITO with cubic and rhombohedral structure. The effects of PVP on the optical, morphological and electrical properties of ITO are discussed.     

Properties of indium oxide/tin oxide multilayered films prepared by ion-beam sputtering

The preparation and characterization of indium oxide (InO _x )/tin oxide (SnO _y ) multilayered films deposited by ion-beam sputtering are described and compared with indium tin oxide (ITO) films. The structure and the optoelectrical properties of the films are studied in relation to the layered structures and the post-deposition annealing. Low-angle X-ray diffraction analysis showed that most films retained the regular layered structures even after annealing at 500° C for 16 h. As an example, we obtained a resistivity of 6×10^–4 cm and a transparency of about 85% in the visible range at a thickness of 110 nm in a multilayered film of InO _x (2.0 nm)/SnO _y (0.2 nm)×50 pairs when annealed at 300° C for 0.5 h in air. Hall coefficient measurements showed that this film had a mobility of 17 cm² V^–1 sec^–1 and a carrier concentration (electron density) of 5×10²⁰ cm^–3.     

Understanding the electrochemical behavior of Sn(II) in choline chloride-ethylene glycol deep eutectic solvent for tin powders preparation

Tin is one of the vital substances in the material and chemical industry. Deep eutectic solvent (DES) possesses excellent physicochemical properties for metal preparation. In this study, the electrochemical behavior of Sn(II) and metallic tin preparation in choline chloride-ethylene glycol (ChCl-EG) DES were investigated. Linear sweep voltammetry is carried out to study the effects of substrate material (Ni, Cu, Pt, C, Fe, Al, W, glassy carbon (GC) and Ti), temperature (313–353 K) and SnCl₂ concentration (10–100 mM) on the electrochemical behavior of Sn(II)/Sn. Results demonstrate that metallic tin is easier to be prepared on the Ni electrode, and increasing temperature and SnCl₂ concentration both facilitate the reduction of Sn(II). Electrospray ionization mass spectrometry (ESI-MS) shows that the main form of Sn(II) is [SnCl₃]^-. Chronoamperometric tests indicate that with the increase of applied potential, the nucleation of Sn(II) on the nickel electrode becomes close to the instantaneous nucleation. Simultaneously, the nucleation rate and the number of active sites on the electrode surface increase significantly. Pure tin with a dendritic structure could be prepared with higher current efficiency of 96.4% and lower energy consumption of 320.5 kW·h·t^?1 without any additives. All these studies provide a fundamental basis for the preparation of tin powders in ChCl-EG DES.     

Dye-sensitized solar cells with TiO2 nanocrystalline films prepared by conventional and rapid thermal annealing processes

Titanium oxide (TiO₂) thin films are prepared by the sol-gel method and annealed at 600 °C by conventional (CTA) and rapid thermal annealing (RTA) processes on fluorine-doped tin oxide -coated glass substrates for application as the work electrode for the dye-sensitized solar cells (DSSC). TiO₂ thin films are crystallized using a conventional furnace and the proposed RTA process at annealing rates of 5 °Cmin⁻¹ and 600 °Cmin⁻¹, respectively. The TiO₂ thin films are characterized by X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller analysis. Based on the results, the TiO₂ films crystallized by RTA show better crystallization, higher porosity and larger surface area than those of CTA. The short-circuit photocurrent and open-circuit voltage values increased from 5.2 mAcm⁻² and 0.6 V for the DSSC with the CTA-derived TiO₂ films to 8.3 mAcm⁻² and 0.68 V, respectively, for the DSSC containing RTA-derived TiO₂ films.     

