Elastic Properties of Hafnium and Zirconium Oxides Stabilized with Praseodymium or Terbium Oxide

Elastic moduli of polycrystalline HfO₂ and ZrO₂ stabilized with 33 mol% Praseodymium oxide or terbium oxide were studied as functions of porosity and temperature. Thermal expansion was measured to 1200°C for each composition. The modulus-vs-porosity and thermal expansion curves were typical; however, modulus-vs-temperature relations were abnormally steep below 400°C, a phe nomenon observed previously for stabilized HfO₂ compositions. All compositions exhibited obvious stoichiometric changes resulting from oxidation-reduction annealing, but only the Tb₄O₇-stabilized ZrO₂ showed any significant effect of oxidation state on the modulus values; this effect was very pronounced.     

Recent Studies on the Catalytic Activity of Titanium,Zirconium, and Hafnium Oxides

This review article deals with the recent work published on the catalytic activity of transition metal oxides of group IV of the periodic table. These oxides are mainly in the form of MO₂, where M refers to either titanium, zirconium, or hafnium. The preparation of the pure, mixed, and supported oxides, as well as the characterization of their physicochemical properties, are briefly reviewed. However, their catalytic performance in various chemical reactions have been presented in detail. The photocatalytic activity of TiO₂ in many photochemical degradation and conversion processes has been also discussed. Strong emphasis is put on discussion such as the nature and strength of active sites, adsorption of target compounds, kinetic parameters, and reaction mechanisms.     

Recent Studies on the Catalytic Activity of Titanium, Zirconium, and Hafnium Oxides

This review article deals with the recent work published on the catalytic activity of transition metal oxides of group IV of the periodic table. These oxides are mainly in the form of MO₂, where M refers to either titanium, zirconium, or hafnium. The preparation of the pure, mixed, and supported oxides, as well as the characterization of their physicochemical properties, are briefly reviewed. However, their catalytic performance in various chemical reactions have been presented in detail. The photocatalytic activity of TiO₂ in many photochemical degradation and conversion processes has been also discussed. Strong emphasis is put on discussion such as the nature and strength of active sites, adsorption of target compounds, kinetic parameters, and reaction mechanisms.     

锆离子印迹聚合物分离锆和铪的研究

以锆(Ⅳ)离子为印迹离子,磷酸三丁酯(TBP)为络合剂,4-乙烯基吡啶和苯乙烯为功能单体,二乙烯基苯为交联剂,采用本体聚合法制备了锆离子印迹聚合物(Zr-IIPs)和控制聚合物(CPs).用1∶1盐酸将锆离子印迹聚合物中的锆离子洗脱,释放出印迹空腔.对Zr-IIPs和CPs进行了FT-IR和XRD分析表征.研究了pH及...     

Refractory Diborides of Zirconium and Hafnium

This paper reviews the crystal chemistry, synthesis, densification, microstructure, mechanical properties, and oxidation behavior of zirconium diboride (ZrB₂) and hafnium diboride (HfB₂) ceramics. The refractory diborides exhibit partial or complete solid solution with other transition metal diborides, which allows compositional tailoring of properties such as thermal expansion coefficient and hardness. Carbothermal reduction is the typical synthesis route, but reactive processes, solution methods, and pre-ceramic polymers can also be used. Typically, diborides are densified by hot pressing, but recently solid state and liquid phase sintering routes have been developed. Fine-grained ZrB₂ and HfB₂ have strengths of a few hundred MPa, which can increase to over 1 GPa with the addition of SiC. Pure diborides exhibit parabolic oxidation kinetics at temperatures below 1100°C, but B₂O₃ volatility leads to rapid, linear oxidation kinetics above that temperature. The addition of silica scale formers such as SiC or MoSi₂ improves the oxidation behavior above 1100°C. Based on their unique combination of properties, ZrB₂ and HfB₂ ceramics are candidates for use in the extreme environments associated with hypersonic flight, atmospheric re-entry, and rocket propulsion.     

Enhanced Infrared Absorption of C60 on Thin Evaporated Pd Island Films

Infrared transmission spectra of C₆₀ multilayers on thin Pd films deposited onto surface-oxidized Si(100) and hydrogen-terminated Si(111) substrates are reported. In both cases, the spectra in the 1500–1100 cm⁻¹ region exhibited bands at 1444, 1429, and 1182 cm⁻¹ due, respectively, to the A_g (2), T_1u (4), and T_1u (3) modes. The appearance of the A_g (2) mode, which is originally infrared inactive (Raman active), reveals electron transfer from the metal to chemisorbed C₆₀. Indeed, increasing the thickness of C₆₀, the A_g (2) mode intensity saturated more rapidly than the T_1u (4) and T_1u (3) modes. The originally infrared active T_1u (4) and T_1u (3) modes were enhanced in intensity depending upon the Pd thickness. Actually, while both substrates gave nearly the same magnitude of enhancement, the optimum Pd thickness was smaller on the hydrogen-terminated surface than on the surface-oxidized surface. On the other hand, the A_g (2) mode was less intense on the hydrogen-terminated surface than on the oxidized surface, suggestive of a shortage of chemisorbed C₆₀ and thus pointing out the importance of the metal film morphology. Indeed, Pd films deposited on the two substrates gave rise to quite different AFM images. We also show that, regardless of the substrate, the A_g (2) mode is an order of magnitude smaller than for Ag deposition, though no remarkable intensity differences were observed with respect to the T_1u (4) and T_1u (3) modes.     

