Stability Of Amorphous Phase Research Articles

Phase-change material-based nanoantennas with tunable radiation patterns.

We suggest a novel switchable plasmonic dipole nanoantenna operating at mid-infrared frequencies that exploits phase-change materials. We show that the induced dipole moments of a nanoantenna, where a germanium antimony telluride (Ge3Sb2Te6 or GST for short) nanopatch acts as a spacer between two coupled metallic nanopatches, can be controlled in a disruptive sense. By switching GST between its crystalline and amorphous phases, the nanoantenna can exhibit either an electric or a balanced magneto-electric dipole-like radiation. While the former radiation pattern is omnidirectional, the latter is directive. Based on this property exciting switching devices can be perceived, such as a metasurface whose functionality can be switched between an absorber and a reflector. The switching between stable amorphous and crystalline phases occurs on timescales of nanoseconds and can be achieved by an electrical or optical pulse.

On the role of Sm in solidification of Al-Sm metallic glasses

During the solidification of Al-Sm metallic glasses the evolution of the supercooled liquid atomic structure has been identified with an increasing population of icosahedral-like clusters with increasing Sm concentration. These clusters exhibit slower kinetics compared to the remaining clusters in the liquid leading to enhanced amorphous phase stability and glass forming ability (GFA). Maximum icosahedral-ordering and atomic packing density have been found for the Al90Sm10 and Al85Sm15 alloys, respectively, whereas minimum cohesive energy has been found for the Al93Sm7 which is consistent with the range of compositions (from Al92Sm8 to Al84Sm16) found experimentally with high GFA.

Optical, structural and electrical characterizations of stacked Hf-based and silicon nitride dielectrics

High-k stacked dielectric structures were fabricated by a combination of RF magnetron sputtering and plasma-enhanced chemical vapor deposition. Their structural properties were studied versus deposition and annealing conditions by means of attenuated total reflection and high-resolution transmission electron microscopy techniques. All samples demonstrated smoothed surface (with a roughness below 1nm) and abrupt interfaces between the different stacked layers. No crystallization of Hf-based layers was observed after annealing at 800°C for 30min, demonstrating their amorphous nature and phase stability upon annealing. Uniform capacitance–voltage characteristics were measured along the wafers for all stacks. Besides, after round-voltage sweep they demonstrate significant flat-band voltage hysteresis due to charging of the stack caused by carrier injection from the substrate. These phenomena were found to be more pronounced for the stacks with pure HfO2 layers. The stacked structures were implemented for the formation of Ge nanocrystals by means of ion implantation followed by the thermal treatment mentioned above. It was found that the spatial distribution of Ge crystallites in stacked dielectrics affects significantly their electrical properties including the trapping of charge.

Characterization, thermal stability, and solid-state phase transition behaviors of gestodene polymorphs and amorphous phase

In the current work, a systematic investigation on the thermal behavior of gestodene was carried out to understand temperature induced solid-state transitions between its polymorphs and amorphous phase. The focus was on polymorph identification, thermal stability analysis, and the nature of the phase transitions. These characteristics were compared to the complexity of the phase transitions, studied by differential scanning calorimetry (DSC) and variable temperature X-ray powder diffraction (VT-XRD) techniques. DSC studies indicated that the form II was enantiotropically related to form I, which melted at about 470 K. The temperature of polymorphic transition was 309 K, and form II was the more stable form between room temperature and the transition temperature. A schematic Gibbs free energy-temperature diagram was subsequently constructed to describe the thermal stability of the two forms. Amorphous phase converted exothermically to form I at 368 K on heating and was shown by VT-XRD to be accompanied by diffraction pattern changes. In addition, the crystallization kinetics studied by DSC heating technique followed by analysis using the Kissinger–Akahira–Sunose (KAS) method where values of apparent activation energy (E a) were estimated as a function of extent of conversion (α). The variations in E a with α on kinetic analysis from α = 0.10 to 0.88 for the amorphous to form I conversion suggested more complex processes, possibly liquid–solid and solid–solid transformations prior to formation of the form I.

