Dependence of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coating thickness and annealing conditions on microstructural and electrochemical properties of LiCoO<Subscript>2</Subscript> film

We studied the dependence of Al₂O₃ coating thickness and annealing conditions on the surface morphology and electrochemical properties of Al₂O₃ coated LiCoO₂ films. The optimum coating thickness allowing for the highest capacity retention was about 24 nm. A sample consisting of Al₂O₃ coated on annealed LiCoO₂ film with additional annealing at 400 °C had a uniform coating layer between the coating materials and cathode films. This sample showed the best capacity retention of ∼91 % with a charge-cut off of 4.5 V after 30 cycles, while the bare cathode film showed a capacity retention of ∼32 % under the same conditions. The formation of second phases such as Co-Al-O was observed in the coating films by X-ray photoelectron spectroscopy (XPS). The Co-Al-O containing samples showed a higher initial capacity because of their smaller grain size, but less capacity retention than the Al₂O₃ containing samples.     

非晶态SrTiO3薄膜的快速晶化处理

在Si(111)基片上采用脉冲激光沉积(PLD)方法,烘烤温度300℃,制备得到非晶态SrTiO3薄膜.采用快速晶化处理,将非晶态SrTiO3薄膜在不同温度、不同晶化处理时间下进行了晶化处理,采用GIXRD和AFM分析检验晶化的效果和表面形貌.结果表明,SrTiO3晶化程度强烈依赖处理温度,处理温度越高,晶化程度越高;在同一温度下,增加处理时间有助于提高晶化效果,并获得致密、表面平整、均匀的SrTiO3晶态薄膜;晶粒大小不随晶化处理时间明显变化.在快速晶化处理过程中,非晶态SrTiO3薄膜在极短时间内达到晶化温度,并形成大量晶核,从而使晶粒生长受到限制,有利于获得更好的晶化效果.     

Resistance switching of heteroepitaxial Cr-doped SrZrO<Subscript>3</Subscript> thin films

Heteroepitaxial Cr-doped SrZrO₃ thin films were grown on 200 nm-thick SrRuO₃ films deposited on SrTiO₃ (100) substrates by pulsed laser deposition. The Cr-doped SrZrO₃ films on the SrRuO₃ bottom electrode exhibited an XRD peak for the (hh0/00l) planes of SrZrO₃ and SrRuO₃ thin films, showing a good epitaxial relationship. The I–V characteristics of the Au/Cr-doped SrZrO₃/SrRuO₃ MIM structures revealed resistance switching behavior with an ON/OFF resistance ratio of 20.     

Corrosion behaviour of polycrystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films and its size effects

This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb₂O₅ thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb₂O₅ and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb₂O₅ improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.     

Preparation of ZrO<Subscript>2</Subscript> dielectric layers by subsequent oxidation after Zr film deposition with negative substrate bias voltage

ZrO₂ dielectric layers were prepared by a two-step process, a deposition of pure Zr film with and without a negative substrate bias voltage and a subsequent oxidation of the Zr films. We focused on the effect of the negative substrate bias voltage on the Zr film deposition and the subsequent oxidation of the Zr films. As a result, the Zr film deposited at the substrate bias voltage of −50 V (Vs = −50 V) was found to have a high intensity peak of Zr (100) and a uniform and smooth surface. From the capacitance-voltage and current-voltage measurements of the ZrO₂ films, a high dielectric constant of 21 and the equivalent oxide thickness (EOT) of 2.6 nm were obtained on the oxidation layer of the Zr film deposited at Vs = −50 V. On the other hand, a low dielectric constant of 15 and the EOT of 3.6 nm was obtained on that of the Zr film deposited at Vs = 0 V. The leakage current density of the ZrO₂ film (Vs = −50 V) was 5.69×10⁻⁴ A/cm², and this value was much lower than the 1.21×10⁻⁴ A/cm² for the ZrO₂ film (Vs = 0 V). It was found that the two-step process by subsequent oxidation after film deposition using a negative substrate bias voltage is useful for obtaining high-quality dielectric layers.     

Multiferroic BiFeO<Subscript>3</Subscript> thick film fabrication by aerosol deposition

BiFeO₃ (BFO) multiferroic materials in the crystalline phase require very delicate processing conditions. In order to fabricate a high quality BFO thick film, aerosol deposition (AD) was employed and the phase evolution and multiferroic properties of the film were investigated for different annealing temperatures. A BFO thick film annealed at 500 °C had a dielectric constant of 80 at 1 kHz and possessed ferroelectric characteristics. At an applied electric field of ∼900 kV/cm, the remaining polarization and coercive field (E_c) were approximately 7.5 μC/cm² and 370 kV/cm, respectively. In addition, the BFO thick film fabricated via AD and annealed at 500 °C showed weak ferromagnetic behavior between −1250 Oe and +1250 Oe and was saturated at the higher magnetic field strength, showing ferromagnetic behavior.     