Formation of Monoclinic Hafnium Titanate Thin Films Via the Sol–Gel Method

Hafnium titanate films are generating increasing interest because of their potential application as high- k dielectrics materials for the semiconductor industry. We have investigated sol–gel processing as an alternative route to obtain hafnium titanate thin films. Hafnia-titania films of different compositions have been synthesized using HfCl₄ and TiCl₄ as precursors. The HfO₂–TiO₂ system composition with 50 mol% of TiO₂ and 50 mol% of HfO₂ has allowed the formation of a hafnium titanate film after annealing at 1000°C. The films exhibited a homogeneous nanocrystalline structure and a monoclinic hafnium titanate phase that has never been obtained before in thin films. The films resulted in the formation of homogeneously distributed nanocrystals with an average size of 50 nm. Different compositions, with higher or lower hafnia contents, produced anatase crystalline films after annealing at 1000°C.     

Production and Optical Characteristics of Films Based on Zirconium, Yttrium, and Iron Oxides

The effect of the composition of film-forming solutions on the optical characteristics of films in the (0.92ZrO₂ ? 0.08Y₂O₃) – Fe₂O₃ system is considered. The kinetics of this process is discussed.     

Thin Films of Cadmium and Dysprosium Oxides as Gas-Sensitive Elements of Sensors

Polycrystalline nanofilms of Dy₂O₃ and CdO are prepared by hydropyrolysis from aqueous solutions of dysprosium and cadmium nitrate salts. The surface morphology of the films and their polycrystalline structure are investigated by X-ray diffraction and electron microscopy. The synthesis of powders is performed by thermolysis of aqueous solutions of cadmium and dysprosium nitrates. The sequence of formation and crystallization of oxide phases of CdO and Dy₂O₃ is ascertained from the X-ray powder diffraction data. The temperature dependence of the electrical resistance of the films obtained is studied in air and argon atmosphere.     

Infrared Properties of Silicon Monox and Evaporated SiO Films

This study is an investigation of the infrared properties of SiO in the wave-length range 1 to 30 μ- The samples used in this study consisted of the commercially available bulk silicon monox and thin films made by evaporating this bulk material. Films which were made by evaporating onto a silicon substrate were used for transmission measurements. Reflectivity measurements as well as transmission measurements were made with the bulk material. From the foregoing data it was concluded that, although the bulk material is not SiO but rather a stoichiometric mixture of Si and SiO₂, the evaporated films are a true amorphous SiO phase.     

Thin-Film Coatings Based on Zirconium and Cobalt Oxides

Thin-film coatings based on zirconium and cobalt oxides are obtained. It is demonstrated that the properties of the coatings depend on the ratio of oxides in the film, the rotational speed of the substrate, and the firing temperature. Films with a low cobalt content have the highest refractive index value and substantial adhesion.     

锆铪萃取分离机理的研究进展

锆和铪的化学性质十分相似,主要通过萃取进行锆铪分离。文章综述不同溶剂萃取分离锆铪的机理:MIBK优先萃取铪、(DIBK)-P204优先萃取铪、TBP优先萃取锆、N235-H2SO4优先萃取锆;以及其他溶剂萃取体系的机理:石油亚砜、Versatic Acid10、Cyanex301、LIX 84-IC等;对工业上得以应用和较为成熟的萃取分离锆铪的体系进行了比较,并讨论了推进产业化的萃取分离锆铪的方向:1新萃取剂的研究;2现有萃取剂改性的研究;3萃取剂消耗量小、萃取时间短的新型萃取技术的研究。     

Magnetic Behavior of Surface Nanostructured 50-nm Nickel Thin Films

Thermally evaporated 50-nm nickel thin films coated on borosilicate glass substrates were nanostructured by excimer laser (0.5 J/cm², single shot), DC electric field (up to 2 kV/cm) and trench-template assisted technique. Nanoparticle arrays (anisotropic growth features) have been observed to form in the direction of electric field for DC electric field treatment case and ruptured thin film (isotropic growth features) growth for excimer laser treatment case. For trench-template assisted technique; nanowires (70–150 nm diameters) have grown along the length of trench template. Coercive field and saturation magnetization are observed to be strongly dependent on nanostructuring techniques.     

