Formation Of Metastable Solid Solutions Research Articles

Oxalatocuprate(ii) hexaammincobalt(iii) as a precursor of metastable solid solutions in the Co–Cu system

The synthesis and characterization of the double complex salts [Co(NH3)6]2[Cu(C2O4)2]3·4H2O and [Co(NH3)6]2[Cu(C2O4)2]3·6H2O was carried out. Subsequent annealing led to the formation of metastable solid solutions.

A facile method to produce rodlike β‐Si3N4 seed crystallites for bimodal structure controlling

Abstractβ‐Si3N4 rodlike seed crystallites were successfully produced by single‐step heat treatment of commercial α‐Si3N4 powder at 1900°C for 20 h under an N2 gas pressure of 980 kPa. The average diameter, length, and aspect ratio of the seed crystallites were 0.73 μm, 1.37 μm, and 1.86, respectively. The α‐ ⇀ β‐Si3N4 phase transformation proceeded mainly at 1900°C, and this temperature was lower than the theoretical α‐Si3N4 dissociation temperature (1933°C) under N2 gas pressure of 980 kPa. The formation of metastable solid solution due to the dissolution of O impurity into the α‐Si3N4 crystal lattice was suggested as the driving force for the present oxide additive‐free α‐ ⇀ β‐Si3N4 phase transformation. β‐Si3N4 ceramics were fabricated by liquid phase sintering promoted by an additive system of 1 wt% MgO with 3 wt% Gd2O3. Starting α‐Si3N4 powder with 10 vol% rodlike β‐Si3N4 seed crystallites prepared in this study and an extended sintering time for up to 20 h at 1950°C resulted in the formation of bimodal microstructure composed of fine matrix grains and large elongated grains originated from the seed crystallites. The β‐Si3N4 ceramics exhibited improved fracture toughness and thermal conductivity of 5.9 ± 0.8 MPa m−1/2 and 109.3 ± 0.4 W m−1 K−1, respectively, retaining a high fracture strength of about 1 GPa.

Metals Coprecipitation with Barite: Nano-XRF Observation of Enhanced Strontium Incorporation.

Coprecipitation can be an effective treatment method for the removal of environmentally relevant metals from industrial wastewaters such as produced waters from the oil and gas industry. The precipitation of barite, BaSO4, through the addition of sulfate removes barium while coprecipitating strontium and other alkaline earth metals even when these are present at concentrations below their solubility limit. Among other analytical methods, X-ray fluorescence (XRF) nanospectroscopy at the Hard X-ray Nanoprobe (HXN) beamline at the National Synchrotron Light Source II (NSLS-II) was used to quantify Sr incorporation into barite. Thermodynamic modeling of (Ba,Sr)SO4 solid solutions was done using solid solution—aqueous solution (SS-AS) theory. The quantitative, high-resolution nano-XRF data show clearly that the Sr content in (Ba,Sr)SO4 solid solutions varies widely among particles and even within a single particle. We observed substantial Sr incorporation that is far larger than thermodynamic models predict, likely indicating the formation of metastable solid solutions. We also observed that increasing barite supersaturation of the aqueous phase led to increased Sr incorporation, as predicted by available kinetic models. These results suggest that coprecipitation offers significant potential for designing treatment systems for aqueous metals' removal in desired metastable compositions. Solution conditions may be optimized to enhance the incorporation of Sr by increasing sulfate addition such that the barite saturation index remains above ∼3 or by increasing the aqueous Sr to Ba ratio.

