Effect of pre-sintering temperature on the structural and dielectric properties of (Ba0.5Sr0.5)TiO3 thin films deposited by sol–gel technique

(Ba_0.5Sr_0.5)TiO₃ thin films have been deposited by sol–gel technique and the effect of pre-sintering temperature on the structural and dielectric properties has been studied. The sol was prepared from barium acetate and strontium acetate powders by dissolving them in acetic acid; while titanium isopropoxide was used as titanium source. Acetyl acetone, 2-methoxyethanol, and formamide were used as chelating agent, diluting reagent, and for getting crack free films, respectively. Two sets of films were prepared; one set pre-sintered at 400 °C while the other one at 600 °C. In all the cases, the final sintering temperature was kept fixed at 700 °C for 2 h. These films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dielectric constant, and loss measurements and AC conductivity studies. It has been found that with an increase in the pre-sintering temperature from 400 to 600 °C, the dielectric constant increases from 225 to 383 (measured at 100 kHz); whereas, the loss tangent remains nearly constant at 0.03–0.05. The XRD results show better crystallinity and enhanced grain growth in case of films pre-sintered at 600 °C. The FTIR spectra reveals that there is significant removal of organic materials in films with higher pre-sintering temperature as compared to that with lower pre-sintering temperature. The AC conductivity studies show a decrease in the frequency exponent ‘s’ with an increase in the pre-sintering temperature which has been correlated with the reduction in oxygen vacancy densities in the sample with higher pre-sintering temperature.     

Recrystallization of Oxygen Ion Implanted Ba0.7Sr0.3TiO3 Thin Films

The crystallization behavior of chemical-solution-deposited and amorphous Ba_0.7Sr_0.3TiO₃ (BST) thin films was analyzed with respect to the evolution of the structural and dielectric properties of the films as a function of the annealing temperature. The amorphous films were produced by oxygen ion implantation into crystalline BST thin films. In the amorphous thin films, the crystallization to the perovskite phase occurred at T = 550°C, whereas the as-deposited CSD films showed the first crystalline XRD-reflex only after annealing at T = 650°C. Here a carbon-rich intermediate phase delayed the crystallization process to higher temperatures.     

Metal-organic chemical liquid deposited (1 1 0)-preferred LaNiO3 buffer layer for Pb0.97La0.02(Zr0.85Sn0.13Ti0.02)O3 antiferroelectric films

Conductive perovskite lanthanum nickelate LaNiO₃ (LNO) thin films were fabricated on SiO₂/Si substrates through metal-organic chemical liquid deposition method. The effect of annealing temperature on the orientation and sheet resistance of the LNO films were investigated. XRD patterns showed that the LNO films deposited on SiO₂/Si substrates exhibited preferred-(1 1 0) orientation. The lowest sheet resistance of the LNO thin films, 250 Ω/□ was obtained after being annealed at 650 °C for 1 h. Subsequently, Pb_0.97La_0.02(Zr_0.85Sn_0.13Ti_0.02)O₃ (PLZST) antiferroelectric thin films were prepared on the LaNiO₃ buffered SiO₂/Si substrates via sol–gel process. And the crystallinity, microstructure and electric properties of the PLZST thin films were studied in details.     

Effects of LaNiO3 buffer layers on preferential orientation growth and properties of PbTiO3 thin films

(1 0 0)- and (1 0 1)-oriented PbTiO₃ (PT) thin films on conductive LaNiO₃ (LNO)-coated Si(1 1 1) substrates were prepared by a metal-organic decomposition method. It is found that the crystallization states of LNO thin films used as buffer layers have significantly effects on preferential orientation of PT thin films. PT thin films with (1 0 0) orientation could be obtained not only on the crystalline LNO (1 0 0) film, but also on the amorphous LNO thin film. The highly (1 0 0)-oriented PT films show high dielectric constant of 189.4 on LNO (1 0 0) films and 183.1 on amorphous LNO films. The PT capacitors fabricated on the LNO buffer layers display good P–E hysteresis loops. The remnant polarization (P_r) and coercive field (E_c) of PT films on amorphous, (1 0 0)- and (1 1 0)-oriented LNO films are 9.35 μC/cm² and 162.8 kV/cm, 10.03 μC/cm² and 163.3 kV/cm, 11.23 μC/cm² and 166.2 kV/cm, respectively.     