Thermal Expansion, Compressibility, and Polymorphism in Hafnium and Zirconium Titanates

Using X-ray diffraction techniques, thermal expansion and compressibility were measured on the orthorhombic compounds HfTiO₄, Hf_1.26Ti_0.74O₄, and ZrTiO₄ (both quenched and cooled slowly from 1300°C). The thermal expansion of HfTiO₄ is highly anisotropic; the thermal expansion coefficients along the crystallographic axes are α _a =+(8.7±0.5)×10⁻⁶°C⁻¹, α _b =−(5.2±0.5)×10⁻⁶°C⁻¹, and α _c =+ (5.3±0.5)×10⁻⁶°C⁻¹. The thermal expansion of Hf_1.26Ti_0.74O₄ was similar to that of HfTiO₄ but that of ZrTiO₄ was markedly less anisotropic. The compressibilities of HfTiO₄ and ZrTiO₄ also differed markedly. All compounds investigated, however, behaved similarly in exhibiting a polymorphic transition to a high-pressure phase having the monoclinic baddeleyite (ZrO₂) structure. The polymorphism can be explained qualitatively on the basis of crystal structure.     

Sol-Gel Preparation of Pb(Zr0.50Ti0.50)O3 Ferroelectric Thin Films Using Zirconium Oxynitrate as the Zirconium Source

Lead zirconium titanate (Pb(Zr_0.5Ti_0.5)O₃, PZT) ferroelectric thin films were successfully deposited on platinum-coated silicon substrates and platinum-coated silicon substrates with a PbTiO₃ interlayer by using a modified sol–gel spin-coating process, using zirconium oxynitrate dihydrate as the zirconium source. The precursor solution for spin coating was prepared from lead acetate trihydrate, zirconium oxynitrate dihydrate, and tetrabutyl titanate. The use of zirconium oxynitrate instead of the widely used zirconium alkoxide provided more stability to the PZT precursor solution and a well-crystallized structure of PZT film at a relatively low processing temperature. PZT films that were annealed at a temperature of 700°C for 2 min via a rapid thermal annealing process formed a well-crystallized perovskite phase of PZT films and also had nanoscale uniformity. The microstructure and morphology of the prepared PZT thin films were investigated via X-ray diffractometry, transmission electron microscopy, and atomic force microscopy techniques. The values for the remnant polarization ( P ) and coercive electric field ( E ) of the PZT films that were obtained from the P–E loop measurements were 3.67 μC/cm² and 54.5 kV/cm, respectively.     

Structures and Polymorphic Transitions of Triacylglycerols, SOS and POS Thin Films: A Study on Temperature Dependence

X-ray reflectivity (XR) and scanning probe microscopy (SPM) were used to examine the structures, polymorphic transitions, and surface morphologies of triacylglycerol (TAG), 1,3-stearin-2-olein (SOS) and 1-palmitin-2-olein-3-stearin (POS) thin films supported on Si substrates. The structural parameters: thickness, electron density, and surface/interface roughnesses of TAG thin films were determined by the nonlinear least-squares regression of XR profiles to reveal their temperature dependences. In the lower temperature regimes, we observed Bragg peaks without significant interference fringe patterns in the XR profiles. SPM at room temperature displayed isolated islands on TAG thin films with surface undulations. Whereas in the higher temperature regimes in which the Bragg peaks disappeared, the interference fringe patterns became prominent. The analyses of the XR profiles indicated the structural change in thin films from three layers to single layer on Si substrates with increasing temperature. However, the temperatures at which the structural change occurred were obviously different between SOS and POS thin films.     

Crystallization Behavior of Sol–Gel-Derived Strontium Barium Niobate Thin Films

The crystallization of sol–gel-derived strontium barium niobate (SBN) thin films on various substrates is enhanced by a two-step heating process. Also, SBN films with c -axis preferred orientation are obtained on MgO (100) substrates. The crystallized phase and the degree of orientation are dependent on crystallization temperature and film composition. The crystallization temperature required to form a single tetragonal tungsten bronze (TTB) SBN phase increases with an increase of Sr content due to the distorted SBN structure. However, in the case of the film on MgO substrate, the oriented crystallization which forms the single tetragonal phase occurs at a lower crystallization temperature than those of polycrystalline films because of lattice matching between the film and the substrate. Its optical and ferroelectric properties were also investigated. They vary depending on film composition, due to the effect of the distorted SBN structure.     

Physical and X-Ray Study of the Disilicides of Titanium, Zirconium, and Hafnium

A method of preparing the disilicides of titanium, zirconium, and hafnium is outlined. Unit-cell dimensions, density, Knoop microhardness numbers, chemical analyses, and solubility in various reagents are given for the three compounds. It is concluded that these disilicides have no value as industrial hard materials.