Microstructural evolution and thermal stability of Fe–Zr metastable alloys developed by mechanical alloying followed by annealing

The effect of Zr (up to 1 at.%) addition on the formation of Fe–Zr metastable alloys and their thermal stability were investigated for their possible nuclear applications. Fe–xZr (x = 0.25, 0.5, 1%) alloys were synthesised by mechanical alloying under a high-purity argon atmosphere using stainless steel grinding media in a SPEX 8000M high energy mill. The milling was conducted for 20 h with a ball-to-powder weight ratio of 10:1. The formation of metastable solid solutions after milling was confirmed from the change in the Gibbs free energy analysis as per Miedema’s model. The microstructural characterisation was carried out by analysis of X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of Zr on the thermal stability of Fe–Zr alloys was investigated by extensive annealing experiments followed by microstructural analysis and microhardness measurements. The stabilisation was found to occur at 800 °C and thereafter, no significant change in the crystallite size was observed for the samples annealed between 800 and 1200 °C. The supersaturated solid solution, especially 1% Zr alloy, found to be highly stable up to 800 °C and the microhardness value of the same measured to be as high as 8.8 GPa corresponding to a crystallite size of 57 nm. The stabilisation effect has been discussed in the light of both the thermodynamic and kinetic mechanisms and the grain size stabilisation is attributed to the grain boundary segregation of Zr atoms and/or Zener pinning by nanoscale precipitation of the Fe2Zr phase.

Formation Mechanisms and Thermodynamic Stability of Domain Structure in Partially (de)Lithiated Olivine Nanoparticles

The mechanism of Li intercalation in olivine LiFePO4 is a subject of intensive study in recent years. The formation of metastable solid solution is now recognized as an important factor in enabling the excellent high-rate performance of this material. On the other hand, phase separation occurs at low to moderate charge/discharge rates or during rest, leading to the domain structures of coexisting LiFePO4 and FePO4 phases. As defects such as cracks and dislocations are frequently nucleated at domain boundaries, understanding the domain formation phenomenon has significant implications for predicting the degradation of olivine cathode. Despite numerous studies, the formation mechanism, morphology and stability of domain structure in olivine remain to be further elucidated. Previously, a notable experimental observation by Chen et al. [1] reveal intriguing ordered LiFePO4/FePO4 domains separated by parallel (100) phase boundaries in chemically delithiated LiFePO4 particles. However, the absence of (010) phase boundaries in this structure is puzzling since the strongly anisotropic Li diffusivity should prefer a facile phase separation in the [010] direction. While 2D depth-averaged models have been employed to explain the observed domain structure [2], more detailed three-dimensional simulations are required to shed light on this issue. In this work, we carried out 3D phase-field simulations and domain energy calculations to examine the phase separation and domain formation mechanism in free-standing, partially (de)lithiated olivine particles. The employed phase-field model quantitatively captures the effects of Li diffusion anisotropy, interface charge transfer kinetics, coherency stress and stress relaxation at particle surface. Our calculations expose the intricate interplay between thermodynamic driving force and kinetic constraints in the domain formation process, and lead to the following findings: 1) Li exchange between [010] diffusion channels crucially influences domain morphology. When such exchange is negligible, a novel, metastable checkboard pattern containing both (100) and (010) phase boundaries emerges from spontaneous phase separation (or spinodal decomposition) along [010]. In comparison, the stripe pattern reported by Chen et al. is thermodynamically more favorable by eliminating the (010) boundaries, but its formation is kinetically viable only when Li transport between [010] channels is allowed by two possible mechanisms, i.e. i) [100] lattice hopping enabled by the presence of defects and ii) inter-channel exchange through electrolyte. Under the circumstance where inter-channel Li transport has a much larger characteristic time than Li diffusion in the [010] direction, we predict that the checkboard structure will exist as an intermediate structure that can be observed experimentally. 2) Periodic domain structure in free-standing olivine particles is a kinetically stabilized feature. When the volume expansion of olivine particles is not severely constrained by their surrounding, theoretical calculations show that both elastic and interface energy stored in a particle decreases monotonically with domain length, dictating that the thermodynamic equilibrium domain structure should have only one phase boundary in the particle. However, the domain structure can be effectively “frozen” at a finite length scale due to the increasingly sluggish domain coarsening kinetics. Simulations show that the kinetically stabilized domain size is proportional to [010] particle thickness, which is consistent with experiment. The metastability of the periodic domain pattern explains why it is not universally observed in olivine particles prepared under similar conditions [3]. This study shows the important role of kinetic constraints in domain structure evolution in LiFePO4, which provides new insights on potential avenues to improve control of domain morphology via engineering the kinetic properties of olivine materials.