Magnetic properties of nano-clusters lanthanum chromite powders doped with samarium and strontium ions synthesized via a novel combustion method

A novel approach to synthesize a single-phase orthorhombic perovskite lanthanum chromite LaCrO₃ clusters doped with Sm³⁺ and Sr²⁺ ions via gel combustion route was reported. The producing materials were synthesized using metal nitrates as oxidizers and triethanol amine (TEA), N-butyl amine (NBA) or ethylene diamine (EDA) as a fuel. The effect of the annealing temperature, type of organic fuel and the variation of the samarium and/or strontium substitution and its impact on crystal structure, crystallite size, microstructure and magnetic properties of the LaCrO₃ powders formed was systematically studied. The results revealed that a well crystalline single phase of pure LaCrO₃ can be achieved at annealing temperature from 800 to 1000 °C for 2 h. Moreover, each organic carrier materials exhibited a different degree of effectiveness in the synthesis of the mixed oxide powders. The crystal structure was influenced by doped Sm³⁺ and/or Sr²⁺ ions. The crystallite size of the produced powders was increased with the increase the annealing temperature, increasing the Sm³⁺ ion and the decrease of Sr²⁺ ion substitution. The microstructures of the produced powders were found to be nanoclusters octahedra-like shaped. The saturation magnetization of the LaCrO₃ powders increased continuously with an increase in the Sm³⁺ ion concentration and it decreased with an increase in the Sr²⁺ ion up to 0.3 at annealing temperature of 1000 °C for 2 h. The maximum saturation magnetization (0.279 emu/g) was achieved at the Sm³⁺ ion molar ratio 0.3 and annealing temperature 1000 °C. Moreover, wide coercivities can be obtained at different synthesis conditions (49.25 to 522  Oe).     

Growth of ZnSiP2 from tin solution and temperature composition diagram of the ZnSiP2: Sn system

ZnSiP₂ crystals (1 cm or more in length) have been grown from tin solution on a reproducible basis. The dimensions of the largest crystals obtained were 1.7×0.25×0.03 cm³ and 2×0.1×0.02 cm³. The temperature of the reaction region was 1050 to 1080° C and the cooling rate used to form these crystals was 7.5°C h^–1.A practical temperature-composition section of the ZnSiP₂:Sn phase diagram has been determined by differential thermal analysis, X-ray diffraction measurements and microscopic studies. The resulting information on the liquidus temperature variation with composition served to give better control of ZnSiP₂ growth from tin solution. It was concluded that ZnSiP₂ reacted eutectically with Sn and the eutectic composition was close to 100%.     

Low polarization resistance of Ni-Cu-Ce oxide anode synthesized by coprecipitation with tetramethylammonium carbonate for intermediate temperature SOFC

With little deviation from the metal cation stoichiometry in a starting metal nitrate solution, Ni-Cu-Ce oxide powders for intermediate temperature SOFC anodes were synthesized by coprecipitation using tetramethylammonium carbonate and decomposition of coprecipitated metal carbonates. The synthesized oxide powder was found to have a high surface area. A 30% Ni-30% Cu-40% Ce anode fired at a low temperature of 900 °C on a Ce_0.9Gd_0.1O_1.95 electrolyte provided low electrode polarization with an estimate of less than 0.1 Ω cm² at temperatures over 600 °C on wet 50% H₂ despite the Ni-Cu metallic phase in the anode was only 30% by volume.     

Thermal evolution and densification of R2O-SiO2 gels

R₂O-SiO₂ materials were prepared with 5 mol% of alkaline oxide by the sol-gel method. The gel-glass transition was achieved by treatment in air or in a controlled atmosphere. The samples present a silica network structure to which the alkaline ions are incorporated in a different way as compared to that of conventional glass. Material densification sets in around 350° C. In the temperature range between 500 and 600° C silica devitrification are produced together with condensation-polymerization of many silanol groups which form part of the material. Densification treatments in a helium atmosphere eliminate these residual groups.     