Amorphous biogenic calcium oxalate

Transition from an amorphous to a crystalline phase and stabilization of amorphous phases is a common strategy in biomineralization. Although no such phenomenon has yet been reported for biogenic calcium oxalate systems, it was recently demonstrated for synthetic calcium oxalate monohydrate (COM). Here we focused on COM raphides—needle shaped biominerals—synthesized by Duckweed. Although these raphides show some birefringence in polarized light, implying their crystallinity, they diffracted poorly when examined by x-ray diffraction in our experiments. By means of transmission electron microscopy coupled with electron diffraction experiments we demonstrated that raphides from Duckweed are completely amorphous in their tip region and transform into a crystalline phase under the electron beam after a few seconds of exposure. To the best of our knowledge, this is the first report on biogenic amorphous calcium oxalate produced by a living organism.

Capacity fading in Li3MnO4: A post-mortem analysis

Li3MnO4, a Mn5+-containing phase, is a promising cathode material for Li-ion batteries due to its very high theoretical capacity of 698Ah/kg. However, the possibility to exploit only part of the theoretical capacity and its rapid capacity fading prevents the use in Li-ion batteries. An ex-situ post mortem analysis combining XRD, SEM, XPS and Raman measurements revealed that lithium extraction or insertion gives rise to amorphization of the structure with conversion to a more stable amorphous MnO2 phase, already after the first cycle. Formation of solid electrolyte interface on the surface of the particles during discharge and its dissolution during charge was also demonstrated. In conclusion, a model for the degradation mechanism of Li3MnO4 in Li-ion batteries was proposed.

Uniform silicon carbide doped Sb2Te nanomaterial for high temperature and high speed PCM applications

Sb–Te alloy is widely considered as one of the important materials for phase change memory (PCM) with fast operation speed. However, the poor amorphous phase stability limits its wide application. In this work, silicon carbide (SiC) doped Sb2Te (Sb2Te-SiC) nanomaterial was proposed to improve the thermal stability of Sb2Te. It was found that the crystallization temperature of Sb2Te was remarkably improved from 149 °C to 251 °C. Accordingly, the temperature for 10-year data retention increases from 56.5 °C to 156.4 °C. X-ray diffraction and transmission electron microscope results indicate that the grain size of Sb2Te-SiC film was largely reduced with SiC doping. Besides, experimental results show the Sb2Te-SiC nanomaterial is very uniform and no phase separation was observed even after 300 °C annealing. Furthermore, the Sb2Te-SiC nanomaterial based PCM cells show fast operation speed of 7 ns and good endurance ability of 2.1 × 104 cycles.

Amorphous Calcium Carbonate Based-Microparticles for Peptide Pulmonary Delivery.

Amorphous calcium carbonate (ACC) is known to interact with proteins, for example, in biogenic ACC, to form stable amorphous phases. The control of amorphous/crystalline and inorganic/organic ratios in inhalable calcium carbonate microparticles may enable particle properties to be adapted to suit the requirements of dry powders for pulmonary delivery by oral inhalation. For example, an amorphous phase can immobilize and stabilize polypeptides in their native structure and amorphous and crystalline phases have different mechanical properties. Therefore, inhalable composite microparticles made of inorganic (i.e., calcium carbonate and calcium formate) and organic (i.e., hyaluronan (HA)) amorphous and crystalline phases were investigated for peptide and protein pulmonary aerosol delivery. The crystalline/amorphous ratio and polymorphic form of the inorganic component was altered by changing the microparticle drying rate and by changing the ammonium carbonate and HA initial concentration. The bioactivity of the model peptide, salmon calcitonin (sCT), coprocessed with alpha-1-antitrypsin (AAT), a model protein with peptidase inhibitor activity, was maintained during processing and the microparticles had excellent aerodynamic properties, making them suitable for pulmonary aerosol delivery. The bioavailability of sCT after aerosol delivery as sCT and AAT-loaded composite microparticles to rats was 4-times higher than that of sCT solution.

Biomimetic mineralization of synthetic collagen-like peptide: a bottom-up approach to design advanced nanocomposite scaffolds for tissue engineering