Characteristics of La2O3 thin films deposited using metal organic chemical vapor deposition with different oxidant gas

La₂O₃ films were deposited using O₃ and the structural and electrical properties were investigated and compared with those of La₂O₃ films deposited using O₂. The deposition temperature of the La₂O₃ films using O₃ was slightly reduced compared to that of the La₂O₃ films generated using O₂. After a post-annealing process at 600 and 900 °C, the crystallinity of the La₂O₃ films using O₃ were smaller than that using O₂. The leakage current density increased after annealing at 600 °C due to densification and then decreased after annealing at 900 °C due to interfacial layer growth. The effective dielectric constant of the La₂O₃ films deposited using O₃ decreased at 900 °C due to interfacial layer growth. The La₂O₃ films deposited using O₃ showed better structural and electrical properties in this study.     

Hydrophilic/hydrophobic conversion of Ni-doped TiO2 thin films on glass substrates

Nickel-doped titanium oxide thin films were prepared on soda–lime–silica glass substrates by using a metal naphthenate. Films prefired at 500 °C for 10 min were finally annealed at 600 °C for 30 min in air. Contact angle measurement was used for analyzing hydrophilic/hydrophobic conversion. NiTiO₃, rutile and anatase peaks were obtained for the film after nickel doping. The film containing nickel showed a shift towards the visible in the absorption threshold.     

Thermal evolution of Fe2O3-TiO2 sol-gel thin films

Fe₂O₃-TiO₂ thin films were deposited on silica glass slides using three sol-gel solutions containing Ti-butoxide and different iron oxide precursors. The thermal evolution of the coatings was followed by DTA-TGA and XRD from 200 to 1000°C. All the iron-containing samples were amorphous up to 700°C, when a phase separation between iron and titanium oxides was evidenced by the presence of crystalline Fe₂O₃. Above that temperature a titanate compound (pseudobrookite) formed according to the equilibrium phase diagram. The use of different precursors did not affect the thermal evolution and all the different samples exhibited the same trend.     

Crystallization and Photoactivity of Tio2 Films Formed on Soda Lime Glass by a Sol-Gel Dip-Coating Process

Transparent nanophase TiO₂ thin films on soda lime glass were prepared from titanium tetraisopropoxide (TTIP) by a sol-gel dip-coating method. The TiO₂ films had amorphous phase up to 400°C and anatase phase at 500°C. The amorphous TiO₂ films obtained at 300-400°C showed considerable photoactivity for the degradation of formic acid. The photoactivity of the TiO₂ films was enhanced with increasing calcination temperature from 300° to 500°C. The crystallinity of the anatase films at 500°C was improved with increasing calcination time up to 2 h and reduced with a further increase in calcination time to 4 h due to the significant formation of sodium titanate phase as a result of sodium diffusion. The four-time-dipping anatase films at 500°C exhibited the greatest photoactivity at the calcination time of 2 h. Sodium diffusion into TiO₂ films was retarded by a SiO₂ underlayer of 50 nm in thickness.     

Effects of Heating Profiles on the Orientation and Dielectric Properties of 0.5Pb(Mg1/3Nb2/3)O3-0.5PbTiO3 Thin Films by Chemical Solution Deposition

0.5Pb(Mg_1/3Nb_2/3)O₃-0.5PbTiO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by varying the film formation procedures and heating processes. Depending on the multilayer film formation and appropriate heating process, the films were grown with a preferential orientation. The films showed a (100)-preferred orientation and large grain-size distribution when they were directly heat-treated after deposition of amorphous layers. The films showed a (111)-preferred orientation and small grain-size distribution when formed layer-by-layer or directly heating amorphous thin films with a perovskite seed layer. These results were explained by the effect of a seed layer. Saturation polarization of the (111)-preferred films was ∼35 µC/cm², which was somewhat higher than that of the (100)-preferred film. In contrast, the dielectric constant of the (100)-preferred film was ∼1600, which was larger than that of the (111)-preferred film.     

