Formation of cerium titanate,CeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>, in sol–gel films studied by XRD and FAR infrared spectroscopy

The process of formation of cerium titanate films as a function of annealing temperature and composition has been studied by combining X-ray diffraction analysis and far infrared spectroscopy. The films have been prepared by a sol–gel synthesis using metal chlorides as precursors; the synthesis allows obtaining cerium titanate films upon annealing in air. A brannerite type, CeTi₂O₆, phase has been identified by X-ray diffraction and Rietveld analysis on thin films. CeTi₂O₆ is formed upon annealing at 700 °C and in a limited range of ceria-titania mixed compositions. The far infrared spectra are useful to observe the formation of crystalline phases at the beginning of the crystallization process at lower firing temperatures, when the XRD analysis is not enough sensitive.     

Magneto-Optical Characteristics of Co, Ti-Substituted Barium Hexaferrite Films Deposited by the Dip-Coating Method

Pure and Co, Ti-substituted hexagonal barium ferrite (BaFe₁₂O₁₉, BaM) films were prepared by the dip-coating method from alkoxides. After repeated dipping, drying and calcining at 500°C for about 15 minutes in an oxygen atmosphere, polycrystalline films with a thickness of 1–1.8 μm on SiO₂ substrates were obtained. Spectral dependencies of the Faraday rotation and the optical transmission of BaCo _x Ti _x Fe_12−2x O₁₉(0≤x≤0.8) films were measured in the range from 500 to 2500 nm at room temperature. The absorption coefficient did not display much structure, but specific Faraday rotation spectra of Co, Ti-ferrite films showed local maxima at 720, 1475 and 1750 nm. At those wavelengths, the magneto-optical figure of merit attains its maximum values. For comparison of the crystallization and magnetic properties, Ba(CoTi) _x Fe_12−2x O₁₉ (x=0.9) powder has also been prepared by the sol-gel method.     

Preparation of super-hydrophobic white carbon black from nano-rice husk ash

Nano-rice husk ashes were prepared by burning rice husk with a self-propagating method. The white carbon black with high purity was prepared by an alkali dissolving–acid reaction method from nano-husk ash. The super-hydrophobic SiO₂ films were prepared by the sol–gel method using hexamethyldisilazane as a modifier. The effects of the pH and reaction time in the acid reaction process on the purity of the white carbon black, and the effect of the modifier on the hydrophobic property of SiO₂ films were studied. The performances were characterized by XRD, BET, SEM, IR, and contact angle analyzer. The results showed that the purity of white carbon black reached 98.48 % when the NaOH solution with the rice husk ash was heated for 2 h at 90 °C, then the pH of the solution was adjusted by sulfuric acid to 3, and the acid reaction time was 2 h. The contact angle of SiO₂ films was more than 160° when volume ratio of the modifier to silica–sodium hydroxide mixed solution was 0.15. The mechanism of the modifier on SiO₂ surfaces is a graft copolymerization. The hydrophobic groups in the modifier replace the hydroxy groups on SiO₂ surfaces and make SiO₂ surfaces present super-hydrophobicity.     

Role of reaction atmosphere in preparation of potassium tantalate through sol–gel method

Potassium tantalate (KT) thin films and powders of both K₂Ta₂O₆ (KT pyrochlore) and KTaO₃ (KT perovskite) structures were prepared by means of chemical solution deposition method using Si(111) with ZnO and MgO buffer layers as a substrate. The influence of reaction atmosphere on reaction pathway and phase composition for both KT powders, and KT thin films has been studied mainly by means of powder diffraction and infrared spectroscopy. When an oxygen flow instead of static air atmosphere has been used the process of pyrolysis in oxygen runs over much narrower temperature interval (200–300 °C), relatively to air atmosphere (200–600 °C) and almost no (in case of powders), or no (in case of thin films) pyrochlore intermediate phase has been detected in comparison with treatment in air, where the pyrochlore phase is stable at temperatures 500–600 °C (powders). KT perovskite phase starts to crystallize at temperatures 50° and 150 °C lower compared to air atmosphere in case of powders and thin films, respectively. Microstructure formed by near-columnar grains and small grains of equiaxed shape was observed in films treated in oxygen and air atmosphere, respectively.     

