Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films

VO₂ thin films were deposited on soda lime glass substrates with ZnO, TiO₂, SnO₂, and CeO₂ thin films applied as buffer layers between the VO₂ films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO₂ film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO₂ film, which was confirmed by XRD spectra. By using ZnO, TiO₂, and SnO₂ buffer layers, monoclinic VO₂ (VO₂(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO₂(B), which is known to have no phase transition near room temperature, were formed rather than VO₂(M) when the film was deposited on CeO₂ buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO₂, and SnO₂ buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO₂ film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO₂ films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO₂. Moreover, the degree of crystallization of buffer layer is also related with that of VO₂ film, and thus ZnO can be one of the most effective buffer layer materials.     

Epitaxial 0.65PbMg1/3Nb2/3O3-0.35PbTiO3 (PMN-PT) thin films grown on LaNiO3/CeO2/YSZ buffered Si substrates

Ferroelectric PMN-PT thin films with a thickness of 600 nm were epitaxially grown on buffered Si (0 0 1) substrates at a substrate temperature that ranged from 550 to 700 °C using pulsed laser deposition (PLD). LaNiO₃ (LNO) electrode thin films with a resistivity of ∼1900 μΩ cm were epitaxially grown on CeO₂/YSZ buffered Si (0 0 1) substrates. The PMN-PT thin films grown at 600 °C on LNO/CeO₂/YSZ/Si substrates had a pure perovskite and epitaxial structure. The PMN-PT films exhibited a high dielectric constant of about 1818 and a low dissipation factor of 0.04 at a frequency of 10 kHz. Polarization-electric-field (P-E) hysteresis characteristics, with a remnant polarization of 11.1 μC/cm² and a coercive field of 43 kV/cm, were obtained in the epitaxial PMN-PT films.     

Residual stress analysis of multi-layered buffer layers on Ni substrate for YBCO coated conductor

CeO₂/YSZ/CeO₂ buffer layer structure is one of the preferred buffer layers for fabrication of coated conductors. Textured CeO₂/YSZ/CeO₂ buffer layers are grown on biaxially textured Ni (100) substrate from the solution of Zr, Y, and Ce based organometalic compounds, solvent and chelating agent using reel-to-reel sol-gel technique. The film thickness is controlled by number of coating withdrawal speed and solution chemistry. Residual stresses arise during the manufacturing process of buffer layers depending on some factors. One of the most important is due to temperature variation. Effects of the temperature variation and coating thickness on residual stress in CeO₂/YSZ/CeO₂ buffer layers structure annealed at high temperature are analyzed theoretically. It is observed that the stress magnitudes reach high levels in the region of interlayer of different materials. The surface morphologies and microstructure of sample are characterized by ESEM and AFM. ESEM and AFM micrographs of the films revealed pinhole-free, crack-free, smooth and dense microstructures in the used manufacturing process.     

Effect of H2/CO2 mixture gas treatment temperature on the activity of LaNiO3 catalyst for hydrogen production from formaldehyde aqueous solution under visible light

H₂/CO₂ mixture gas treatment at moderate temperature is found to be effective in improving the activity of LaNiO₃ catalyst for hydrogen production from formaldehyde aqueous solution under visible light. The LaNiO₃, as a precursor, was treated at various temperatures (573–973 K) for 4 h under continuous flow mixture gas with a molar ratio of H₂/CO₂ = 4:1. Among all the resultant photocatalyst, the LaNiO₃ treated at 773 K (Ni/LaNiO_3?δ–La₂O₂CO₃), exhibited highest photocatalytic activity when exposed to visible-light irradiation and was further characterized by XRD, SEM, TEM, UV-diffuse reflectance spectroscopy. The results indicated that Ni/LaNiO_3?δ–La₂O₂CO₃ photocatalyst had narrow bandgap and can efficiently transfer photogenerated electrons on the surface and thus reduce H⁺ to hydrogen.     