Preparation and characterization of TiO2–SiO2 nano-composite thin films

TiO₂ nanocrystalline particles dispersed in SiO₂ have been prepared by the sol-gel method using titanium- and silicon-alkoxides as precursors. Nano-composite thin films were formed on the glass substrates by dip-coating technique and heat treated at temperatures up to 500 °C for 1 h. The size of the TiO₂ nanocrystalline particles in the TiO₂–SiO₂ solution ranged from 5 to 8 nm. The crystalline structure of TiO₂ powders was identified as the anatase phase. As the content of SiO₂ increased, the anatase phase tended to be stabilized to higher temperature. TEM results revealed the presence of spherical TiO₂ particles dispersed in a disk-shaped glassy matrix. Photocatalytic activity of the TiO₂–SiO₂ (1:1) thin films showed decomposition of 95% of methylene blue solution in 2 h and a contact angle of 10°. The photocatalytic decomposition of methylene blue increased and the contact angle decreased with the content of TiO₂ phase. TiO₂–SiO₂ with the molar ratio of 1:1 showed a reasonable combination of adhesion, film strength, and the photocatalytic activity.     

Effects of experimental parameters on the physical properties of non-stoichiometric sputtered vanadium nitrides films

Polycrystalline vanadium nitrides thin films were deposited onto (1 0 0)-oriented silicon wafers by reactive dc planar magnetron sputtering. The influence of the nitrogen gas flow (from 0 to 15 sccm) was studied. Several substrate temperatures were investigated: 150, 400 and 650 °C. Analytical techniques including X-ray diffraction and reflectivity, atomic force microscopy and optical photospectrometry were used to characterize the structure, the morphology and the optical properties of the films. The measured thickness indicates that the deposition rate is decreased (from 3.5 Å for 0 sccm to 1.5 Å for 15 sccm) with increasing nitrogen gas flow. Obtained structures depend on the substrate temperature. The structure of pure vanadium (0 sccm) varies from amorphous phase at 150 and 400 °C to -V phase at 650 °C. The films crystallize dominantly in β-V₂N_1−x phase at low nitrogen gas flows and in δ-VN_1−x phase at high nitrogen gas flows. The as-deposited VN films were highly textured. The texture seems to depend on the nitrogen gas flow. The root mean square (rms) derived from atomic force microscopy (AFM) varies with the nitrogen gas flow. The optical reflectivity of VN films shows high values in the infrared region.     

Temperature dependence of electrical and electromechanical properties of Pb(Mg1/3Nb2/3)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr,Ti)O3 thin films

The electrical and electromechanical properties of Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃ (PMN–PNN–PZT, PMN/PNN/PZT = 20/10/70) on Pt/Ti/SiO₂/Si substrates by chemical solution deposition was investigated. The PMN–PNN–PZT films annealed at 650 °C exhibited slim polarization hysteresis curves and a high dielectric constant of 2100 at room temperature. A broad dielectric maximum at approximately 140–170 °C was observed. The field-induced displacement was measured by scanning probe microscopy, the bipolar displacement was not hysteretic, and the effective piezoelectric coefficient (d₃₃) was 66 × 10⁻¹² m/V. The effective d₃₃ decreased with temperature, but the value at 100 °C remained 45 × 10⁻¹² m/V.     

Li diffusion in LiNi0.5Mn0.5O2 thin film electrodes prepared by pulsed laser deposition

Kinetic and transport parameters of Li ion during its extraction/insertion into thin film LiNi_0.5Mn_0.5O₂ free of binder and conductive additive were provided in this work. LiNi_0.5Mn_0.5O₂ thin film electrodes were grown on Au substrates by pulsed laser deposition (PLD) and post-annealed. The annealed films exhibit a pure layered phase with a high degree of crystallinity. Surface morphology and thin film thickness were investigated by field emission scanning electron microscopy (FESEM). The charge/discharge behavior and rate capability of the thin film electrodes were investigated on Li/LiNi_0.5Mn_0.5O₂ cells at different current densities. The kinetics of Li diffusion in these thin film electrodes were investigated by cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT). CV was measured between 2.5 and 4.5 V at different scan rates from 0.1 to 2 mV/s. The apparent chemical diffusion coefficients of Li in the thin film electrode were calculated to be 3.13 × 10⁻¹³ cm²/s for Li intercalation and 7.44 × 10⁻¹⁴ cm²/s for Li deintercalation. The chemical diffusion coefficients of Li in the thin film electrode were determined to be in the range of 10⁻¹²-10⁻¹⁶ cm²/s at different cell potentials by GITT. It is found that the Li diffusivity is highly dependent on the cell potential.     