Substrate temperature effects on the structural,compositional, and electrical properties of VO2 thin films deposited by pulsed laser deposition

The vanadium dioxide (VO₂) thin films were deposited on silicon (100) substrate using the pulsed laser deposition technique. The thin films were deposited at different substrate temperatures (500°C, 600°C, 700°C, and 800°C) while keeping all the other parameters constant. X‐ray diffraction confirmed the crystalline VO₂ (B) and VO₂ (M) phase formation at different substrate temperatures. X‐ray photoelectron spectroscopy analysis showed the presence of V⁴⁺ and V⁵⁺ charge states in all the deposited thin films which confirms that the deposited films mainly consist of VO₂ and V₂O₅. An increase in the VO₂/V₂O₅ ratio has been observed in the films deposited at higher substrate temperatures (700°C and 800°C). Scanning electron microscope micrographs revealed different surface morphologies of the thin films deposited at different substrate temperatures. The electrical properties showed the sharp semiconductor to metal transition behavior with approximately 2 orders of magnitude for the VO₂ thin film deposited at 800°C. The transition temperature for heating and cooling cycles as low as 46.2°C and 42°C, respectively, has been observed which is related to the smaller difference in the interplanar spacing between the as‐deposited thin film and the standard rutile VO₂ as well as to the lattice strain of approximately −1.2%.     

Processing and Characterization of Sol-Gel Derived Modified PbTiO3 for Ferroelectric Composite Applications

Powders of (Pb_0.8Ca_0.2)(Ti_0.99Mn_0.01)O₃ have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m²K and a pyroelectric figure of merit (FOM_p=p/ε) of 0.51 μC/m²K.     

Alkoxide Derived SrBi2Ta2O9 Phase Pure Powder and Thin Films

Phase pure powder and thin films of the novel ferroelectric materials SrBi₂Ta₂O₉ (SBT) have been prepared using the organic precursors. The xero-gel formed was dried and characterized using TGA and DTA to determine the organic burn out and crystallization temperature of SBT. Powder X-ray diffraction was used systematically to check the crystallinity of SBT. Phase pure SBT powder was formed as low as 650°C and thin films at 600°C in comparison to other earlier reported work. SEM micrographs show a grain size of ≈0.1 μm and show crack free films with a film thickness of 2 μm.     

The effect of different substrate temperatures on the structure and luminescence properties of Y2O3:Bi3+ thin films

Y₂O₃:Bi³⁺ phosphor thin films were prepared by pulsed laser deposition in the presence of oxygen (O₂) gas. The microstructure and photoluminescence (PL) of these films were found to be highly dependent on the substrate temperature. X-ray diffraction analysis showed that the Y₂O₃:Bi³⁺ films transformed from amorphous to cubic and monoclinic phases when the substrate temperature was increased up to 600 °C. At the higher substrate temperature of 600 °C, the cubic phase became dominant. The crystallinity of the thin films, therefore, increased with increasing substrate temperatures. Surface morphology results obtained by atomic force microscopy showed a decrease in the surface roughness with an increase in substrate temperature. The increase in the PL intensities was attributed to the crystallinity improvement and surface roughness decrease. The main PL emission peak position of the thin films prepared at substrate temperatures of 450 °C and 600 °C showed a shift to shorter wavelengths of 460 and 480 nm respectively, if compared to the main PL peak position of the powder at 495 nm. The shift was attributed to a different Bi³⁺ ion environment in the monoclinic and cubic phases.     

Electrochemical and Structural Characterisation of Dip-Coated Fe/Ti Oxide Films Prepared by the Sol-Gel Route

Thin solid films of mixed Fe/Ti oxide composition (Fe/Ti molar ratios: 0.5∶1, 1∶1, 1.5∶1) have been made from Fe(NO₃)₃ alcoholic solution to which Ti(OiPr)₄ was added. Films have been deposited by the dip-coating technique and heat-treated at 300°C and 500°C. Powders of Fe/Ti oxide heat-treated at 300°C are amorphous, while powders annealed at 500°C for 40 hours transformed to mixed rutile, pseudobrookite and hematite phases. The structure of the XRD amorphous films was identified with the help of near-normal reflection absorption (6°) (IRRA) and near-grazing incidence angle (NGIA) spectroscopy. NGIA FT-IR spectra of films are characterised with a single phonon mode appearing in the spectral range 600–950 cm⁻¹ which shifts with increasing Ti concentration from 675 cm⁻¹ (Fe₂O₃) to 904 cm⁻¹ (TiO₂) thus exhibiting one-mode behavior. Electrochemical investigations made with the help of cyclic voltammetry (CV) and chronocoulometry (CPC) performed in 0.01M LiOH and in 1M LiClO₄/propylene carbonate electrolytes revealed that films are able to uptake reversibly Li⁺ ions with a charge capacity (Q) per film thickness (d) in the range 0.1–0.26 mC/cm²nm and 0.06 mC/cm²nm, respectively. The temperature at which the films were prepared alters the rate of Li⁺ insertion which is faster for less compact films obtained at 300°C. In situ UV-VIS spectroelectrochemical measurements revealed that Fe/Ti oxide films bleached in the UV spectral region (300 nm<λ<450 nm) and colored in the VIS spectral region (450 nm<λ<800 nm), thus exhibiting mixed anodic and cathodic electrochromism.     