Operando studies of nanoscale olivine cathodes for Li-ion batteries

Compounds of interest for ion storage in advanced batteries frequently exhibit phase transformations, driven by large and variable electrochemical driving forces inherent to practical use. Understanding how materials variables (e.g. composition, nanoscale-crystallite size and dynamic electrochemical conditions) affect the phase transition is of vital importance for practical applications as the reversibility and stability of these structural transformations determine the energy, power, and lifetime of the system. Due to its outstanding power, safety and cycle-life olivine LiFePO4 (LFP) has during the past decade become a widely used, and one of the most well-studied, lithium ion battery cathode materials. It is well-established that for LiFePO4 the storage/release of lithium is accompanied by a first-order phase transition between lithiated and delithiated states. However, it would be a mistake to conclude that the behavior of pure LFP is representative of all olivines, in particular the vast range of doped and mixed-metal olivines that are also of interest for their advantageous electrochemical properties.1,2 Utilizing operando synchrotron radiation powder X-ray diffraction (SR-PXD), we demonstrate here, by systematic screening of the electrochemical driven phase transitions in a series of LiMnyFe1-yPO4 (y =0.1-0.8) powders, a completely different phase transformation mode dominated by formation of metastable solid solutions for nanoscale LMFP compared to the binary lithiation states within the extremely well-studied case of LFP. Through Rietveld refinement the misfit strains during phase transformations are examined, revealing small elastic misfits between phases within the extended solid solution regime. On the basis of the time- and state-of-charge dependence of the olivine structure parameters, we propose a coherent transformation mechanism, and finally, we bring evidence that the observed metastability is enabled by particle size reduction to the nanoscale.

Evidence for Continuous Transformation in Mixed Manganese Iron Olivines

In past two decades, tremendous research efforts have been devoted to understanding the phase transformation behavior of olivine type cathode materials, especially LiFePO4 (LFP). It is well known now that insertion/extraction of lithium in LFP is accompanied by a first-order phase transition between lithiated and delithiated states. Various reports have shown that there is 20~30mV voltage gap between charge and discharge within two-phase range. This voltage hysteresis is attributed to the energy barrier to form intermediate compositions on the single particle level and sequential particle-by-particle transition behavior on the multi-particle level. [1-8]In comparison, LiMnyFe1-yPO4 (LMFP), which is isostructural to LFP, shows strikingly different phase transition behavior. Recent operando Synchrotron Radiation Powder X-Ray Diffraction (SR-PXD) study from our group revealed the formation of metastable solid solutions covering an extended composition range in LiMnyFe1-yPO4 (LMFP, y=0.1, 0.2, 0.4), indicating continuous transition behavior on single particle level and simultaneous transition behavior on multi-particle level. Under this scenario, the voltage hysteresis should be vanishingly small, if not zero. [9, 10]In order to determine voltage hysteresis (or zero-current gap), the open-circuit voltage (OCV) of LMFP within the Fe(II)/Fe(III) phase transition region was measured after charging and after discharging to the same composition. The zero-current gap is the difference in OCV under these two conditions. We found that there is no zero-current gap or thermodynamic hysteresis in LMFP (y=0.1, 0.2, 0.4), as shown in Figure 1. This result indicates that the energy barrier for LMFP to accommodate intermediate composition on single particle level is negligible, resulting in continuous phase transition behavior despite the fact that the composition is well within the two-phase field. Also this result supports the hypothesis that phase transition in LMFP (y=0.1, 0.2, 0.4) takes place in many particles simultaneously.This result may be correlated with the observation that LMFP (y<0.6) has better rate capability than LFP at high rates. Under extremely high rates, surface reaction/transport rather than bulk transport/transition may become rate-limiting. For similar materials, the exchange current density should be similar, hence reaction rate may be correlated with the effective surface area. With the phase transition taking place simultaneously in many particles, LMFP (y<0.6) should have higher active surface area and thus superior rate capability under high rates.

