Effects of some rare earth oxides and/or SiO2 additions to a commercial ZrO2 paint for coating SiGe thermoelectric materials

The effects of some rare earth oxides (Y₂O₃, CeO₂, Sm₂O₃ or Er₂O₃) and/or SiO₂ additions to a commercial oxide paint (mainly ZrO₂) were studied as coatings for SiGe thermoelectric materials. No spalling occurred in the samples prepared from coatings containing small amounts of Er₂O₃, SiO₂ or both CeO₂ and SiO₂ while heating for 1322 h at 1080° C in vacuum, and the sublimation of silicon and/or germanium was reduced significantly. The improvements imparted by these oxide additions to the commercial oxide paint is thought to be due to decreased internal stress of the surface oxides. The addition of Y₂O₃ and Sm₂O₃ had a detrimental effect.     

Effect of erbium on varistor characteristics of vanadium oxide-doped zinc oxide ceramics

The effect of erbium addition on microstructure, electrical properties, and ageing behavior of vanadium oxide-doped zinc oxide varistor ceramics was systematically investigated. Analysis of the microstructure indicated that the ceramics added with erbium consisted of ZnO grain as a main phase and secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, ErVO₄, V₂O₅, and Mn-rich. The average grain size decreased from 5.5 to 5.2 μm up to 0.05 mol%, whereas a further addition gradually increased it to 5.7 μm at 0.25 mol%. The sintered density increased from 5.51 to 5.61 g/cm³ with an increase in the amount of Er₂O₃. With increasing the amount of Er₂O₃, the breakdown field increased from 4,800 to 5,444 V/cm up to 0.05 mol%, whereas a further addition decreased it to 4,061 V/cm at 0.25 mol%. The varistor ceramics added with 0.05 mol% Er₂O₃ additives induced excellent nonlinear properties, with nonlinear coefficient of 63.4 by properly adding the amount of Er₂O₃ (0.05 mol%). The study indicated that the erbium acted as a donor to increase the donor concentration with an increase in the amount of Er₂O₃.     

The morphology of alumina scales formed on Fe-20Cr-4Al-S alloys with reactive element (Y,Hf) additions at 1273 K

Abstract

The morphology of alumina scales formed on Fe–20Cr–4Al–S (185 ppm) alloys with reactive elements (10, 300, 800, and 3700 ppmY, 500, 900, 1900, and 4300 ppmHf) was studied in oxidizing atmospheres at 1273 K for 18, 1800 and 3600 ks by mass gain measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). No spalling of the oxide scales was observed on any of the alloys after any of the oxidation times. Mass gain decreased for alloys with small additions of reactive elements, and then increased with increasing reactive element content. Oxide scales on the 185 ppmS, the 500 and 900 ppmHf alloys showed a wavy morphology. On the other hand, oxide scales on the other alloys with reactive elements changed from small wavy to planar morphologies with increasing reactive elements after any of the oxidation times studied. Oxide scales formed on all of the alloys were recognized as mainly _-Al₂O₃. After oxidation for 3600 ks, Y₃Al₅O₁₂ particles were observed for the 800 and the 3700 ppmY alloys, and HfO₂ particles were also detected for the 1900 and the 4300 ppmHf alloys.     

Elastic properties of partially-stabilized HfO2 compositions

The effect of metastable tetragonal HfO₂ on the elastic properties of partially stabilized HfO₂ doped with Er₂O₃, Y₂O₃ or Eu₂O₃ was studied using a sonic resonance technique. The elastic moduli were monitored at elevated temperatures to follow the effect of the tetragonal-monoclinic phase transformation. Elastic moduli were also determined as a function of porosity and found to follow linear relations. The non-linear modulus versus temperature relations from room temperature to 500° C are explained in terms of the oxygen vacancies present in the fluorite type phase.     

Influences of Er3+ content on structure and upconversion emission of oxyfluoride glass ceramics containing CaF2 nanocrystals

Transparent 45SiO₂–25Al₂O₃–5CaO–10NaF–15CaF₂ glass ceramics doped with different content of erbium ion (Er³⁺) were prepared. X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses evidenced the spherical CaF₂ nanocrystals homogeneously embedded among the glassy matrix. With increasing of Er³⁺ content, the size of CaF₂ nanocrystals decreased while the number density increased. The crystallization kinetics studies revealed that CaF₂ crystallization was a diffusion-controlled growth process from small dimensions with decreasing nucleation rate. Er³⁺ could act as nucleating agent to lower down crystallization temperature, while some of them may stay at the crystal surfaces to retard the growth of crystal. Intense red and weak green upconversion emissions were recorded for glass ceramics and their intensities increased with the increasing of Er³⁺ content under 980 nm excitation. However, the concentration quenching effect appeared when Er³⁺ doping reached 2 mol%. These results could be attributed to the change of ligand field of Er³⁺ ions due to the incorporation of Er³⁺ ions into precipitated fluoride nanocrystals.     