Synthesis and description of SrSn0.6Ln0.4O3 perovskite pigments

Inorganic pigments containing lanthanides based on pseudo cubic structure of SrSnO₃ have been prepared by solid state reaction between SrCO₃, SnO₂ and lanthanide oxides (Tb₄O₇, Pr₆O₁₁, CeO₂) in the temperature range 1300–1550°C. The resultant materials were characterised by XRD, TG-DTA and colourimetric techniques were used. The most interesting colour properties were provided by SrTb_0.4Sn_0.6O₃ prepared by firing at temperature 1500°C which has light yellow-green colour hue. The increase of temperature 1300–1500°C caused the creation of pigments with deeper and brighter colour hue. Colour properties of the samples prepared by calcination at 1550°C were of inferior quality due to structural changes from pseudo cubic to orthorhombic system.     

Effect of sintering temperature on the structural, optical and electrical properties of sol–gel derived indium oxide thin films

Sol gel derived indium oxide, In₂O₃; films were prepared by spin coating technique. The films were dried and sintered at different sintering temperatures (300, 400, 450 and 500 °C) in air. The effect of sintering temperature on the structural, optical and electrical properties of In₂O₃ thin films was studied. The morphology and structure of the films were analyzed by scanning electron microscope and X-ray diffraction. The films showed a bcc structure that changes its 400-preferential orientation to 222 orientation as the sintering temperature increases from 300 to 500 °C. The optical behavior of the films was studied by measuring the transmission spectra in the wavelength range 200–2,500 nm. Different optical models have been proposed for fitting the transmittance data and simulate the optical constants as well as the film thickness of In₂O₃ films. The best fitting of the data was obtained by combining the classical Drude and OJL models coupled with the Bruggeman effective medium approximation. The optical parameters of Drude model (plasma frequency and damping constant) are used calculate the electrical properties of the films. The calculated values of the electrical sheet resistance were compared with those measured experimentally by four probes. The correlation between the film orientation change and its optical and electrical properties was discussed.     

Effects of annealing on the structural,electrical and optical properties of reactively evaporated thin fdlms of indium oxide

Thin films of indium oxide were prepared by thermal reactive evaporation of a mixture of indium oxide and metallic indium. This work is an experimental study of the modifications induced by an annealing treatment, on the structural, electrical and optical properties of indium oxide (In₂O₃). The results show important changes of different parameters determined after annealing. The films obtained after annealing at 350 °C for 3 hours under oxygen atmosphere have a good cristallinity. These films showed a transmittance of more than 80% in the visible region and a conductivity >10³ (Ω.cm)⁻¹.     

Cu-particle-dispersed (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> composite thin films derived from sol–gel processing

Sol–gel processing of Cu-particle-dispersed (K_0.5Na_0.5)NbO₃ (Cu/KNN) thin films was studied in an attempt to develop a method producing piezoelectric composite films with good mechanical performance. The Cu/KNN films were prepared via crystallization annealing at 650–750 °C for 1 min in air, followed by reduction annealing at 400–500 °C for 1–2 h in a 5% H₂ and 95% Ar gas mixture. The resultant composite films consisted of perovskite KNN, metallic Cu, and Cu₄O₃. This suggests that the decomposition of Cu sources takes two different ways in this study. The Cu/KNN composite films containing Cu₄O₃ phases were produced by the crystallization annealing at 700 °C for 1 min followed by the reduction annealing at 500 °C for 1 h. Surface morphology observations reveal that these films have dense KNN matrix with a grain size of ~200 nm and uniformly dispersed Cu or Cu₄O₃ particles with a size of <500 nm.     

Preliminary results on sol-gel processing of 〈100〉 oriented Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> thin films using diol-based solutions

A novel sol-gel method is used here for the synthesis of air-stable and precipitate-free diol-based sols of 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT). Sols containing a 15 mol% lead excess have been used for the preparation of PMN-PT thin films. The films were deposited onto (111)Pt/TiO₂/SiO₂/(100)Si substrates, and crystallised in oxygen by Rapid Thermal Processing (RTP), using different temperatures and soaking times. Single perovskite films are obtained when treated at temperatures between 600 and 700°C for 6 s. Those crystallised at other temperatures contain a secondary pyrochlore phase. This phase also appears in the films treated at 650°C with soaking times longer than 6 s. PMN-PT films with a 〈100〉 preferred orientation were prepared by using a PbTiO₃ seeding layer onto the substrate. These PMN-PT films present relaxor-type electrical properties. Dielectric permittivity, , shows significant dispersion. Its temperature dependence presents a broad maximum at 110–130°C, which position shifts towards higher temperatures with frequency. Ferroelectric hysteresis loops show high values of saturation polarisation but very low remanence. The piezoelectric activity of the films has been tested by the measurement of their local piezoelectric hysteresis loops.     