Preparation, structural and optical characterization of BaWO4 and PbWO4 thin films prepared by a chemical route

Polycrystalline BaWO₄ and PbWO₄ thin films having a tetragonal scheelite structure were prepared at different temperatures. Soluble precursors such as barium carbonate, lead acetate trihydrate and tungstic acid, as starting materials, were mixed in aqueous solution. The thin films were deposited on silicon, platinum-coated silicon and quartz substrates by means of the spinning technique. The surface morphology and crystal structure of the thin films were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction, and specular reflectance infrared Fourier transform spectroscopy, respectively. Nucleation stages and surface morphology evolution of thin films on silicon substrates have been studied by atomic force microscopy. XRD characterization of these films showed that BaWO₄ and PbWO₄ phase crystallize at 500 °C from an inorganic amorphous phase. FTIR spectra revealed the complete decomposition of the organic ligands at 500 °C and the appearance of two sharp and intense bands between 1000 and 600 cm⁻¹ assigned to vibrations of the antisymmetric stretches resulting from the high crystallinity of both thin films. The optical properties were also studied. It was found that BaWO₄ and PbWO₄ thin films have Eg=5.78 eV and 4.20 eV, respectively, of a direct transition nature. The excellent microstructural quality and chemical homogeneity results confirmed that soft solution processing provides an inexpensive and environmentally friendly route for the preparation of BaWO₄ and PbWO₄ thin films.     

Aerosol deposition of dense lead zirconate titanate thin films at room temperature

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) films were grown on silicon 1 0 0 substrate by aerosol deposition, using solid-state reacted powder containing donor oxide Nb₂O₅, while the substrate was maintained at room temperature. The PZT films were simultaneously sintered upon deposition on a highly densified ceramic layer. Crystalline phases of the deposited films have been determined by X-ray diffractometry (XRD), and microstructures analysed by transmission electron microscopy (TEM). The cross-section microstructure consisted of several thin layers, including the PZT film and the platinum electrode and titanium-buffered layers on the substrate. High-resolution images revealed that the PZT layer contained a mixture of randomly oriented grains of nanometre size, which were embedded in an amorphous matrix. In contrast to the conventional liquid-phase sintering mechanism, sintering of the PZT films involved amorphised phases generated by pressure-induced amorphisation (PIA) from plastic deformation when the initial powder particles collided amongst one another upon reaching the silicon substrate during aerosol deposition. An analogy may be drawn to the impact of extraterrestrial meteorites in which diaplectic glass, i.e., amorphised phase, was formed and retained metastably at room temperature. The individual PZT grains were joined with the amorphised phase(s) and sintered to become a dense, thin film on the silicon substrate.     

Low temperature synthesis of MgxAl2(1−x)Ti(1+x)O5 films by sol–gel processing

Aluminium titanate films thicker than 0.5 μm have been synthesized by sol–gel methods. The films have been deposited via repetitive dip-coating on silicon wafers and their thermal stability has been tested as a function of the annealing time and temperature. The sol–gel approach has allowed the formation of the aluminium titanate phase at temperatures (700 °C) much lower than those necessary for solid-state reactions (1450 °C). Magnesium oxide has been used to improve the thermal stability of the films at high temperatures. The behavior of samples prepared with two different Mg content, i.e. Mg_0.2Al_1.6Ti_0.8O₅ and Mg_0.6Al_0.8Ti_1.6O₅, has been studied. The films have proven to be stable at 1150 °C, for up to 90 h. X-ray photoelectron spectroscopy has shown that after firing at 500 °C the surface chemical composition of the films is in accordance with the nominal one, whilst at higher annealing temperatures some differences, attributed to diffusion effects, have been observed.     