Spectroscopic ellipsometry and positron annihilation investigation of sputtered HfO2 films

Hafnium oxide (HfO₂) films were prepared using a pulsed sputtering method and different O₂/(O₂ + Ar) ratios, deposition pressures, and sputtering powers. Spectroscopic ellipsometry (SE) and positron annihilation spectroscopy (PAS) were used to investigate the influence of the deposition parameters on the number of open volume defects (OVDs) in the HfO₂ films. The results reveal that a low O₂/(O₂ + Ar) ratio is critical for obtaining films with a dense structure and low OVDs. The film density increased and OVDs decreased when the deposition pressure was increased. The film deposited at high sputtering power showed a denser structure and lower OVDs. Our results suggest that SE and PAS are effective techniques for studying the optical properties of and defects in HfO₂ and provide an insight into the fabrication of high-quality HfO₂ thin films for optical applications.     

Effects of rare earth additions during surface boriding on microstructure and properties of titanium alloy TC21

Abstract

In the present paper, the effects of rare earth (RE) additions to the solid state boriding of titanium alloy TC21 have been studied. The microstructural evolution and phase transformations of the borided layers were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction. Moreover, the microhardness for the borided layer was also determined by Vickers hardness test. The results showed that the addition of a small amount of RE elements in the boriding process can lead to an increased boron concentration in the surface layer coupled with the improved surface hardness and coating layer thickness. Furthermore, the presence of trace quantities of RE oxide (Ce₂O₃) in boride layers indicated that the RE elements as catalysts could not only influence but also accelerate boriding process.     

High-temperature behavior of oxide dispersion strengthening CoNiCrAlY

Abstract

To fabricate oxide dispersion strengthened bond coatings, commercial Co–30wt-%Ni–20Cr–8Al–0?4Y powder was milled with 2% additions of Al₂O₃, Y₂O₃ or Y₂O₃ + HfO₂. Low-pressure plasma sprayed, free-standing specimens were oxidised in air + 10%H2O at 1100 °C both isothermally (100 h) and in 500, 1?h cycles. Dry air cyclic testing conducted at both ORNL and FZJ showed remarkably similar results. In general, the water vapour addition caused more scale spallation. Two LPPS specimens without oxide additions were tested for comparison. The specimens with 2%Al₂O₃ addition exhibited the best behaviour as the powder already contained 0?4%Y. Additions of 2%Y₂O₃ and especially 1%Y₂O₃ + 1%HfO₂ resulted in over-doping as evidenced by high mass gains and the formation of Y- and Hf-rich pegs. Scanning transmission electron microscopy of the isothermal specimens showed no Hf and/or Y segregation to the alumina scale grain boundaries in the over-doped specimens.     

Preparation and photoluminescence of Er-doped Al2O3 films by sol-gel method

The 0-1.5 mol% Er³⁺-doped Al₂O₃ films have been prepared on the thermally oxidized SiO₂/Si(100) substrate in the dip-coating process by the sol-gel method, using the aluminium isopropoxide [Al(OC₃H₇)₃]-derived γ-AlOOH sols with the addition of erbium nitrate [Er(NO₃)₃·5H₂O]. The continuous Er³⁺-doped Al₂O₃ films with the thickness of about 1.2 μm were obtained for nine coating cycles at a sintering temperature of 900 °C. The aggregate size for the Er³⁺-doped Al₂O₃ films increased with increasing the Er³⁺ doping concentration from 0 to 1.5 mol%. The root-mean-square roughness of the films was independent on the Er³⁺ doping, which was about 1.8 nm for the 0-1.5 mol% Er³⁺-doped Al₂O₃ films. The γ-Al₂O₃ phase with a (110) preferred orientation was produced for the Al₂O₃ film. The photoluminescence (PL) spectra of 0.1-1.5 mol% Er³⁺-doped Al₂O₃ films were observed at the measurement temperature of 10 K. There was no significant change for the PL peak intensity with the increase of Er³⁺ doping concentration from 0.1 to 1.5 mol%, and similar full width at half maximum of about 40 nm was detected for the 0.1-1.5 mol% Er³⁺-doped Al₂O₃ thin films. The Er³⁺-doped Al₂O₃ films possess the available PL properties for use in planar optical waveguides.     