Nanostructure and performance of Pt–LaNiO3 composite film for ferroelectric film devices

A conductive composite film of LaNiO₃ containing 36.1 at.% Pt was fabricated by radiofrequency co-sputtering. The film consists of two individual phases of separated LaNiO₃ and Pt. X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analysis reveal a net-like nanostructure characterized by 5 nm Pt grains embedded in the LaNiO₃ matrix. Temperature-dependent resistivity measurement indicates a weak electron–phonon interaction and strong electron–electron scattering in the film. BaTiO₃ film deposited on the composite film exhibits an increased remnant polarization due to release of interfacial charge accumulation, which indicates that the present conductive composite layer can be used as a promising electrode buffer layer in preparing ferroelectric film devices.     

Development of nano CeO2-incorporated high performance hot-dip zinc coating

Nano CeO₂ composite has been synthesized and explored as an effective activator for enhancing galvanic performance of hot-dip zinc coatings. The pre-treatment conditions and bath composition were optimized based on preliminary test results. Particle size of the CeO₂ was characterized by XRD and TEM analyses. Various electrochemical techniques such as OCP decay measurements, Anodic polarization, Salt spray analysis and Electrochemical Impedance Spectroscopy (EIS) were adopted to evaluate galvanic performance of the CeO₂-incorporated coatings. The coating incorporated with an optimum amount of CeO₂, i.e. 0.1%, exhibited best galvanic performance. The incorporation of CeO₂ caused significant improvement in galvanic and other physical characteristics of the coatings. It also resulted in lowering of the alloying reaction between zinc and iron, but enhanced barrier protection of the interior layers.     

The influence of reactive-element coatings on the high-temperature oxidation of pure-Cr and high-Cr-content alloys

The influence of various reactive-element (RE) oxide coatings (Y₂O₃, CeO₂, La₂O₃, CaO, HfO₂, and Sc₂O₃) on the oxidation behavior of pure Cr, Fe–26Cr, Fe–16Cr and Ni–25Cr at 900°C in O₂ at 5×10^–3 torr has been investigated using the¹⁸O/SIMS technique. Polished samples were reactively sputtercoated with 4 nm of the RE oxide and oxidized sequentially first in¹⁶O₂ and then in¹⁸O₂. The effectiveness of each RE on the extent of oxidation-rate reduction varied with the element used. Y₂O₃ and CeO₂ coatings were found to be the most beneficial, whereas Sc₂O₃ proved to be ineffective, for example, for the oxidation of Cr. SIMS sputter profiles showed that the maximum in the RE profile moved away from the substrate-oxide interface during the early stages of oxidation. After a certain time the RE maximum remained fixed in position with respect to this interface, its final relative position being dependent on the particular RE. The position of the RE maximum within the oxide layer also varied with the substrate composition. For all coatings¹⁸O was found to have diffused through the oxide to the substrate-oxide interface during oxidation, the amount of oxide at this interface increasing with increasing time. The SIMS data confirm that for coated substrates there has been a change in oxidegrowth mechanism to predominantly anion diffusion. The RE most probably concentrates at the oxide grain boundaries, generally as the binary oxide (RE) CrO₃. Cr³⁺ diffusion is impeded, while oxygen diffusion remains unaffected.     

Electrodeposition of cerium oxide films and composites

Nanostructured CeO₂ films were prepared by cathodic electrolytic deposition (ELD) and electrophoretic deposition (EPD). Benzoic acid has been utilized for the dispersion and charging of CeO₂ nanoparticles for EPD. The kinetics of ELD and EPD was investigated. Electrodeposition method has been developed for the deposition of poly(2-vinylpyridine) (PVP) films. The thickness of the films was varied in the range of 0.1-3 μm. The deposition mechanism was based on the pH increase in the cathodic reactions, electrophoresis of the protonated PVP macromolecules, neutralization of their charge and film formation at the cathode surface. The deposition yield was studied by the quartz crystal microbalance method. Two electrochemical strategies were developed for the fabrication of composite PVP-CeO₂ films, which were based on the electrodeposition of PVP and ELD or EPD of CeO₂. The composite films were studied by electron microscopy, X-ray diffraction, thermogravimetric and differential thermal analysis. The CeO₂ content in the composite films was varied by the variation of bath composition. The deposition methods allowed the fabrication of crack-free PVP-CeO₂ films, which provided corrosion protection of stainless steel substrates in aqueous NaCl solutions.     

