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1.
The phase separation and crystallization behavior in the system (80 − X)SiO 2 · X(Al 2O 3 + P 2O 5) · 5B 2O 3 · 15Na 2O (mol%) glasses was investigated. Glasses with X = 20 and 30 phase separated into two phases, one of which is rich in Al 2O 3-P 2O 5-SiO 2 and forms a continuous phase. Glasses containing a larger amount of Al 2O 3-P 2O 5 ( X = 40 and 50) readily crystallize and precipitates tridymite type AlPO 4 crystals. It is estimated that the phase separation occurs forming continuous Al 2O 3-P 2O 5-SiO 2 phase at first, and then tridymite type AlPO 4 crystals precipitate and grow in this phase. Highly transparent glass-ceramics comparable to glass can be successfully obtained by controlling heat treatment precisely. The crystal size and percent crystallinity of these transparent glass-ceramics are 20-30 nm and about 50%, respectively. 相似文献
2.
The solubility of Ag 2O was measured for the Na 2O–B 2O 3 and Na 2O–B 2O 3–Al 2O 3 system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag 2O for the Na 2O–B 2O 3 system above the melting point of Ag for the first time. It was found that the addition of Na 2O decreases the solubility of Ag 2O while the addition of Al 2O 3 had little effect on the solubility. The effect of Na 2O and Al 2O 3 on the solubility of Ag 2O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag 2O in Na 2O–B 2O 3–Al 2O 3 melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver. 相似文献
3.
The changes in the main chemical reactions occurring upon the interaction between tungsten and the evaporation products of
Al 2O 3 melt are considered at a fixed temperature (2400 K). The concentrations of the components coexisting in equilibrium in a
closed system under isobaric-isothermal conditions are determined by stochastic simulation for low (× 10 −1−1 × 10 −3 bar) and high (1 × 10 −4 bar) vacuum. It is shown that the gas-liquid-solid system is in heterogeneous equilibrium for the basic component ratio W:
Al 2O 3 = 1: 1 in the entire pressure range under consideration. A detailed study of the chemistry of this system should facilitate
the choice of the optimal conditions for growing leucosapphire crystals from melt. 相似文献
4.
The immiscibility boundary and the critical point of SiO 2-Nd 2O 3 system glass were determined as a function of Al 2O 3 addition. The critical temperature of the immiscibility boundary was observed to decrease with the addition of Al 2O 3. Using the regular solution model, the observed decrease of the immiscibility boundary was directly related to the decrease of the concentration fluctuation of Nd 2O 3 in SiO 2. It is concluded that the Al 2O 3 addition to Nd 2O 3 containing silica glass is beneficial in decreasing the concentration quenching effect, deterioration of the optical efficiency due to clustering of rare earth element, because Al 2O 3 addition diminishes the concentration fluctuation of Nd 2O 3 in silica glass. 相似文献
5.
The possibility of chemical reactions has been calculated and the composition of the gas and solid phases that are in equilibrium with an aluminum oxide melt is determined. It is shown that, for the Al 2O 3-Mo system in the pressure range 1?1 × 10 ?5 bar, evaporation of Al 2O 3 is incongruent, and the fraction of this component in the gas phase decreases from 51.5 mol % ( P = 1 bar) to 0.01 mol % ( P = 1 × 10 ?5 bar). The presence of molybdenum-containing compounds in the gas phase changes the balance of oxygen and aluminum in favor of the latter (the aluminum partial pressure increases by a factor of 1.5–3), as a result of which there may be an aluminum deficit in the solid phase of Al 2O 3 during crystal growth from a melt. The thermodynamic characteristics ( K p , Δ G, P tot) of dominant chemical reactions have been calculated for the temperature range 2327–2500 K. Understanding of the chemical processes makes it possible to optimize the growth parameters of leucosapphire single crystals. 相似文献
6.
Amorphous Al 2O 3 films were deposited on p-Si by rf magnetron sputtering to investigate their potential as a gate dielectric in organic thin film transistors (OTFTs). The deposition was performed at room temperature, 200 and 300 °C using Al 2O 3 and Al targets. Achieved Al 2O 3 films have higher capacitance values than thermally grown SiO 2 as characterized by capacitance-voltage measurements. It is also found from current-voltage and roughness measurements that the leakage current and the surface roughness can be least when the films are deposited at room temperature. The capacitance of the film obtained from the Al 2O 3 target appears higher than that of the Al 2O 3 film from the Al target while the results of electrical breakdown are opposite. These room temperature processes are promising for applications to the gate dielectrics of organic TFTs. 相似文献
7.