Obtaining ZrO<Subscript>2</Subscript> + CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> + TiO<Subscript>2</Subscript>/Ti compositions by plasma-electrolytic oxidation of titanium and investigating their properties

Regularities of the effect produced by Ce₂(SO₄)₃ salt introduced in an aqueous electrolyte containing Zr(SO₄)₂ on the plasma-electrolytic formation of oxide coatings on titanium, their composition, and structure are studied. ZrO₂ + CeO _x + TiO₂ three-phase oxide coatings with a thickness about 10 μm are obtained. The coatings involve ZrO₂ cubic phase. The ZrO₂-to-TiO₂ phase ratio in the coatings can be controlled. The zirconium content in the coatings reaches 20 at %, while that of cerium is 3–5 at %. The surface layer (∼3-nm thick) contains Ce³⁺ (∼30%) and Ce⁴⁺ (∼70%). Pores in the surface part of coatings have diameters around or smaller than 1 μm and are regularly arranged. The obtained systems have a certain catalytic activity with respect to the oxidation of CO to CO₂ at temperatures above 400–450°C. The coatings are corrosion-resistant in chloride-containing environments. The thickness h of coatings depending on the charge Q supplied to the cell is described by the equation h = h ₀(Q/Q ₀) ⁿ , where n = 0.35 and h ₀ is the thickness of the coating formed at Q ₀ = 1 C/cm².     

HVOF thermal spray deposited Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-stabilized ZrO<Subscript>2</Subscript> coatings for thermal barrier applications

High velocity oxy-fuel (HVOF) thermal spray has been successfully used to deposit yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications. Adherent coatings were obtained within a limited range of spray conditions using hydrogen as fuel gas. Spray parameters such as hydrogen-to-oxygen ratio, spray distance, and substrate cooling were investigated. Spray distance was found to have a pronounced effect on coating quality; adherent coatings were obtained for spray distances between 75 and 125 mm from the gun exit for the hydrogen-to-oxygen ratios explored. Compared to air plasma spray (APS) deposited YSZ coatings, the HVOF deposited coatings were more fully stabilized in the tetragonal phase, and of similar density, surface roughness, and cross-sectional microhardness. Notably, fracture surfaces of the HVOF coatings revealed a more homogeneous structure. Many theoretical models predict that it should not be possible to melt YSZ in an HVOF flame, and therefore it should not be possible to deposit viable YSZ coatings by this process. The experimental results in the present work clearly contradict those expectations. The present results can be explained by taking into account the effect of partial melting and sintering on particle cohesion, as follows. Combustion chamber pressures (P _o) of ∼3.9 bar (58.8 psi) realized during HVOF gun operation allows adiabatic flame temperature values that are above the zirconia melting temperature. Under these conditions, the Ranz-Marshall heat transfer model predicts HVOF sprayed particle surface temperatures T _p that are high enough for partial melting of small (∼10 μm) zirconia particles, T _p=(1.10−0.95)T _m. Further analysis shows that for larger particles (38 μm), adherent coatings are produced when the particle temperature, T _p=0.59−0.60 T _m, suggesting that sintering may have a role in zirconia particle deposition during HVOF spray. These results suggest two different bonding mechanisms for powders having a broad particle size distribution.     

The role of Ce ions in electrochemical corrosion of 304 SS in Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>.6H<Subscript>2</Subscript>O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO₃]₃.6H₂O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 V_SCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 V_SCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO₃ ⁻) ions in Ce(NO₃)₃.6H₂O electrolyte.     

Epitaxial integration of perovskite-based multifunctional oxides on silicon

We review recent developments in the epitaxial integration of multifunctional oxide thin film heterostructures on silicon (Si). Perovskite oxides have been extensively studied for use in multifunctional devices due to a wide range of functional properties. To realize multifunctional oxide devices, these multifunctional films should be integrated directly on Si, maintaining high crystalline quality. Molecular beam epitaxy growth of epitaxial SrTiO₃ (STO) on Si provides a template for incorporating the epitaxial oxide films on Si. However, the dissimilar physical nature of Si from most oxide materials influences the properties of oxide films on Si, especially with regard to structural defects and thermal strains. Therefore, in this review, we present a comprehensive overview of epitaxial integration of various model oxide systems on Si, addressing how STO/Si can be used to explore the novel phenomenon of oxide heterostructures as well as to realize multifunctional devices.     