Coherent Phase Transformation in Next-Generation Nanoscale Olivine Cathodes

Due to its outstanding power, safety and cycle-life olivine LiFePO4 (LFP) has during the past decade become a widely used, and one of the most well-studied, lithium ion battery cathode materials. It is well-established that for LiFePO4 the storage/release of lithium is accompanied by a first-order phase transition between lithiated and delithiated states. First-order phase transition behavior persists well into the nanosize regime, although increasing mutual miscibility is observed with decreasing particle size.1-4 Consequently, there have been numerous attempt to describe the detailed mechanism of the phase transformation in nano-LFP. Recently, direct observations by oxidation-state-sensitive X-ray microscopy combined with transmission electron microscopy, have been used to show that at intermediate states of charge, nanoparticulate LFP electrodes are primarily a binary mixture of lithiated and delithiated with relative absence of two-phase particles.5 This preference has important implications for the kinetics of storage in the large arrays of nanoscale particles that comprise practical battery electrodes.However, it would be a mistake to conclude that the behavior of pure LFP is representative of all olivines, in particular the vast range of doped and mixed-metal olivines that are also of interest for their advantageous electrochemical properties.4,6 This is illustrated herein through investigation of the phase transformation in nanoscale olivine LiMn y Fe1-y PO4 (LMFP) during dynamic battery operation.LMFP may be regarded as the second generation olivine cathode, as it has both higher energy density than LFP due to higher average voltage, and lesser known, among the highest rate capabilities ever observed for olivine cathodes. It has been suggested7 that this is due to the existence of an intermediate solid solution (here denoted L x MFP) that reduces the misfit strain by breaking the single phase transition (observed for LFP) into two stages, first a transition of MFP to an intermediate phase L x MFP, then between L x MFP and LMFP. However, no clear conclusion has been drawn as to whether the transformations are two-phase first-order reactions or involve formation of solid solutions, which may be metastable. Significant discrepancies are found in the literature between the (x,y)-compositional phase diagrams for LMFP determined computationally versus experimentally (by chemical delithiation of large particle powders).8,9 We demonstrate here, by systematic screening of the electrochemical driven phase transitions in a series of LiMn y Fe1-y PO4 (y = 0.1, 0.2, 0.4, 0.6 and 0.8) powders, that this material exhibits a completely different phase transformation mode dominated by formation of metastable solid solutions for nanoscale LMFP compared to the binary lithiation states within the extremely well-studied case of LFP. The screening is conducted by operando synchrotron radiation powder X-ray diffraction (SR-PXD) during charge and discharge at different C-rates on powders with particle size of ~50, 100 and 150 nm. Through Rietveld refinement (>1000 PXD patterns have been refined for this study) the misfit strains during phase transformations are examined, revealing small elastic misfits between phases within the extended solid solution regime compared to either pure LiFePO4 or LiMnPO4. Hence, on the basis of the time- and state-of-charge dependence of the olivine structure parameters, we propose a coherent transformation mechanism. Finally, we bring evidence that the observed metastability is enabled by particle size reduction to the nanoscale. This work was supported by DOE project number DE-SC0002626. Work at APS was supported by DOE Contract No.DE-AC02-06CH11357. D.B.R. acknowledges the Carlsberg Foundation for funding.(1)Meethong et al. Electrochem. Solid-State Lett. 2007,10,A134. (2)Meethong et al. Adv. Funct. Mater. 2007,17,1115. (3)Meethong et al. Chem. Mater. 2008, 20,6189. (4)Meethong et al. Adv. Funct. Mater. 2009,19,1060 (5)Chueh et al. Nano Lett. 2013,13,866. (6)Chung et al. Nat. Mater. 2002,1,123. (7)Y.-H. Kao, Ph.D. thesis, MIT, 2011. (8)Yamada et al. J. Electrochem. Soc. 2001,148,A1153. (9)Malik et al. Phys. Rev. B 2009,79,214201.

