Phase Separation of β-SN in Strained, Compositionally Metastable Ge1-xSnx Alloys

1995 ◽  
Vol 398 ◽  
Author(s):  
Joshua W. Kriesel ◽  
Susanne M. Lee
Keyword(s):  
Phase Separation ◽  
Electron Microprobe ◽  
Rf Sputtering ◽  
Melting Behavior ◽  
Solubility Limit ◽  
X Ray Diffraction ◽  
Solid Solubility Limit ◽  
Transformation Mechanisms ◽  
Subsequent Phase ◽  
Kinetics Of

ABSTRACTUsing rf sputtering and post-deposition annealing in a differential scanning calorimeter (DSC), we manufactured bulk (4000 nm) films of crystalline Ge0.83Sn0.17. This Sn concentration is much greater than the solid solubility limit of Sn in Ge (x ≤ 0.01). Continued annealing thermally induces Sn phase separation from the alloy, limiting the ultimate attainable grain size in the metastable crystals. We examine, here, the mechanisms and kinetics of the processes limiting the size of the Ge0.83Sn0.17 polycrystals. From a combination of DSC, electron microprobe, and x-ray diffraction (XRD) measurements, we propose phase transformation mechanisms corresponding to crystallization of amorphous Ge0.83Sn0.17, crystallization of an as-yet unidentified phase of Sn, and phase separation of Sn from the Ge1-xSnx crystals. We were unable to observe the unidentified phase of Sn in XRD, but the phase must be present in the material to account for the quantitative discrepancies (as much as 8 at.%) in Sn percentages determined from each of the DSC, XRD, and electron microprobe measurements. Our models for the various transformation kinetics were corroborated by the subsequent phase-separated Sn melting behavior observed in the DSC: two Sn melting endotherms, one of which was 20–100°C lower than the bulk melting temperature of Sn. This depressed temperature endotherm we speculate represents liquefaction of nanometer-sized (β–Sn clusters.

In situ high temperature X-ray diffraction study of the kinetics of phase separation in the uranium-plutonium mixed oxide (U0.55Pu0.45)O2-x

2014 ◽  
Vol 1645 ◽  
Author(s):  
Romain VAUCHY ◽  
Renaud.C. BELIN ◽  
Anne-Charlotte ROBISSON ◽  
Fiqiri HODAJ
Keyword(s):  
Phase Separation ◽  
Room Temperature ◽  
Mixed Oxides ◽  
Oxygen Stoichiometry ◽  
X Ray Diffraction ◽  
Fundamental Interest ◽  
X Ray ◽  
Uranium Plutonium ◽  
Kinetics Of

ABSTRACTUranium-plutonium mixed oxides incorporating high amounts of plutonium are considered for future nuclear reactors. For plutonium content higher than 20%, a phase separation occurs, depending on the temperature and on the oxygen stoichiometry. This phase separation phenomenon is still not precisely described, especially at high plutonium content. Here, using an original in situ fast X-ray diffraction device dedicated to radioactive materials, we evidenced a phase separation occurring during rapid cooling from 1773 K to room temperature at the rate of 0.05 and 2 K per second for a (U0.55Pu0.45)O2-x compound under a reducing atmosphere. The results show that the cooling rate does not impact the lattice parameters of the obtained phases at room temperature but their fraction. In addition to their obvious fundamental interest, these results are of utmost importance in the prospect of using uranium-plutonium mixed oxides with high plutonium content as nuclear fuels.