Effect of different fillers on oxidation behavior of low-temperature chromizing coating

Three different chromizing coatings were produced on Ni substrate using a conventional pack-cementation method with Al₂O₃, Al₂O₃+CeO₂ and CeO₂ acting as filler, respectively, at a greatly decreased temperature (700 °C). Effects of different fillers on the isothermal and cyclic oxidation resistance of chromizing coating in air at 850 °C were comparably investigated. Microstructure results show that the addition of CeO₂ into the filler significantly retards the grain growth of the chromizing coating. Oxidation results indicate that the chromizing coating using CeO₂ as filler exhibits somewhat increased oxidation resistance than the normal chromizing coating, while the chromizing coating using Al₂O₃+CeO₂ as filler exhibits much better oxidation resistance. The effects of different fillers on the oxidation behaviors were discussed in detail.     

Selective catalytic reduction of NO with propene over Au/CeO2/Al2O3 catalysts

Selective catalytic reduction of NO by propene under an oxygen-rich atmosphere has been investigated over Au/ CeO₂, Au/CeO₂/Al₂O₃ and Au/Al₂O₃ catalysts prepared by deposition-precipitation. The results demonstrated that Au/16%CeO₂/Al₂O₃ had good low-temperature activity, selectivity towards N₂ and stability, which is superior to that of Pt/Al₂O₃. It was also found that adding 2% water vapour to the feed stream enhanced the NO conversions at low temperatures while the presence of 20 ppm SO₂ increased NO conversions at higher temperatures. It is particularly interesting that under the simultaneous presence of 2% water vapour and 20 ppm SO₂, the NO conversions to N₂ were significantly increased and the temperature window was widened significantly. The catalysts were characterized by Xray diffraction (XRD), high resolution transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (HRTEM-EDX) and temperatureprogrammed reduction (H2-TPR) techniques. Both XRD and HRTEM revealed that CeO₂ was highly dispersed on the alumina support, and HRTEM combined with EDX showed that gold particles were preferentially deposited on those highly dispersed CeO₂ particles. The gold deposition made CeO₂ more reducible and interaction between gold and those highly dispersed CeO₂ particles became stronger than that with the bulk CeO₂, and this interaction is probably responsible for the superior catalytic performance of the Au/CeO₂/Al₂O₃.     

Corrosion protection properties of cerium layers formed on tinplate

Corrosion protection properties of cerium-passivated, unpassivated and chromium-passivated tinplates in contact with a 0.1 M citric-citrate buffer solution were studied using polarisation (DC) and electrochemical impedance spectroscopy (EIS) methods. The morphology and composition of the passive layer were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) in conjunction with argon-ion sputtering. Cerium-passivated tinplate showed similar corrosion properties to chromium-passivated tinplate in DC measurements, while the latter yielded the best corrosion resistance results in EIS measurements. SEM and EDX illustrated spherical particles with iron, cerium and tin contributions. XPS measurements indicated that the cerium-rich coating was a hydrated oxide with a composition of cerium(III): Ce(OH)₃ and cerium(IV): CeO₂ and Ce(OH)₄.     

Solution-based synthesis of oxide thin films via a layer-by-layer deposition method: Feasibility and a phenomenological film growth model

The feasibility and kinetics of a generic layer-by-layer thin film deposition method are investigated using Y₂O₃-doped ZrO₂, pure ZrO₂, and Gd₂O₃-doped CeO₂ as model systems. Uniform nanocrystalline films have been made via dipping substrates alternately in cationic and anionic precursor solutions. The effects of several key processing parameters, including the number of deposition cycles, cationic concentration, dipping speed, and holding/immersing time, have been investigated. Growth rates of ∼ 4-12 nm per deposition cycle for as-deposited films (i.e., ∼ 2-6 nm/cycle for annealed films), tunable via varying the key deposition parameters, have been demonstrated.     