From tin oxalate to (Fe, Co, Nb)-doped SnO2: Sintering behavior, microstructural and electrical features

Highly reactive SnO₂-doped nanocrystalline powders with average particle size of 20 nm and specific surface areas above 30 m²/g were obtained through the polymeric precursor method with tin oxalate (SnC₂O₄) as a chloride-free precursor for SnO₂. Powders and sintered discs were characterized by means of X-ray powder diffraction (XRD), SEM and TEM. The influence of Co and Fe on the microstructure development and on the electrical properties of dense SnO₂-based ceramics was studied. Co and Fe species were found to decrease in more than 70 °C the sintering temperature of SnO₂ with respect to mixed oxide procedures. Secondary phases enriched in Co and Fe were detected and identified in sintered samples with XRD. Current-voltage curves were registered for electrical characterization. Doping with iron increased the electrical breakdown field and a nonlinearity coefficient of 20 was achieved.     

Deposition of indium tin oxide by atmospheric pressure chemical vapour deposition

We report the deposition of indium tin oxide (ITO) by atmospheric pressure chemical vapour deposition (APCVD). This process is potentially scalable for high throughput, large area production. We utilised a previously unreported precursor combination; dimethylindium acetylacetonate, [Me₂In(acac)] and monobutyltintrichloride, MBTC.[Me₂In(acac)] is a volatile solid. It is more stable and easier to handle than traditional indium oxide precursors such as pyrophoric trialkylindium compounds. Monobutyltintrichloride (MBTC) is also easily handled and can be readily vaporised. It is compatible with the process conditions required for using [Me₂In(acac)].Cubic ITO was deposited at a substrate temperature of 550 °C with growth rates exceeding 15 nm/s and growth efficiencies of between 20 and 30%. Resistivity was 3.5 × 10^− 4 Ω cm and transmission for a 200 nm film was > 85% with less than 2% haze.     

Reduction of interlayer Co2+ ions in fluorine mica using diethylene glycol

Reduction of interlayer Co²⁺ ions in expandable fluorine mica has been attempted. The polyol process using diethylene glycol as a reducing agent was employed. The co²⁺ -exchanged mica was refluxed at about 225–235 °C in liquid diethylene glycol for 10–120 minutes. Consequently, zero-valence Co metal (Co⁰) intercalated mica having a metallic grey colour was obtained by in situ reduction of interlayer Co²⁺ ions, showing different properties from Co²⁺ -exchanged mica as a precursor. The layer charge of Co-metal-intercalated mica is compensated by protons which are produced through the course of reduction of interlayer Co²⁺ ions. The reduced sample heated at 350 °C, which had no organic molecules, exhibited a basal spacing of 1.28 nm, indicating the presence of 0.34 nm cobalt metal clusters after subtracting the thickness of the host silicate layer. During the process of reduction in diethylene glycol, cobalt metal particles were expelled from the interlayers which grew to about 0.5 m onto the external surfaces of host mica crystals with increasing refluxing time.     

Elaboration of heterojunction solar cells by the deposit of tin oxide thin films on silicon by APCVD

We present in this paper the experimental results concerning the deposition of tin oxide SnO₂ on silicon substrate by the technique of Atmospheric Pressure Chemical Vapour Deposition (APCVD). The obtained Si-SnO₂ heterostructure is used for photovoltaic application. The properties of tin oxide thin films deposited by APCVD technique depends on three parameters which are the deposition temperature, the deposition time and the oxygen pressure. We have obtained the optimal value of each parameter by the measurement of the open-circuit voltage of the obtained Si-SnO₂ heterostructure. So, at the temperature of 490 °C during 12 min of deposition time under oxygen pressure of 1 bar we have obtained tin oxide thin layers exhibiting the best optoelectronic and morphology characteristics. These thin films are polycrystalline and present a resistivity of 1.3 · 10^− 3 Ω cm and a refractive index of 1.72. The Si-SnO₂ heterojunction solar cell that has an area of 2 × 1.5 cm² is characterised by the current-voltage I(V) measurement. It gives an open circuit voltage of 0.45 V and a short circuit current of 74 mA.     