Preparation and characterization of CuAlO2 transparent thin films prepared by chemical solution deposition method

CuAlO₂ thin films were prepared on quartz glass and sapphire substrates by chemical solution deposition method using copper acetate monohydrate, aluminum nitrate nonahydrate and 2-methoxyethanol as starting precursor and solvent. The effects of annealing temperature on the structural, morphological, electrical and optical properties have been studied. Via the optimized annealing treatment condition, CuAlO₂ film annealed at 850 °C in nitrogen flow of 400sccm under atmosphere pressure exhibits the best performance with the lowest room temperature resistivity of 3.6 × 10² Ω cm and the highest optical transmission in the visible region (>70% at around 600 nm wavelength). CuAl₂O₄ and CuO phases, not CuAlO₂ phase are obtained when annealing temperature is lower than 850 °C. However, a further increase of annealing temperature weakens the crystallization quality and deteriorates the surface morphology of CuAlO₂ films as the annealing temperature exceeds 850 °C, leading to an increase in the resistivity and a decrease of the optical transmission in the visible region of CuAlO₂ films.     

The microstructure and magnetic properties of Ni<Subscript>0.4</Subscript>Zn<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> films prepared by spin-coating method

Nickel zinc ferrite (Ni_0.4Zn_0.6Fe₂O₄) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni_0.4Zn_0.6Fe₂O₄ films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M _s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H _c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M _s of 349 emu/cc and low coercivity H _c of 66 Oe. The M _s is higher than others which prepared by this method, however, the H _c is lower. The M _s of Ni_0.4Zn_0.6Fe₂O₄ films annealed at 700 °C increases with increasing annealing time and the H _c changes slightly.     

Determination of diffusion induced concentration profiles in Cr2O3 films on ceramic Al2O3 by Auger sputter depth profiling

Annealing induced interface and bulk effects in thin Cr₂O₃ films on aluminum oxide have been studied. The investigated samples have been prepared by reactive r.f. magnetron sputter deposition of Cr₂O₃ on ceramic Al₂O₃ substrates. Annealing at temperatures up to 1250° C have been carried out in situ under ultra high vacuum. Temperature induced compositional changes have been subsequently determined by AES sputter depth profiling without breaking the vacuum. The non-conducting substrates and the overlap of the Cr-(LMM)- and O-(KLL)-Auger peaks required special analysis parameters and spectra interpretation to obtain the concentration depth profiles of the different elements (Al, O, Cr).     

The sensor properties of Fe2O3 · In2O3 films: The detection of low ozone concentrations in air

The detection of low ozone concentrations in air (no higher than 120 ppb) using semiconducting films based on Fe₂O₃ · In₂O₃ obtained by laser ablation of the corresponding targets onto alumina substrates was studied. The temperature of the substrate during film deposition influenced their sensor properties. Temperature effects on the sensitivity of the films with respect to ozone were studied over the temperature range 200–380°C. Maximum sensitivity was reached at 250°C irrespective of the temperature of film deposition. The dependence of film sensitivity on the concentration of ozone in air was determined. At equal ratios between In₂O₃ and Fe₂O₃, the sensitivity of the sensor films prepared by laser ablation was much higher than that of thick-film sensors obtained from aqueous metal oxide suspensions by the stenciling technique. Possible reasons for the effects observed were considered.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Synthesis and Properties of Rb6Mn2O6

Rb₆Mn₂O₆ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn₃O₄, RbN₃ and RbNO₃) were heated in a special regime up to 500 °C and annealed at this temperature for 75 h in silver crucibles. Single crystals have been grown by annealing a mixture with a slight excess of rubidium components at 450 °C for 500 h. According to the single crystal structure analysis, Rb₆Mn₂O₆ is isotypic to K₆Mn₂O₆, and crystallizes in the monoclinic space group P2₁/c with a = 6.924(1) Å, b = 11.765(2) Å, c = 7.066(1) Å, β = 99.21(3)°, 2296 independent reflections, R₁ = 5.23 % (all data). Manganese is tetrahedrally coordinated and two tetrahedra are linked by sharing a common edge, forming a dimer [Mn₂O₆]⁶⁻. The magnetic behavior has been investigated.