Catalytic performance of Co3O4/CeO2 and Co3O4/CeO2–ZrO2 composite oxides for methane combustion: Influence of catalyst pretreatment temperature and oxygen concentration in the reaction mixture

The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration (λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ containing 30 wt.% of Co₃O₄. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples).

Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g⁻¹ h⁻¹). The catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ were compared with those of two pure Co₃O₄ oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ as well as to their reducibility. Particular attention was paid to the thermal stability of the Co₃O₄ phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co₃O₄ heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co₃O₄ decomposition into CoO was observed.

Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co₃O₄ and by promoting the reduction at low temperature.     

Investigation of a Ba0.5Sr0.5Co0.8Fe0.2O3−δ based cathode SOFC: II. The effect of CO2 on the chemical stability

The effect of carbon dioxide on the chemical stability of a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ cathode in the real reaction environment at 450 °C was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), temperature programmed desorption (TPD), X-ray diffraction (XRD) and electrochemical impedance spectra (EIS) techniques. It was found that the presence even of very small quantities of CO₂ seriously deteriorates the fuel cell performance at 450 °C. XPS, TPD and XRD results strongly evidenced the formation of carbonates involving strontium and possibly barium after the BSCF cathode was operated in 1% CO₂/O₂ gas mixture at 450 °C for 24 h. SEM-EDX analysis of the BSCF cathode surface, after treatment in CO₂/O₂ environment at 450 °C, showed small particles on the surface probably associated with a carbonate phase and a segregated phase of the perovskite. The corresponding EDX spectra confirmed the presence of a carbonate layer and also revealed the surface enrichment of strontium and barium elements. EIS results indicated that both ohmic and polarization resistances increased gradually with the introduction of carbon dioxide in the oxidant stream, which could be interpreted by the decreased oxygen reduction kinetics and the formation of carbonate insulating layer.     

Syngas production from butane using a flame-made Rh/Ce0.5Zr0.5O2 catalyst

The capability of flame-made Rh/Ce_0.5Zr_0.5O₂ nanoparticles catalyzing the production of H₂- and CO-rich syngas from butane was investigated for different Rh loadings (0–2.0 wt% Rh) and two different ceramic fibers (Al₂O₃/SiO₂ and SiO₂) as plugging material in a packed bed reactor for a temperature range from 225 to 750 °C. The main goal of this study was the efficient processing of butane at temperatures between 500 and 600 °C for a micro-intermediate-temperature SOFC system. Our results showed that Rh/Ce_0.5Zr_0.5O₂ nanoparticles offer a very promising material for butane-to-syngas conversion with complete butane conversion and a hydrogen yield of 77% at 600 °C. The catalytic performance of packed beds strongly depended on the use of either Al₂O₃/SiO₂ or SiO₂ fiber plugs. This astonishing effect could be attributed to the interplay of homogeneous and heterogeneous chemical reactions during the high-temperatures within the reactor.     

Influence of molar ratio of citric acid to metal ions on preparation of La0.67Sr0.33MnO3 materials via polymerizable complex process

Polycrystalline La_0.67Sr_0.33MnO₃ (LSMO) nanometric sized powders and thin films are obtained from the resins synthesized by the polymerization of citric acid and ethylene glycol. Molar ratios of citric acid to metal ions were varied, and the resulting effects on the powder's properties were studied using TGA/DTA, FTIR, SEM and X-ray diffraction (XRD). The results indicated that with the molar ratio of citric acid/metal ions at 4, the resin contained a lower fraction of monodentate ligand and a higher portion of CCO structure obtained from ethylene glycol, which made it possible to synthesize the perovskite phase at temperature as low as 500 °C. The powder calcined at 550 °C exhibited a pure phase of perovskite, had a particle size of about 20–50 nm and a specific surface area of 25.24 m²/g. Thin films were prepared by using the as-prepared sols for spin coating on (1 0 0) Si substrate to investigate the properties of the films. As a result of the molar ratio of citric acid/metal cations at 3–4, the transformation of rhombohedral structure to cubic structure was observed.