Crystal modulation of tungsten oxide gels and films prepared by the sol-gel process using 2,4-pentanedione as an organic ligand

Tungsten oxide gels and films were prepared by the sol-gel process using 2,4-pentanedione (PTN) as an organic ligand. WO₃ powders were obtained by peeling the films from the quartz glass substrates. The crystal structure of both the gels prepared with and without PTN and fired at 700 °C was monoclinic. WO₃ powders peeled from film samples prepared both with and without PTN showed only the monoclinic crystal structure, whereas the crystal phases of both types of films were cubic and a mixture of cubic and monoclinic crystals, respectively. These results indicate that the cubic crystals of the WO₃ in the films were transformed to the monoclinic crystals of the powders after the films were peeled from the quartz glass substrates. It is concluded that the cubic crystals in the films are transformed to stable monoclinic crystals by the peeling process, whereas PTN and the quartz glass substrate can control the crystal phase of WO₃ films selectively to form the cubic structure.     

Preparation and crystallization of ultrafine Li2O-Al2O3-SiO2 powders

Ultrafine powders of Li₂O-Al₂O₃-SiO₂ (LAS) glass-ceramic were prepared by the sol-gel process using tetraethoxysilane, titanium butoxide, lithium, magnesium, aluminium (and zinc) inorganic salts as starting materials. The effect of pH on the sol-gel transition and particle sizes of the Li₂O-Al₂O₃-SiO₂ system was studied. The nucleation and crystallization process of LAS powders were also investigated by differential thermal analysis and X-ray diffraction. The results show that a surface nucleation process occurs for ultrafine LAS powders. The LAS glass-ceramics fabricated from ultrafine LAS powders have a low thermal expansion coefficient, <10×10^–7 °C.     

Effect of precursor solutions with different composition on synthesis of ultrafine BaLa0.3Fe11.7O19 using sol-gel auto-combustion technique

Hexagonal BaLa_0.3Fe_11.7O₁₉ ultrafine powders with a magnetoplumbite type (M-type) structure were synthesized by a sol-gel auto-combustion method. Precursor solutions with different composition were investigated to clarify the forming conditions of the ferrites. The crystal structure, grain size, form and magnetic properties were studied by means of X-ray diffraction (XRD), transmission electronic microscopy (TEM) and vibrating sample magnetometry (VSM). On the basis of analysing the effect of ammonia, citric acid and glycol on phase structure and magnetic properties, it was demonstrated that adjusting the pH value of the precursor solution with ammonia and adding an appropriate amount of citric acid and glycol are key steps in synthesis of ultrafine powders with single BaFe₁₂O₁₉ phase and excellent magnetic properties. In the presence of chelate agent (citric acid) and dispersant (glycol), under the conditions of pH about 7.0, nitrate/citric acid molar ratio of 1:3 and calcination temperature of 850°C (1 h), M-type BaLa_0.3Fe_11.7O₁₉ ultrafine powders with a particle size of about 36 nm, a specific magnetization s of 65.54 A · m²/kg and a coercive force Hc of 433 kA/m, were obtained.     

Synthesis of Bi2Fe4O9 via PVA sol-gel route

Bi₂Fe₄O₉ powders were synthesized by a sol-gel process using polyvinyl alcohol (PVA) as a complexing agent. Differential scanning calorimetry (DSC), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Field emission scanning electron microscope (FSEM) techniques were used to characterize precursor and derived oxide powders. The effect of the ratios of positively charged valences to hydroxyl groups of PVA (Mⁿ⁺/-OH) on the formation of Bi₂Fe₄O₉ was investigated. XRD analysis showed that single-phase Bi₂Fe₄O₉ was obtained from the Mⁿ⁺/-OH = 2:1 and Mⁿ⁺/-OH = 1:1 precursors at the temperature of 700 °C. For the precursor with Mⁿ⁺/-OH = 4:1, pure Bi₂Fe₄O₉ formed at the temperature of 800 °C. Bi₂Fe₄O₉ powders clacined at 700 °C from Mⁿ⁺/-OH = 2:1 precursor shows weak ferromagnetism.