Formation of metastable solid solutions by mechanical alloying of immiscible Ag and Bi

• Ag powders with different Vickers micro-hardness were prepared by ball milling. • They were mechanically alloyed with Bi. • Bi dissolves into Ag exceeding the solubility limits. • Bi dissolution rate and solubility degree depend on the Ag Vickers micro-hardness. This work investigates the effects of the Vickers micro-hardness of Ag powders on the alloying process undergone by Ag 90 Bi 10 powder mixtures submitted to ball milling. The transformation kinetics has been studied by quantitative X-ray diffraction. The experimental findings indicate that Bi gradually dissolves into Ag, finally forming a crystalline solid solution in which thermodynamic solubility limits are largely exceeded. It is shown that the rate of Bi dissolution, and the solubility degree, decrease as the Vickers micro-hardness of Ag powders increases.

Synthesis, structures, and thermolysis of new heterometallic cobalt, nickel, and copper complexes with the [Ru(NO)(NO2)4(OH)]2− anion as a ligand

Heterometallic complexes with pyridine-N-oxide (PyO), Ru(NO)(NO2)4(OH)Ni(PyO)2(H2O)] · CH3COCH3 (I), [{Ru(NO)(NO2)2(μ-NO2)2(μ-OH)Co}2(μ-PyO)] · H2O · CH3COCH (II), and [Ru(NO)(NO2)4(OH)Cu(PyO)2 (III), are isolated in the reactions of Na2[Ru(NO)(NO2)4(OH)] with nitrates of the corresponding metals in the presence of the organic ligand. The compounds synthesized are characterized by IR spectra, thermal analysis, and X-ray diffraction analysis. Depending on the M2+ cation, the ruthenium cation is coordinated through the bidentate (III, Cu2+) or tridentate (I, Ni2+ and II, CO2+) mode involving the bridging OH group and one or two NO2 groups. The thermal decomposition of complex II results in the formation of a Co0.5Ru0.5 solid solution, which is thermodynamically stable under the decomposition conditions. The thermolysis of complexes I and III in a hydrogen atmosphere leads to the formation of metastable solid solutions.

Formation of metastable solid solutions of boron in nickel under mechanochemical synthesis from Ni-B and Ni-Nb-B mixtures

Using high-energy ball milling of Ni87B13 and Ni87 − x Nb x B13 component mixtures (x = 7, 10, 12, 14) for 2 h, nanocrystalline alloys containing fcc solid solutions of Ni〈B〉 and Ni〈Nb,B〉 were obtained. According to the results of X-ray analysis, oversaturated solid solutions of Ni〈B〉 are interstitial solutions; those of Ni〈Nb,B〉 are substitutional solutions or mixed substitutional-interstitial solutions. Upon heating of the alloys, exothermal effects appear on differential scanning calorimetry (DSC) curves; they are attributed to decomposition of metastable solid solutions and to crystallization of the amorphous phase appearing in mechanical alloying. After heating to 720°C, the Ni87B13 alloy contained stable phases of Ni and Ni3B; the Ni75Nb12B13 alloy contained a τ phase (Ni21Nb2B6) and a metastable solid solution of Ni〈Nb〉.

Formation and structure of Ni-Ag layer by electrolytic deposition

Although nickel and silver have the same Bravaislattice and the difference of atom radii is below 15%, the binary system Ni-Ag is generally immiscible in the solid state below 500 ◦C [1]. The reason for this is the positive energy of mixing (+22 kJ/mol [2]). In recent literature the formation of metastable solid solution of Ni-Ag is described [2–4]. The observed solid solution is produced by using PVD-, CVD-techniques, or mechanical alloying. i.e. techniques, which work far from the thermodynamic equilibrium. In the present work, the original aim was to deposit Ni and Ag electrolytically from the same solution as a crystal mixture with very fine grain size. Layers which consist of a ferromagnetic phase (Ni) and a diamagnetic phase (Ag) are very interesting in view of special magnetic applications (i.e. giant magnetoresistance). The layer should consist mainly of a nickel phase and to a lesser extent part of a silver phase. Because of the large difference between the standard potentials of Ni and Ag, the authors used an electrolyte where the concentration of Ag ions is two orders of magnitude lower than the Ni ion concentration. At a strong negative polarization potential (high over-potential), this concentration of silver leads to a transport limited silver deposition and simultaneously to a charge transfer-controlled deposition of nickel. The high negative over-potential should result in a microstructure with very fine grains. The relation of grain size and over-potential is wellknown [5]. Therefore strong negative polarization potentials were chosen in the following study. The electrolyte composition consisted of 0.7 mol/1 NiSO4, 0.002 mol/1 AgNO3 and 0.26 mol/1 C6H5Na3O7. The pH-value of the solution was 5.5 and all depositions were carried out at room temperature (RT). The electrolyte based on the authors’ own experience in the deposition of nickel layers with nanocrystalline microstructure [6] and was slightly modified. All potentials were measured against a Ag/AgC1-reference electrode. The chemical composition of the deposited layer was investigated by an atom absorption spectrometer (AAS 5 Fa. JenaAnalytik). The X-ray diffraction measurements were carried out with a Siemens D 500 diffractometer in Bragg-Brentano geometry. A monochromatic X-ray Co-Kα beam (λ = 0.17889 nm) was used (tsampling per step = 16 s, step size (in 2θ ) = 0.05◦). At the beginning a cyclovoltammogram is shown in Fig. 1. The transport controlled silver deposition at