Cyclic Oxidation Behavior of Electrodeposited Ni3Al–CeO2Base Coatings at 850°C

The cyclic-oxidation behavior of electrodeposited pure, nano CeO₂ (9–15 nm)- and micron CeO₂ (5 μm)-modified Ni₃Al coatings on Fe–Ni–Cr substrates have been investigated at 850°C for periods up to 1000 hr. All the coatings showed good oxidation resistance in the early stage, but decreased oxidation protection during the intermediate stage of exposure. The formation of slow-growing γ-Al₂O₃ scales provided the coatings with good oxidation resistance in the early stage. However, a high volume fraction of pores in the coatings decreased oxidation resistance in the intermediate stage by forming oxidized channels between the pores. After long-term exposure, however, the pores in the coatings were healed by coating–substrate interdiffusion, and an improvement in cyclic-oxidation resistance was observed. The CeO₂ particles in the coating affected the stability of the protective oxide scale and the pore-healing behavior. The most significant effect was from nano size CeO₂ particles, which improved the stability of the protective oxide scale but retarded the rate of pore healing.     

Influence of the structure of TiO<Subscript>2</Subscript>, CeO<Subscript>2</Subscript>, and CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> supports on the activity of Ru catalysts in the catalytic wet air oxidation of acetic acid

Ru catalysts, supported on TiO₂, CeO₂, and CeO₂-TiO₂, were prepared by the impregnation method. The effect of the structure of the supports on the activity of Ru catalysts was investigated in the catalytic wet air oxidation (CWAO) of acetic acid under 230°C and 5 MPa in a batch reactor. Physical properties including the surface area, crystalline phase, and surface components of the Ru catalysts were characterized by N₂ adsorption, X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The CeO₂-based Ru catalysts had good activity, and the prepared RuO₂/CeO₂ catalyst showed markedly higher activity than the RuO₂/CeO₂-TiO₂ catalyst. The surface structure, the high amount of chemisorbed oxygen on the catalyst surface, and the suitable pH_pzc value of the supports played an important role in the activity of the Ru catalysts in CWAO of acetic acid.     

Enhanced corrosioon resistance by sol‐gel‐based ZrO2‐CeO2 coatings on magnesium alloys

The physical, chemical and mechanical properties of magnesium alloys make them attractive materials for automotive and aerospace applications. However, these materials are susceptible to corrosion and wear. This work discusses the potential of using sol‐gel based coatings consisting of ZrO₂ and 15 wt.% of CeO₂. The CeO₂ component provides enhanced corrosion protection, while ZrO₂ impart corrosion as well as wear resistance. Coating deposition was performed by the dip coating technique on two magnesium alloy substrates with different surface finishes: AZ91D (as‐casted, sand‐blasted, and machined) and AZ31 (rolled and machined). All as‐deposited coatings (xerogel coatings) were then subjected to 10 h annealilng: a temperature of 180°C was applied to the AZ91D alloy and 140°C to the AZ31 alloy. Morphological and structural properties of the annealed coatings were investigated by scanning electron microscopy, atomic force microscopy and transmission electron microscopy. Coating composition was examined using energy dispersive X‐ray analysis. Adhesion of the annealed ZrO₂‐CeO₂ coatings on the substrates, assessed by scratch tests, showed critical loads indicative of coating perforation of up to 32 N. Hardness and elasticity, measured using depth‐sensing nanoindentation tests, gave a hardness and elastic modulus of 4.5 GPa and 98 GPa, respectively. Salt spray corrosion tests performed on these coatings showed superior corrosion resistance for AZ91D (as‐casted and machined) and AZ31 (machined), while severe corrosion was observed for the AZ31 (rolled) and AZ91D (sand‐blasted) magnesium alloy substrates.     

La2O3/CeO2颗粒尺寸对Ni-La2O3/CeO2复合电镀层高温氧化性能的影响（英文）

通过向普通硫酸镍电镀液中添加一定含量的微米或纳米La2O3/CeO2颗粒,采用复合电镀制备微米或纳米La2O3/CeO2颗粒分布的Ni基复合镀层,并研究La2O3/Ce O2颗粒尺寸对Ni-La2O3/CeO2复合镀层在1000°C抗氧化性能的影响。结果表明:与普通Ni镀层相比,Ni-La2O3/CeO2复合镀层中的La2O3/Ce O2颗粒通过溶解扩散进入氧化膜中,阻碍Ni的外扩散,从而降低氧化速度;此外,与La2O3/CeO2纳米颗粒相比,La2O3/Ce O2微米颗粒在氧化初期还起到扩散障碍层的作用,对阻碍Ni的外扩散具有更强的作用。     

Electrocodeposition and characterization of cobalt lanthanide oxides composite coatings

