Synthesis of Lead Nickel Niobate–Lead Zirconate Titanate Solid Solutions by a B-site Precursor Method

A modified processing method for lead nickel niobate–lead zirconate titanate (Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr,Ti)O₃, PNN–PZT) solid solutions is presented. This method is based on the high-temperature synthesis of a precursor that contains all the B-site cations (Ti, Zr, Ni, and Nb). This synthesis yields a diphasic mixture that contains a ZrTiO₄-like phase and a rutile-like phase. Both phases exhibit a cationic valence of 4; thus, it is concluded that the mixing of Ni and Nb cations is adequate for the preparation of PNN–PZT solid solutions. Indeed, a pure perovskite phase has been obtained after calcination with lead oxide for compositions that contain 40 and 50 mol% PNN. Moreover, their electromechanical properties have been shown to be superior to values reported for standard columbite routes. This conclusion has been interpreted in terms of enhanced chemical homogeneity.     

Effect of Bonding Pressure on Silicon Nitride Joining Using a Nickel-Chromium-Boron Metal Filler

Mechanical pressure exerts a noticeable effect on the reaction that takes place at the interfacial region of Si₃N₄/Ni-Cr-B/Si₃N₄ joints. In fact, the mechanical pressure affects the thickness of the reaction layer: for lower pressures, a large interfacial reaction layer and a profusion of cracks are observed, whereas, for higher pressures, the extent of the reaction layer is limited, and no cracks are detected. The results show that joint strength increases monotonically with applied pressure.     

Solid-Solution Effects of a Small Amount of Nickel Oxide Addition on Phase Stability and Mechanical Properties of Yttria-Stabilized Tetragonal Zirconia Polycrystals

Stability and mechanical properties of the tetragonal phase were investigated for NiO-doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) systems. Only 0.3 mol% of NiO in solid solution could be added to the Y-TZP while maintaining the tetragonal phase. Fracture toughness improved remarkably on addition of a small amount of NiO. Raman spectroscopy analysis around cracks introduced by Vickers indentation revealed that the amount of monoclinic phase transformed from tetragonal phase was increased. It was confirmed that fracture toughness improvement was due not only to increased grain size, but also to Y-TZP destabilization by solid solution of NiO.     

Formation of High-Quality, Epitaxial La2Zr2O7 Layers on Biaxially Textured Substrates by Slot-Die Coating of Chemical Solution Precursors

Crystallization studies were performed of epitaxial La₂Zr₂O₇ (LZO) films on biaxially textured Ni–3at.%W substrates having thin Y₂O₃ (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c -axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850°–950°C in flowing one atmosphere gas mixtures of Ar–4% H₂ with an effective oxygen partial pressure of P(O₂)∼10⁻²² atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100°C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures.     

高分子辅助沉积法在镍基片上制备的钛酸钡薄膜的漏电机制

采用高分子辅助沉积法在多晶镍衬底上,以氧化镍作为缓冲层,生长了多晶钛酸钡(BaTiO3,BTO)薄膜。对其漏电特性测试及分析发现,在测试电压区间和极性不同时,分别具有不同的漏电机制,可分别用Frankel-Pool emission,space charge limited current(SCLC)与Schottky emission等机制来描述。由于界面缓冲层分解以及界面扩散等原因,BTO/Ni界面呈现Ohmic接触,而Au/BTO界面呈现Schottky势垒接触。通过测量不同温度下的漏电流大小,得到Au/BTO界面的有效势垒为0.32eV,从而得到Au/BTO/Ni能带结构图。利用一阶线性电路模型对其界面电阻与体电阻进行计算,得到的界面电阻与体电阻大小及变化趋势与实验及理论相符合。     

Fabrication of Lanthanum Manganese Oxide Thin Films on Yttria-Stabilized Zirconia Substrates by a Chemically Modified Alkoxide Method

Perovskite-type thin films of lanthanum manganese oxide (LaMnO₃) were prepared on yttria (8%) stabilized zirconia substrate by the sol–gel process from an alkoxide solution of lanthanum isopropoxide (La(O- i -C₃H₇)₃) and manganese isopropoxide (Mn(O- i -C₃H₇)₂). The alkoxide solution was chelated with 2-ethyacetoacetate, and further modified with polyethylene glycol (PEG). The obtained LaMnO₃ thin film was transparent and macroscopically crackless. X-ray diffraction, differential thermal analysis–thermogravimetry analysis, and scanning electron microscope observations indicated that single-phase LaMnO₃ thin films with a grain size of 80 to 100 nm are formed when a spin-coated LaMnO₃ gelled film is heated at 600°C for 1 h. The porous and homogeneous grain structure with a grain size of <100 nm can be obtained when the LaMnO₃ gelled film is heated at 600° and 800°C. It was considered that PEG might accelerate the crystallization of the perovskite phase, which indicates that PEG assists the formation of the La-O-Mn frame network during partial hydrolysis and condensation reactions in sol–gel processes.     

Effect of Processing Parameters on Physical Properties of Cadmium Stannate Thin Films Prepared by a Dip-Coating Technique

Thin films of dicadmium stannate spinel (Cd₂SnO₄) were deposited on glass substrates using a dip-coating technique. The films were transparent to visible light (90%) and electrically conductive. X-ray diffractometry showed that annealed films consisted of a single cubic spinel phase only when they were prepared from a solution with the composition of Cd:Sn = 2.5 and fired at a temperature of 400°–500°C. The Cd:Sn ratio, the firing temperature, and the post-deposition annealing sequence were crucial for the formation of a single phase, which is vital to obtain optimal optical and electrical properties. A resistivity as low as 3.3 × 10⁻⁴Ω·cm could be obtained after annealing.     

Synthesis and Characterization of NiO Nano‐Spheres by Templating on Chitosan as a Green Precursor

In this study, nickel oxide was prepared through the calcination of extrusion dripped chitosan/nickel nitrate beads. The morphology and structural properties of the products were studied using various characterization techniques. Uniformly distributed nickel oxide was formed as observed from the studies of surface morphology where the processing parameters play a huge role on the resulting morphology. TEM results have shown that nickel oxide with crystallite sizes of 10–30 nm was obtained. The Fourier‐transform infrared spectra studies show an intense peak at 525 cm^?1, which is attributed to the vibration of Ni–O bond. Furthermore, the XRD results show NiO diffraction peaks correspond to (111), (200), (220), (311), and (222) which indicates that a bunsenite structure with a face‐centered cubic phase was produced in this study. The usage of 500°C as the lower limit in this study is justified due to the complete removal of the templating material as seen in the thermalgravimetric analysis studies. Furthermore, it was obtained that the largest surface area of nickel oxide synthesized using this technique is 48.024 m²/g with pore sizes of 19.843 nm. The usage of chitosan as a green template for the synthesis of nanoparticles has shown promising results which allows a more economical and sustainable approach for the fabrication of nanomaterials.     

Thermal Stability of a Chemically Vapor Deposited Multilayer Coating Containing Amorphous Silica and Rutile Titania on Hi-Nicalon Fiber

A multilayer coating consisting of consecutive layers of amorphous-silica, rutile-titania, and amorphous-silica was prepared on Hi-Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h.