Effects of Post-Deposition Processing on the Ultimate Grain Size in Metastable Semiconductor Thin Films to be Used in IR Detectors

1994 ◽  
Vol 343 ◽  
Author(s):  
Susanne M Lee
Keyword(s):  
Thin Films ◽  
Thick Films ◽  
Rf Sputtering ◽  
Solubility Limit ◽  
Nucleation And Growth ◽  
Separation Mechanism ◽  
Post Deposition Annealing ◽  
Ir Detectors ◽  
Solid Solubility Limit ◽  
Post Deposition

ABSTRACTThrough post-deposition annealing in a differential scanning calorimeter (DSC), we have manufactured both thin (200 nm) and bulk (8000 nm) single phase films of crystalline Ge1–xSnx, using rf sputtering. The Sn concentrations produced ranged up to 31 at.%, well beyond the solid solubility limit of this system. There was a marked difference, in the asdeposited structure, between thick and thin films produced under the same deposition conditions. Quantitative models for both systems are given in this paper and were deduced frorn DSC measurements in conjunction with electron microscopy. The metastable crystalline state in the thin films formed by nucleation and growth from an amorphous phase; whereas in the thick films, the desired phase was already present in the as-deposited films and only growth of preexisting grains was observed upon post-deposition annealing. When annealed to high temperature, the Sn phase separates from the alloys and we postulate here that it does so by nucleation and growth of β-Sn. With this hypothesis, the Sn separation in the 8000 nm thick films was accurately modeled by a two-mechanism process, however, in the 200 nm thick films, only one phase separation mechanism was necessary to accurately fit the data. Both models were corroborated by the subsequent melting behavior of the phase separated Sn which, though it varied depending on the sample being measured, always exhibited a melting endotherm starting 25–35°C lower than the bulk melting temperature of Sn. Speculation on the reasons for this are presented.

Pd2Si on Si(111) Growth Kinetics Studied by X-Ray Diffraction

1984 ◽  
Vol 37 ◽  
Author(s):  
Betty Coulman ◽  
Haydn Chen
Keyword(s):  
Growth Kinetics ◽  
Electron Microprobe ◽  
Qualitative Agreement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Rate Law ◽  
Interfacial Layers ◽  
Diffusion Paths ◽  
Si Films ◽  
Kinetics Of

AbstractResults are presented for the kinetics of growth of Pd2Si interfacial layers obtained by an X-ray diffraction technique. Epitaxial Pd2Si films were grown on Si(111) substrates over a temperature range of 160–222°C. The parabolic rate law observed is in qualitative agreement with those reported by investigators using other techniques (RBS, AES, Electron Microprobe). There appear to be two kinetics regimes distinquished by diffusion paths with different activation energies (1.35±0.10 eV vs. 1.05± 0.10 eV). The presence of impurities and the detailed Pd 2Si microstructure will influence how the reacting species are transported through the lattice.

Amorphous/Crystalline Structure And Phase Transformations In Metastable Semiconducting Ge1−xSnx

1993 ◽  
Vol 321 ◽  
Author(s):  
Susanne M. Lee ◽  
Katayun Barmak
Keyword(s):  
Rf Sputtering ◽  
Solubility Limit ◽  
Scanning Calorimetry ◽  
Solid Solubility Limit ◽  
Electronic Band ◽  
Fine Grained ◽  
Dsc Measurements ◽  
Theoretical Predictions ◽  
Structure And Phase Transformations ◽  
Electronic Band Structures

ABSTRACTThe semiconducting crystalline alloys, Ge1−xSnx, are of interest due to theoretical predictions about their electronic band structures which make them useful in infrared photodetectors. However the composition region where these alloys have the desired properties is greater than the equilibrium solid solubility limit of Sn in Ge (x<0.01). We have circumvented the solubility limits and produced thin (2000Å) and thick (4–8Μm) films of Gei.xSnx (x<0.31) by rf sputtering. Differential scanning calorimetry (DSC) Measurements were performed to study grain growth and crystallization processes in these highly metastable semiconductors. X-ray and electron diffraction measurements indicated the materials were amorphous, but the fact that some of the films were fine grained polycrystalline samples only became apparent in their DSC spectra. We present models that describe quantitatively the transformation behavior in both sets of films.

scholarly journals Studies on the β → α Phase Transition Kinetics of Ti–3.5Al–5Mo–4V Alloy under Isothermal Conditions by X-ray Diffraction