Composite coatings were prepared by electrodeposition of cobalt and the following lanthanide oxides: CeO₂, Nd₂O₃, La₂O₃ and Y₂O₃. The morphology and the particle content of the layers were characterized and their dependence on the deposition parameters is discussed. The highest particle incorporation achieved was 35 wt.% CeO₂ within the cobalt matrix. The amount of incorporated particles (in wt.%) decreased in the order CeO₂ > Y₂O₃ > Nd₂O₃ > La₂O₃. In order to evaluate the improvement of the corrosion resistance of the Cobalt matrix due to the incorporation of lanthanide oxide particles, the electrochemical behaviour of the composite films was studied by linear sweep voltammetry and electrochemical impedance spectroscopy in chloride containing solutions. In comparison with pure Co, Co-Nd₂O₃, Co-La₂O₃ and Co-Y₂O₃ the Co-CeO₂ composite coatings showed a superior corrosion resistance in 0.1 M NaCl.     

Reactive oxide-dispersed Ni3Al intermetallic coatings by sediment co-deposition

Ni–Al-reactive oxide (REO) ternary composite coatings were successfully deposited from a Watt's nickel bath containing Al particles and REO particles via the sediment co-deposition (SCD) technique. Three different composite systems, Ni–Al-nano CeO₂, Ni–Al-5 μm CeO₂, and Ni–Al–Y₂O₃ (<1 μm), were studied. The volume fraction of the Al particles in the composite coatings was significantly decreased with an increase of the REO bath loading, while the REO particle content positively increased. The REO particles in the plating bath evidently interfered with the deposition of Al particles. The development of intermetallic phases in the annealed Ni–Al-REO composite coatings mainly depended on the Al content in the coatings. REO-dispersed Ni₃Al intermetallic coatings could be formed as long as the REO particle loading in the bath was controlled below a critical level. Transformation of CeO₂ phase to CeAlO₃ was found in the Ni–Al-nano CeO₂ composite coatings during the annealing treatment at 800 °C.     

The influence of superficially applied oxide powders on the high-temperature oxidation behavior of Cr2O3-forming alloys

The effects of superficially applied CeO₂, mixed rare earth oxides, Co₃O₄, and Cr₂O₃ powders on the isothermal and cyclic oxidation of Ni-Cr alloys and the effects of CeO₂ and MgO powders on the isothermal oxidation of Fe-25 wt.% Cr have been studied over the temperature range 940–1150°C in pure oxygen and dry air. The rates of oxidation of both the Ni- and Fe-base alloys were markedly reduced by the application of CeO₂ powder. The presence of CeO₂ also improved the scale adherence and resulted in marked changes in the oxidation morphology. The presence of Co₃O₄ or Cr₂O₃ powders on Ni-Cr alloys or MgO on Fe-Cr also produced changes in the oxidation morphology but did not decrease the rate of oxidation. These results are interpreted in terms of the influence of the oxide powders on the development of scale microstructure and their effectiveness in decreasing grain boundary transport in Cr₂O₃.This paper is based in part on the Ph.D. thesis of G. M. Ecer (1975) and in part on the M.S. thesis of R. B. Singh (1977).     

Microstructure and characterization of La2O3 and CeO2 doped diamond-like carbon nanofilms

Seven kinds of hydrogen-free La₂O₃ and CeO₂ doped DLC films with thickness of 220-280 nm were deposited on Si (100) substrates by unbalanced magnetron sputtering. Nanoparticles with diameter of 20-30 nm are formed on the surface of films. The surface roughness Ra of films is in the range of 1.5-2.0 nm. C, La, Ce and O elements distribute uniformly along the depth direction, and C, La, and Ce elements diffuse into the Si substrate at the interface. X-ray photoelectron spectroscopy confirms that the La₂O₃ and CeO₂ form within the DLC amorphous films, and Raman spectra indicate the obvious amorphous characteristics of DLC films. High-resolution transmission electron microscopy shows the nanocrystallines structure with diameter of 2-3 nm of 16% La₂O₃ and 10% CeO₂ doped DLC films, and Fourier transformation spectroscopy also exhibits the obvious crystalline characteristics. In this work, the microstructure of two kinds of rare earth oxides doped DLC composite films is measured and analyzed.