Comparative analysis of the kinetics of dissolution of oxides Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in the iron matrix upon mechanical alloying

The kinetics of low-temperature dissolution of oxides Y₂O₃ and Fe₂O₃ in an iron matrix during mechanical alloying has been studied using electron microscopy. It has been shown that the dissolution rate upon deformation of primary coarse oxides Fe₂O₃ in α iron (and, hence, saturation of the α matrix with oxygen) during treatment in a ball mill for up to 10 h is several times higher than the dissolution rate of Y₂O₃ oxides. The high-temperature (1100°C) annealing of a mechanoalloyed mixture of Fe + 1.5% Y + 1.35% Fe₂O₃ leads to the precipitation of 60% (of the total number of particles) secondary oxides 2–5 nm in size and only of 5–7% secondary nanooxides in a mechanoalloyed mixture of Fe + 2% Y₂O₃.     

Room temperature ferroelectric property of BiMnO<Subscript>3</Subscript> thin film with double SrTiO<Subscript>3</Subscript> buffer layers on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrate

We fabricated high quality BiMnO₃ thin films with double SrTiO₃ buffer layers on Pt/Ti/SiO₂/Si substrates, in which the SrTiO₃ buffer layers were used for the reduction of leakage current in BiMnO₃ thin films. We chose an SrTiO₃ thickness of about 5 nm, which was obtained by the fitting of ellipsometer data. We confirmed a remarkable enhancement in leakage current. BiMnO₃ thin films exhibited a ferromagnetic transition with Curie temperature of about 105 K. The BiMnO₃ thin film also showed a good ferroelectric property with a remnant polarization of about 9 μC/cm².     

Irradiation-induced order-to-disorder phase transformation at different temperatures in Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>

Polycrystalline pellets of the rare earth sesquioxide Dy₂O₃ were irradiated at two temperatures (∼120 K and ∼300 K) with 300 keV Kr⁺⁺ ions up to a fluence of 1 × 10²⁰ Kr/m². The crystal structure of the irradiated Dy₂O₃ was observed to change from an ordered cubic bixbyite structure (so-called C-type rare earth sesquioxide structure) to a disordered, anion-deficient fluorite structure. A relatively low ion dose (∼2.5 displacements per atom [dpa]) was sufficient to induce a complete order-to-disorder (O-D) phase transformation at cryogenic temperature (∼120 K) irradiation, while at room temperature (∼300 K) a higher dose (∼25 dpa) produced only a partial O-D phase transformation. Dr. Tang can be reached at Mail-Stop G755.     

Flame-Sprayed Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Films with Metal-EDTA Complex Using Various Cooling Agents

In this study, yttrium oxide (Y₂O₃) films were synthesized from a metal-ethylenediaminetetraacetic (metal-EDTA) complex by employing a H₂-O₂ combustion flame. A rotation apparatus and various cooling agents (compressed air, liquid nitrogen, and atomized purified water) were used during the synthesis to control the thermal history during film deposition. An EDTA·Y·H complex was prepared and used as the staring material for the synthesis of Y₂O₃ films with a flame-spraying apparatus. Although thermally extreme environments were employed during the synthesis, all of the obtained Y₂O₃ films showed only a few cracks and minor peeling in their microstructures. For instance, the Y₂O₃ film synthesized using the rotation apparatus with water atomization units exhibited a porosity of 22.8%. The maximum film’s temperature after deposition was 453 °C owing to the high heat of evaporation of water. Cooling effects of substrate by various cooling units for solidification was dominated to heat of vaporization, not to unit’s temperatures.     

Dielectric properties of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films deposited onto Ti and TiO<Subscript>2</Subscript> layer

The present study describes the dielectric properties of RF sputtered Ta₂O₅ thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO₂. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta₂O₅ thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta₂O₅ fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta₂O₅/Ti/Si/Cu and Cu/Ta₂O₅/TiO₂/Si/Cu) indicated that the amorphous Ta₂O₅ grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10⁻¹–10⁻⁴ A/cm²), whereas a relatively low dielectric constant (−10) and low leakage current (−10⁻¹⁰ A/cm²) were observed in the amorphous Ta₂O₅ deposited on the TiO₂ buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta₂O₅ thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta₂O₅/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta₂O₅/TiO₂ film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.     

Cr doping effect in B-site of La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> on its phase stability and performance as an SOFC anode

La_0.75Sr_0.25Cr _y Mn_1−y O₃ (LSCM) (y = 0.0–0.6) composite oxides were synthesized by a complexing process of combining ethylene diamine tetraacetic acid (EDTA) and citrate. X-ray diffraction (XRD), temperature-programmed reduction, electrical conductivity, I–V polarization, and impedance spectroscopy were conducted to investigate the Cr doping effect of La_0.75Sr_0.25MnO₃ on its phase stability and electrochemical performance as a solid-oxide fuel cell (SOFC) anode. The chemical and structural stabilities of the oxides increased steadily with increasing Cr doping concentration, while the electrical conductivity decreased on the contrary. At y ≥ 0.4, the basic perovskite structure under the anode operating condition was sustained. a cell with 0.5-mm-thick scandia-stabilized zirconia electrolyte and La_0.75Sr_0.25Cr _y Mn_1−y O₃ anode delivered a power density of ∼15 mW·cm⁻² at 850°C.     