Zr 0.6Al 0.4O 1.8 dielectric films were deposited directly on strained SiGe substrates at room temperature by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N 2 under various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr 0.6Al 0.4O 1.8 film is about 900 °C, 400 °C higher than that of pure ZrO 2. The amorphous Zr 0.6Al 0.4O 1.8 film with a physical thickness of ∼12 nm and an amorphous interfacial layer (IL) with a physical thickness of ∼3 nm have been observed by high-resolution transmission electron microscopy (HRTEM). In addition, it is demonstrated there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800 °C in the Zr 0.6Al 0.4O 1.8 film. The chemical composition of the Zr 0.6Al 0.4O 1.8 film has been studied using secondary ion mass spectroscopy (SIMS). 相似文献
8.
The W–Al 2O 3 system at T = 2400 K and standard pressure (controlled Ar + H 2 atmosphere) has been calculated by stochastic simulation. It is shown that the presence of hydrogen leads to the formation of aluminum hydrides, hydrogen oxides, and aluminum hydroxides; the compounds from the two latter groups (except for water) can interact directly with tungsten. The main chemical reactions occurring in the system are determined, based on which a conclusion about the cyclic character of the processes is drawn. Some recommendations on the composition and pressure of controlled atmosphere for growing sapphire crystals are given. 相似文献
9.
The possibility of formation of molybdenum and tungsten polyoxides in the Mo–W–Al2O3–H2 system at T = 2400 K and P = 1 bar in a controlled Ar + H2 atmosphere has been investigated by the method of thermodynamic analysis. The formation of polyoxides is found to occur both due to the processes involving Al2O3 melt and in the absence of the latter. It is established that metals (Mo and W) and their mono-, di-, and even trioxides (in the latter case, mediated polymerization occurs) can be used as initial components to form polyoxides. It is shown that polyoxides themselves may interact with one of their main sources: Al2O3 melt. 相似文献
10.
The optimum compositions of the melts used for the growth of yttrium-aluminum garnet (YAG) single crystals with different
neodymium contents are determined using the phase diagram of the ternary system Y 2O 3-Al 2O 3-Nd 2O 3 with the binary sections Y 3Al 5O 12-Nd 2O 3 and Y 3Al 5O 12-Nd 3Al 5O 12. A number of melt compositions characterized by one garnet phase, namely, (Y,Nd) 3Al 5O 12, are established. Single crystals of yttrium-aluminum garnets with a high content of the activator (up to 2.6 wt % Nd) are
grown by the Czochralski method.
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Translated from Kristallografiya, Vol. 48, No. 5, 2003, pp. 945–949.
Original Russian Text Copyright ? 2003 by Soboleva, Chirkin.
Dedicated to the 60th Anniversary of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences 相似文献
11.
By rapid quenching in a twin roller apparatus, glass was found to occur widely in the systems of Li 2O with Al 2O 3, Ga 2O 3, Bi 2O 3 and in mixed systems. Examination of the resulting flakes by X-ray powder diffraction, differential thermal analysis, and capacitance data revealed the occurrence of glass, glass transitions, crystallization exotherms and the nature of some of the crystallization paths.The log ionic conductivity of the glasses was found to follow a linear relationship with the Li concentration. Evidence was observed for three new metastable crystalline phases, one in the Li 2OAl 2O 3 system and two in the Li 2OBi 2O 3 system. The latter system also showed evidence for the occurrence of two glasses at almost all compositions. 相似文献
12.
The main chemical reactions between Mo and W polyoxides and Al2O3 melt in a controlled Ar + H2 atmosphere (T = 2400 K, P = 1 bar) during sapphire growth by horizontal directional solidification have been investigated. Under these thermodynamic conditions, the melt and products of its dissociative evaporation may actively react with the tungsten heater and molybdenum thermal screens of the crystallization system. It is shown that the polyoxides formed during evaporation do not directly interact with the melt; this interaction occurs only with participation of reagents exhibiting pronounced reducing properties (Al, H2, H, WO, Al2O, AlH, AlH2, AlH3). It is established that most of processes occur with participation of aluminum hydrides. A particular role of Mo(W) dioxide–W(Mo) polyoxide functional pairs in the interaction with the melt is determined. 相似文献
13.
A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the ternary Al 2O 3–B 2O 3–SiO 2 system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model and the Gibbs energy of the mullite solid solution is modeled using the Compound Energy Formalism. A set of optimized internally consistent thermodynamic functions for all the phases is presented. With the thermodynamic dataset, all available and reliable thermodynamic and phase equilibrium data can be reproduced within experimental error limits from 25 °C to above the liquidus temperatures. In addition, the reasonable predictions obtained for phase relations in the experimentally unexplored composition ranges suggest that the thermodynamic database can be used along with appropriate Gibbs energy minimization routines to calculate thermodynamic properties, phase equilibria, and phase diagrams of interest. 相似文献
14.
The phase equilibria in the Ba 2Na 3[B 3O 6] 2F-BaF 2 section, which belongs to the ternary mutual Ba, Na//BO 2,F system, have been studied by the methods of solid-phase synthesis, visual polythermal analysis, and differential-thermal
analyses. It is shown that this section can be used to grow bulk Ba 2Na 3[B 3O 6] 2F crystals. 相似文献
15.