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 90
Author(s):  
Panpan Ge ◽  
Song Xiang ◽  
Yuanbiao Tan ◽  
Xuanming Ji
Keyword(s):  
Phase Transition ◽  
Aging Time ◽  
Solution Temperature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Α Phase ◽  
Precipitate Fraction ◽  
Transformation Mechanisms ◽  
Phase Transition Kinetics ◽  
Kinetics Of

The β → α phase transition kinetics of the Ti–3.5Al–5Mo–4V alloy with two different grain sizes was investigated at the isothermal temperature of 500 °C. A method to estimate the function of the precipitate fraction of the α phase with different aging times was developed based on X-ray diffraction analysis. The value of the α precipitate fraction increased sharply at first, then increased slowly with the aging time, and finally reached equilibrium. The value of the α precipitate fraction was higher in the alloy aged for the same time at a higher solution temperature, while the size of the α precipitate was smaller at a higher solution temperature. The β → α phase transition kinetics under isothermal conditions were modeled in the theoretical frame of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. The kinetic parameters of JMAK deduced different transformation mechanisms. The mechanism of the phase transition in the first stage was dominated by mixed transformation mechanisms (homogeneously nucleated and acicular-grown α structure, and grain boundary-nucleated and grown α precipitate), while the second stage was the growth of the fine α precipitate, which was controlled by slow diffusion. As the aging time increased, the hardness of the Ti–3.5Al–5Mo–4V alloy increased sharply. After the hardness of the alloy reached a plateau, it began to decline. The hardness of the alloy was always higher at a higher solution temperature.

scholarly journals Structure and Microstructure of Y-doped Strontium Titanate Ceramics

2008 ◽  
Vol 14 (S3) ◽  
pp. 11-12 ◽  
Author(s):  
Alexander Tkach ◽  
Paula M. Vilarinho ◽  
Ian M. Reaney
Keyword(s):  
Electron Microscopy ◽  
Solubility Limit ◽  
Second Phase ◽  
X Ray Diffraction ◽  
Solid Solubility Limit ◽  
Local Composition ◽  
Transmission Electron ◽  
High Dielectric ◽  
Titanate Ceramics ◽  
Structure And Microstructure

High dielectric constant important for functional electronic applications have been reported in the Sr1-1.5xYxTiO3 ceramic system with a maximum value for x = 0.01 coincident with the maximum grain size. This observation points to a possible correlation between the dielectric response and the microstructure of these ceramics. A solid solubility limit around x = 0.04 was reported recently by Fu et al., although the second phase was observed by X-ray diffraction only for x = 0.07. Therefore, the structure, microstructure and local composition of Sr1-1.5xYxTiO3 ceramics (x = 0 − 0.05) prepared by conventional mixed oxide method is investigated in this work by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy facilities.

Laser-Induced Solid Phase Crystallization in Amorphous Silicon Films

1982 ◽  
Vol 13 ◽  
Author(s):  
G.L. Olson ◽  
S.A. Kokorowski ◽  
J.A. Roth ◽  
L.D. Hess
Keyword(s):  
Solid Phase ◽  
Solubility Limit ◽  
State Theory ◽  
Solid Phase Crystallization ◽  
Solid Solubility Limit ◽  
Time Resolved ◽  
Impurity Atoms ◽  
Intrinsic Kinetics ◽  
Dopant Atoms ◽  
Kinetics Of

ABSTRACTWe review recent work on the kinetics of laser-induced solid phase epitaxial crystallization of silicon as determined from time-resolved reflectivity measurements. Specific topics which are addressed include: the intrinsic kinetics of solid phase epitaxy (SPE) in ion-implanted and UHV-deposited films; SPE rate enhancement by implanted dopant atoms and the effects of electrical compensation on the SPE rate; and the temperature dependence of SPE and competing processes in samples containing impurity atoms at concentrations exceeding the solid solubility limit. The high temperature kinetics results are compared with predictions from transition state theory and are discussed with respect to a proposed depression in the amorphous Si melting temperature.

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