Dependence of thermo-mechanical and mechanical properties of novel fluorophosphate glass on various rare earth dopants

The dependence of thermo-mechanical, and mechanical properties on various rare earth dopants (RE) including Nd₂O₃, Er₂O₃, and Yb₂O₃ in 0.4MgF₂-0.4BaF₂-0.1Ba(PO₃)₂-0.1Al(PO₃)₃ glasses (MBBA system) is systematically investigated. MBBA system doped with RE dopants presented the potential application in the field of communication and high power layer system in the previous reports. In this work, it is found that the density of the doped glass increases with an increasing of RE concentration, which could be understood in terms of cationic field strength (CFS) effect. The Knoop hardness is found to decrease with the loading time and dopant concentration due to the indentation size effect (ISE) effect. The observed decrease of thermal expansion coefficient and the increase of glass transition temperature T _g with increasing dopant concentration are elucidated in terms of the increasing number of strong covalent bonds with increasing RE dopant concentration. Those results will be of paramount importance before designing optical devices.     

The effects of O2/Ar ratio on the structure and properties of hafnium dioxide (HfO2) films

HfO₂ films at various O₂/Ar flow ratios were prepared by reactive dc magnetron sputtering. The effects of O₂/Ar ratio on the structure and properties of HfO₂ films were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV-Visible spectroscopy. The results showed that the HfO₂ films were amorphous at different O₂/Ar ratios, and the atomic ratio of O/Hf in the HfO₂ films at high O₂/Ar ratio was nearly to 2:1. The peaks of Hf4f and O1s shifted to higher binding energy with increasing the oxygen flow proportion. The HfO₂ films at high O₂/Ar ratio had high transmissivity at the range of 400-1100 nm.     

Infrared Luminescence of Y2O2S:Er3+ and Y2O3:Er3+

The diffuse reflectance and luminescence spectra of Y₂O₂S:Er³⁺ and Y₂O₃:Er³⁺ are studied under selective and polarized laser excitation. The results indicate that the Er³⁺ luminescence bands of yttrium oxysulfide in the 1.54-m region are one order of magnitude stronger and broader than those of yttria. Y₂O₂S:Er³⁺ is shown to contain two types of Er-related emission centers differing in the anion environment of the Er³⁺ ion.     

Laser raman spectroscopic studies of the surface oxides formed on iron chromium alloys at elevated temperatures

Binary iron-base alloys containing chromium additions of 3, 9, 12 and 18 % were oxidized in air at elevated temperatures. Laser Raman spectroscopy has been used to determine the chemical compounds of the oxides of these alloys. It is found that the oxides formed on Fe-3Cr alloy at various elevated temperatures consist mainly of iron. However, for Cr additions ≥12 %, the surface oxide formed at 400°C consists of αFe₂O₃, Fe₃O₄ and spinel phases. With increasing oxidation temperature up to 850°C, the oxide scale consists of Cr₂O₃ and spinel phases only.     

Atomic layer deposition grown composite dielectric oxides and ZnO for transparent electronic applications

In this paper, we report on transparent transistor obtained using laminar structure of two high-k dielectric oxides (hafnium dioxide, HfO₂ and aluminum oxide, Al₂O₃) and zinc oxide (ZnO) layer grown at low temperature (60 °C-100 °C) using Atomic Layer Deposition (ALD) technology. Our research was focused on the optimization of technological parameters for composite layers Al₂O₃/HfO₂/Al₂O₃ for thin film transistor structures with ZnO as a channel and a gate layer. We elaborate on the ALD growth of these oxides, finding that the 100 nm thick layers of HfO₂ and Al₂O₃ exhibit fine surface flatness and required amorphous microstructure. Growth parameters are optimized for the monolayer growth mode and maximum smoothness required for gating.     

Effect of atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers on the performance of dye sensitized solar cells

The objective of this work was to investigate the improvement in performance of dye sensitized solar cells (DSSCs) by depositing ultra thin metal oxides (hafnium oxide (HfO₂) and aluminum oxide (Al₂O₃)) on mesoporous TiO₂ photoelectrode using atomic layer deposition (ALD) method. Different thicknesses of HfO₂ and Al₂O₃ layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO₂ surface prior to dye loading process used for fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides significantly improved the performance of DSSCs and that the improvement in the DSSC performance depends on the thickness of the deposited HfO₂ and Al₂O₃ films. Compared to a reference DSSC the incorporation of a HfO₂ layer resulted in 69% improvement (from 4.2 to 7.1%) in the efficiency of the cell and incorporation of Al₂O₃ (20 cycles) resulted in 19% improvement (from 4.2 to 5.0%) in the efficiency of the cell. These results suggest that ultrathin metal oxide layers affect the density and the distribution of interface states at the TiO₂/organic dye and TiO₂/liquid electrolyte interfaces and hence can be utilized to treat these interfaces in DSSCs.     

Study of electrical and micro-structural properties of high-κ gate dielectric stacks deposited using pulse laser deposition for MOS capacitor applications

The electrical properties of hafnium oxide (HfO₂) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO₂–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (V_fb) and oxide-charge density (Q_ox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La₂O₃ into HfO₂ to fabricate HfO₂/La₂O₃ dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO₂–La₂O₃–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO₂ based MOS capacitors using the PLD deposition technique.     