Al 2O 3 and ZrO 2 mixtures for gate dielectrics have been investigated as replacements for silicon dioxide aiming to reduce the gate leakage current and reliability in future CMOS devices. Al 2O 3 and ZrO 2 films were deposited by atomic layer chemical vapor deposition (ALCVD) on HF dipped silicon wafers. The growth behavior has been characterized structurally and electrically. ALCVD growth of ZrO 2 on a hydrogen terminated silicon surface yields films with deteriorated electrical properties due to the uncontrolled formation of interfacial oxide while decent interfaces are obtained in the case of Al 2O 3. Another concern with respect to reliability aspects is the relatively low crystallization temperature of amorphous high- k materials deposited by ALCVD. In order to maintain the amorphous structure at high temperatures needed for dopant activation in the source drain regions of CMOS devices, binary Al/Zr compounds and laminated stacks of thin Al 2O 3 and ZrO 2 films were deposited. X-ray diffraction and transmission electron microscope analysis show that the crystallization temperature can be increased dramatically by using a mixed oxide approach. Electrical characterization shows orders of leakage current reduction at 1.1-1.7 nm of equivalent oxide thickness. The permittivity of the deposited films is determined by combining quantum mechanically corrected capacitance voltage measurements with structural analysis by transmission electron microscope, X-ray reflectivity, Rutherford backscattering, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectroscopy. The k-values are discussed with respect to formation of interfacial oxide and possible silicate formation. 相似文献
16.
The atomic layer chemical vapor deposition (ALCVD) deposited Al 2O 3 and ZrO 2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al 2O 3) or 0.6 nm (ZrO 2), the band gaps of the Al 2O 3 and ZrO 2 films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al 2O 3/Si and ZrO 2/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al 2O 3 and Zr 3p3 in ZrO 2 are 2.7 and 2.0 nm, respectively. 相似文献
17.
A small-angle X-ray diffraction study of the supercritical region of the B 2O 3PbOAl 2O 3 immiscibility surface is presented. This is the first time that diffraction methods have been applied to the study of critical opalescence in a system of oxides at high temperatures. Debye's theory is shown to be applicable and, from the spectra correlation lengths and the range of molecular interactions l is calculated. The topography of the supercritical region is determined and the relationship between l and the main interatomic distances in the melt discussed. 相似文献
18.
The current structural models have been used to analyse the refractive index data of Na 2O-Al 2O 3-SiO 2 glasses (Al 2O 3/Na 2O?1). The SiO 2 content is the sole factor that controls the refractive index. Values could be obtained for the factors with which each structural unit contributes in the refractive index. The content of Al 2O 3 or Na 2O has no effect on the refractive index. The factors (differential refraction) are constant and do not change with composition. They have the same values for Na 2O-SiO 2 glasses. The differential refraction of a structural unit increases linearly with increasing the number of non-bridging oxygen ions. The difference of the contribution to the refractive index from a silicate unit to the next equals to a half of that for AlO 4 tetrahedron. The effect could be attributed to the change in both the concentration and differential refraction of structural units. The obtained factors for the structural units are useful in calculating the refractive index with a high degree of accuracy. 相似文献
19.
Al 2O 3-Mo and Al 2O 3-W systems in a controlled Ar(95%) + H 2(5%) atmosphere at T = 2400 K and P = 1 bar have been calculated by the Monte Carlo method. It is established that the presence of hydrogen in these systems leads to the occurrence of OH, H 2O 2, HO 2, H 2O, AlOH, AlOOH, AlH, AlH 2, and AlH 3 components in the gas phase; aluminum hydrides are formed only through the interaction of hydrogen with melt evaporation products. The presence of reducing medium leads to a decrease in the free oxygen concentration by one to two orders of magnitude, which is expected to improve the quality of sapphire crystals. 相似文献
20.
Thin Al 2O 3 layers were grown by atomic layer deposition using trimethylaluminum (TMA) and water as precursors on 1.2 nm thermal SiO 2 and HF cleaned Si surfaces. The stoichiometry and the contamination (H, OH and C) of as-deposited and N 2 annealed thick Al 2O 3 layers were characterized by secondary ion mass spectrometry (SIMS), elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). We show a perturbed region (≈5 nm thick) at the Al 2O 3/Si interface by XPS and Auger electron spectrometry (AES). Post-deposition annealings induced important interface oxidation, Si atoms injection and SiO 2/Al 2O 3 mixture whereas the initial interface was abrupt. Silicon oxidation before Al 2O 3 growth highly limits interfacial oxidation and improves interfacial quality. We proposed that OH groups may play a key role to explain silicon oxidation during post-deposition annealings in inert ambience with low oxygen contamination levels. 相似文献
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