Thermodynamic Behavior of Various Phases Appearing in the CeZrO4 ‐ CeZrO3.5 System and the Formation of Metastable Solid Solutions

In order to investigate the thermodynamic behavior of t′, t*, and κ phases with the composition, , the equilibrium oxygen partial pressure, pO2, over their mixtures with pyrochlore was measured utilizing an electrochemical cell: . The conclusions described below were derived: the thermodynamic stability of the κ phase is the lowest in the system. The κ phase forms metastable solid solutions with the pyrochlore phase; it was virtually stable around 1123 K. Two kinds of tetragonal phases exist, tet. (high temp.) and tet. (low temp.), which may correspond to t′ and t*, respectively. A change in pO2 corresponding to the phase transitions: κ → t′ and t* ⇄ was observed. The standard Gibbs energies of formation, ΔGo, of κ() and for the reaction: were evaluated from the emf data.

Formation of metastable solid solution in the ZrO2-rich part of the system ZrO2-Al2O3

Formation of metastable solid solution in the ZrO2-rich part of the system ZrO2-Al2O3

Formation of metastable solid solution in the ZrO 2-rich part of the system ZrO 2Al 2O 3

A metastable ZrO 2Al 2O 3 solid solution was successully synthesized by coprecipitation of hydroxides over the range 0 to 25 mol% Al 2O 3. Combined evidence from XRD and Raman spectroscopy shows the presence of two forms t′ ( c/ a ⪢ 1) and t″ ( c/ a = 1) of the ZrO 2 tetragonal structure. 27Al MAS NMR analysis shows the existence of the three sites AlO 4, AlO 5 and AlO 6 in the whole range of the solid solution. Results of this study provide further insight into the nature of the metastable solid solution.

Heteroepitaxy of lattice-matched compound semiconductors on silicon

The heteroepitaxial overgrowth of silicon by nearly lattice-matched compound semiconductors is reviewed in the context of the separation of the chemical problems associated with the initial sealing of the silicon surface by a contiguous epitaxial compound film from the problems associated with the generation of strain during heteroepitaxial growth. Of the mixed compound systems available dilute solid solutions of composition AlxGa1−xNyP1−y and ZnSySe1−y as well as ZnSixGe1−xP are suitable candidates for the exactly lattice-matched epitaxial overgrowth of silicon. Real-time process monitoring by nonintrusive methods is important for gaining an understanding of the epitaxial overgrowth mechanism and for controlling the film properties. A new method, p-polarized reflectance spectroscopy is introduced that provides detailed information about the growth rate per cycle, the bulk optical properties of the film and its topography. Submonolayer resolution is accomplished for thousands of Å of film growth by pulsed chemical beam epitaxy. While the cubic materials considered here generally afford easier control of the electrical and optical properties, the noncubic materials have advantages in the sealing of the silicon surface because of their anisotropic growth and the formation of metastable solid solutions that may permit the graded growth of compound films under exactly lattice-matched conditions. Therefore, no clear-cut preference in the materials selection for nearly lattice-matched overgrowth of silicon by compound semiconductors can be identified at this time.