Thermal stability and mechanical properties of yttria-doped tetragonal zirconia polycrystals with dispersed alumina and silicon carbide particles

Yttria-doped tetragonal zirconia polycrystals in which were dispersed various amounts of Al₂O₃ and SiC particles were sintered at 1500° C for 3 h, and the mechanical properties and the thermal stability of the sintered bodies were evaluated. Dispersion of Al₂O₃ caused no significant effect on sinterability, and increased the hardness and elasticity of the composites. Dispersion of SiC particles decreased the relative density and the grain size of composites. Elasticity and hardness increased by dispersing less than 10 vol% SiC, but decreased above 10 vol% SiC due to the decrease of relative density. Dispersion of both Al₂O₃ and SiC particles slightly increased the fracture toughness of ZrO₂-3 mol% Y₂O₃ ceramics but significantly decreased that of ZrO₂-2 mol% Y₂O₃ ceramics. The rate of the tetragonal-to-monoclinic phase transformation decreased by dispersing both Al₂O₃ and SiC particles. The transformation depth increased rapidly and then slowly with increasing the annealing time. The rate of increase in the transformation depth greatly decreased by dispersing Al₂O₃ particles.     

Effect of Y3+ codoping on luminescence decays of the 4I13/2 level in Er3+-doped Al2O3 powders prepared by a sol-gel method

The luminescence lifetime of the 0.01 mol.%-0.1 mol.% Er³⁺- and 0–20 mol.% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900°C in a non-aqueous sol-gel method has been investigated to explore the enhanced mechanism of photoluminescence properties of the Er³⁺-doped Al₂O₃ by Y³⁺ codoping. For the 0.1 mol.% Er³⁺-Y³⁺-codoped Al₂O₃ powders, the measured lifetime of Er³⁺ gradually increases with increasing Y³⁺ concentration. Consequently, codoping with 20 mol.% Y³⁺ leads to an increase in the measured lifetime from 3.5 to 5.8 ms. By comparing the measured lifetime for different Er³⁺ concentrations in the Al₂O₃ powders, the radiative lifetime of both the Er³⁺-doped and the Er³⁺-Y³⁺-codoped Al₂O₃ powders is estimated to be about 7.5 ms. Infrared absorption spectra indicate that Y³⁺ codoping does not change the-OH content in the Er³⁺-Y³⁺-codoped Al₂O₃ powders. The prolonged luminescence lifetime of the ⁴I_13/2 level of Er³⁺ in Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping is ascribed to the decrease in the energy transfer rate between the Er³⁺ ions and the Er³⁺ and -OH, respectively, due to the suppressed interaction between Er³⁺ ions.     

Microstructure, electrical and dielectric properties, and impulse clamping characteristics of ZnO–V2O5–Mn3O4 semiconducting ceramics modified with Er2O3

This study focuses on the effect of Er₂O₃ on microstructure, electrical and dielectric properties, and impulse clamping characteristics of the ZnO–V₂O₅–Mn₃O₄ varistor ceramics. Analysis of the microstructure indicated that the ZnO–V₂O₅–Mn₃O₄–Er₂O₃ ceramics consisted of major ZnO grain and minor secondary phases such as Zn₃(VO₄)₂, ZnV₂O₄, ErVO₄, and VO₂. As the amount of Er₂O₃ increased, the densities of sintered pellets increased from 5.46 to 5.52 g/cm³, whereas the average grain size decreased from 7.2 to 6.0 μm. The breakdown field increased from 1,016 to 3,185 V/cm with an increase in the amount of Er₂O₃. The highest nonlinear coefficient was obtained at the varistor modified with 0.1 mol%, reaching α = 30. The clamp voltage ratio (K), which indicates an impulse absorption capability, was improved with an increase in the amount of Er₂O₃ and the varistor modified with 0.25 mol% exhibited the best K = 2.41.     

Influence of TiO2 incorporation in HfO2 and Al2O3 based capacitor dielectrics

Atomic layer deposition was applied to fabricate metal oxide films on planar substrates and also in deep trenches with appreciable step coverage. Atomic layer deposition of Ru electrodes was realized on planar substrates. Electrical and structural behaviour of HfO₂-TiO₂ and Al₂O₃-TiO₂ nanolaminates and mixtures as well as Al₂O₃ films were evaluated. The lowest leakage current densities with the lowest equivalent oxide thickness were achieved in mixed Al₂O₃-TiO₂ films annealed at 700 °C, compared to all other films in as-deposited state as well as annealed at 900 °C. The highest permittivities in this study were measured on HfO₂-TiO₂ nanolaminates.