RETRACTED ARTICLE: Dislocation-particle interaction in precipitation strengthened Ll<Subscript>2</Subscript>-ordered Ni<Subscript>3</Subscript>Al

Transmission electron microscope investigation has been performed on the particle-dislocation interactions in Ni₃Al-based intermetallics containing various types of fine precipitates. In an Ll₂-ordered Ni₃Al alloy with 4 mol.% of chromium and 0.2–0.5 mol.% of carbon, fine octahedral precipitates of M₂₃C₆ type carbide, which has a cube-cube orientation relationship with the matrix, appear during aging. Typical Orowan loops are formed in Ni₃Al containing fine dispersions of M₂₃C₆ particles. In the alloys with appropriate titanium content, fine precipitates of coherent disordered γ are formed during aging. The γ precipitates are initially spherical or rounded cubic in shape and grow into platelets as aging proceeds. Loss of coherency is initiated by the introduction of dislocations at the γ/γ′ interface and results in step formation at the dislocations. The γ precipitates become globular after the loss of coherency. In the γ′ phase hardened by the precipitation of the disordered γ phase, dislocations are attracted into the disordered γ phase and cut through the particles during deformation at any stage of aging. In Ni₃Al containing a fine dispersion of disordered γ, superdislocations are strongly attracted to the disordered particles and dissociate on the (111) plane in the γ particles, while they dissociate on the (010) plane in the matrix. It is shown by comparison that the strengthening due to attractive interaction is more effective than that due to repulsive interaction. The roles of the variation of the interaction modes and of the dissociation of superdislocations in the matrix and particles are discussed in connection with the optimum microstructures of Ll₂-ordered intermetallics as high temperature structural materials.     

织构金属衬底上CSD-SrTiO3薄膜的制备

涂层导体是发展77 K液氮温区强磁场下电力应用的实用化关键材料。由于缓冲层层数增加会导致控制生长、微观组织和界面结构的难度增大,所以简化缓冲层结构对涂层导体制备工艺的简化和成本的降低非常重要。本研究探索了低成本的化学溶液沉积(CSD)技术制备SrTiO_3(STO)缓冲层过程中前驱液热分解行为以及薄膜制备工艺路线对薄膜外延生长的影响,通过选取恰当的前驱液以及引入籽晶层沉积的方法最终获得了具有良好c轴织构且表面光滑的STO薄膜。     

Crystallization behaviour and high coercivity of （Nd,Pr）（13）Fe（80）Nb1B6 melt-spun ribbons

Amorphous (Nd,Pr)₁₃Fe₈₀Nb₁B₆ ribbons were crystallized at 670–730°C for 5–25 min to study the effects of isothermal crystallization on their behavior and magnetic properties. XRD results indicate that the isothermal incubation time is 12, 5, and less than 5 min at 670, 700, and 730°C, respectively. High coercivities, with the maximum value of _i H _c = 1616 kA/m at 700°C for 19 min, measured by a physical property measurement system, are obtained in the crystallized ribbons. This is mainly attributed to the addition of Pr and Nb, because Pr₂Fe₁₄B has a higher anisotropic field than Nd₂Fe₁₄B, and Nb enriched in the grain boundary regions can not only reduce the exchange-coupling effects among hard grains, but also impede grain growth during the crystallization process. In addition, it should also be related to the characteristics of the furnace that the authors designed.     

Structural changes during the reaction of Ni thin films with (1 0 0) silicon substrates

Ultrathin films of nickel deposited onto (1 0 0) Si substrates were found to form kinetically constrained multilayered interface structures characterized by structural and compositional gradients. The presence of a native SiO₂ on the substrate surface in tandem with thickness-dependent intrinsic stress of the metal film limits the solid-state reaction between Ni and Si. A roughly 6.5 nm thick Ni film on top of the native oxide was observed regardless of the initial nominal film thickness of either 5 or 15 nm. The thickness of the silicide layer that formed by Ni diffusion into the Si substrate, however, scales with the nominal film thickness. Cross-sectional in situ annealing experiments in the transmission electron microscope elucidate the kinetics of interface transformation towards thermodynamic equilibrium. Two competing mechanisms are active during thermal annealing: thermally activated diffusion of Ni through the native oxide layer and subsequent transformation of the observed compositional gradient into a thick reaction layer of NiSi₂ with an epitaxial orientation relationship to the Si substrate; and, secondly, metal film dispersion and subsequent formation of faceted Ni islands on top of the native oxide layer.