Ion implantation and annealing of crystalline oxides

The technique of ion implantation is being investigated as a general method for altering the near-surface properties of insulating materials. The primary motivation behind these investigations is to develop ion implantation as a practical means of controlling and improving the near-surface mechanical, optical, or electronic properties of insulators. Changes in these properties depend on the microstructures and compositions developed in the material during the ion implantation process and subsequent thermal treatments. In many cases, structures and compositions can be produced by implantation and thermal annealing that cannot be achieved by conventional techniques. In this work, the response of a wide range of crystalline oxides to ion implantation and subsequent thermal processing will be reviewed. The materials treated here include Al 2 O 3 , LiNbO 3 , CaTiO 3 , SrTiO 3 , ZnO, and MgO, as well as the non-oxide materials Si 3 N 4 and SiC. The response of these insulators to ion implantation varies widely and depends on the specific material, the implantation species and dose, and the implantation temperature. Ion implantation produces displacement and other damage in the near-surface region, and in many cases, the surfaces of originally crystalline insulators are turned amorphous. Thermal annealing can often be used to restore crystallinity to the damaged near-surface region, and additionally, metastable solid solutions can be produced. For a number of oxide materials, the annealing behavior has been studied in detail using both Rutherford backscattering-ion channeling techniques and transmission electron microscopy. These studies show that, in some materials, the annealing behavior is quite simple and takes place by solid-phase epitaxial crystallization where the amorphous-to-crystalline transformation occurs at an interface that moves toward the free surface during the annealing process. In such materials, the regrowth kinetics have been measured, and the associated activation energies for crystallization have been determined. The formation of metastable solid solutions during crystallization of the amorphous phase will also be discussed.

Metastable surface alloys produced by ion implantation, laser and electron beam treatment

Abstract Ion Implantation, Laser and Electron-beam Treatment (LET) of metals have been employed extensively to produce metastable surface alloys. Recent published work on implanted alloys is reviewed first. The dilute implanted alloys (solute concentration <10 at. %) are shown to lead to crystalline metastable solid solutions. At higher solute concentrations, an amorphous phase has been observed for several binary systems and recently for a ternary system. The physical mechanisms at play, are discussed in detail. A review of the surface alloys produced by LET of metals is then presented—with an emphasis on the mechanisms involved. In particular, general criteria governing formation of metastable solid solutions under LET are proposed and shown to have excellent agreement with available data on metals and Si.

Rapid Annealing of Ion Implanted Silicon Structures using a Radiant Light Source

ABSTRACTAsimple radiant light source has been employed to rapidly anneal ion implanted silicon structures at temperatures &gt;1000° C for times of the order of 1–200 sec. Rutherford backscattering and channeling analysis indicated good crystalline lattice recovery and the formation of metastable solid solutions of Sb in Si without observable diffusion broadening of the implanted profile. Diode arrays have been successfully annealed using the technique, with no observable deterioration of the surrounding oxide mask.

Formation of metastable solid solutions in the Pb-Ge system

The formation and decomposition behaviours of metastable solid solutions in liquid-quenched and vapour-quenched Pb-Ge alloys were studied using X-ray diffraction, transmission electron microscopy (TEM), differential thermal analysis (DTA) and resistance measurement techniques. It is shown that the Pb-rich fcc phase can retain upto about 13 at% Ge on liquid-quenching and upto about 5 at% Ge on vapour-quenching. Decomposition of the Pb-rich fcc phase occurs in the temperature range 220 to 300° C and it is a temperature dependent nucleation and growth phenomenon. Upto about 7.5 at% Pb can be retained in Ge-rich compositions in an amorphous Ge matrix on vapour-quenching but there is no detectable solubility of Pb in crystalline Ge retained by liquid-quenching. On heating, the amorphous Ge-Pb films crystallize to a Ge-rich solid solution which decomposes to equilibrium constituents at higher temperatures. Stability of amorphous Ge-Pb films decreases on increasing metal concentration.