Event Abstract Back to Event Biomimetic mineralization of synthetic collagen-like peptide: a bottom-up approach to design advanced nanocomposite scaffolds for tissue engineering Gloria Belen Ramirez Rodriguez1, José Manuel Delgado-López2, Michele Iafisco1, Gopal Shankar3, Monica Montesi1, Silvia Panseri1, Monica Sandri1, Simone Sprio1, Bas Kluijtmans4 and Anna Tampieri1 1 Institute of Science and Technology for Ceramic, Bioceramics and Bio-hybrid Composites, Italy 2 Instituto Andaluz de Ciencias de la Tierra, IACT-UGR-CSIC, Spain 3 Rizzoli Orthopaedic Institute, Italy 4 FUJIFILM Manufacturing Europe B.V., TRL Life Science, Netherlands Bone extracellular matrix (ECM) consists in self-assembled nanostructure of proteins (mainly type I collagen) and poor crystalline hydroxyapatite nanocrystals (HA) that surrounds and affects mesenchymal stem cell adhesion, proliferation and differentiation through physico-chemical processes[1]. In attempts to orchestrate in vivo bone environment, we propose biomineralization of a synthetic collagen peptide (SCP, manufactured as CellnestTM by FUJIFILM Europe B.V.). Furthermore, inspired by non-stoichiometric composition of bone apatite, magnesium (Mg) is introduced during mineralization process. Mg controls HA crystallization process as well as can stimulate the osteoblast proliferation[2] and inhibit bacterial adhesion[3]. Variation on morphological and chemical features of HA related to the effect of SCP and Mg during mineralization affect surface nanotopography and consequently micro- and macroscopic interfacial scaffold properties with great relevance on cell interaction. Mineralization of synthetic collagen like-peptide (SCP) was carried out by neutralization process[4] in the absence (SCP-HA) and in the presence of magnesium (SCP-MgHA). The effect of SCP and Mg in HA crystallization was evaluated through the morphological characterization by X-Ray powder diffraction (patterns analyzed by Debye Function Analysis[5]) and transmission electron microscopy (TEM). Chemical analysis was performed by Raman spectroscopy, inductively coupled plasma optical emission spectrometry (ICP-OES) and thermogravimetric analysis. Looking ahead, mineralized solution was directly freeze-dried for the development of porous 3D scaffolds. After that, scaffolds were chemical crosslinked to ensure their stability for long-term biomedical applications. Scaffold surface topography was assessed by High-Resolution Atomic Force Microscopy (HR-AFM). The biological response of MC3T3-E1 cell line to scaffolds was assessed, too. Poor crystalline carbonated HA with similar features to that of bone apatites was synthesized. The amorphous calcium phosphate phase (ACP) was present in all conditions being the main phase in SCP-MgHA mineralization experiments which indicated the synergistic effect of SCP and Mg in stabilization of amorphous phase. Moreover, HR-AFM images of scaffold surface showed that mineralization under this condition (SCP-MgHA) lead to homogeneous mineral distribution while non-covered zones together with isolated HA nanocrystals and/or HA aggregates appeared when mineralization is carried out in the absence of Mg (SCP-HA). MC3T3-E1 cells spread inside the material and exhibited their characteristic morphology which could indicate the osteoconductive effects of designed scaffolds. Figure 1. 3D HR-AFM images of non-mineralized and mineralized scaffold surface as well as surface roughness in terms of root mean square (RMS) roughness (Rq) for scan area 2.5µm x 2.5 µm. Figure 2. SEM micrographs of MC3T3-E1 cells attached to non-mineralized and mineralized scaffolds after 7 days of culture. Herein, we propose biomineralization as a versatile route for the development of biomaterials for bone tissue engineering from nano- to macro-scopic scale. The introduction of foreign ions during mineralization allows us to modify physico-chemical properties that cue cell behavior. In our studies, synergistic effect of SCP and Mg on mineralization provided a homogeneous amorphous mineral distribution triggering to a more resorbable biomaterial. In vitro studies showed that cells attached, proliferated and colonized the scaffolds after 7 days. The research leading to these results has received funding from the European Union Seventh Framework Programme FP7-PEOPLE-2013-ITN under grant agreement n 607051

Thermodynamic Properties of Multicomponent Amorphous Alloys in Fe–Si–B–Ni and Fe–Si–B–Ni–Co–Cr–Mo Systems

The chemical potential of iron in a amorphous phase of multicomponent multiphase alloys Fe – 7.3 % Si – 14.2 % B – 8.26 % Ni (alloy 1) and Fe – 0.32 % Si – 4.8 % B – 6.68 % Ni – 2.42 % Co – 8.88 % Cr – 6.42 % Mo (alloy 2), which contain crystalline and amorphous phases, was determined on the basis of experimental results and a theoretical model. The alloys were produced by melt quenching at a cooling rate of the order of 10 5 K/s and subsequent mechanical milling in an attritor, which resulted in an increase in the fraction of the amorphous phase and improvement of its thermal stability. The chemical potential of iron in a non-equilibrium alloy containing an amorphous phase and crystalline phases (iron-base α-solid solution, FeB, Fe2B, FeSi and other compounds) was determined by an electrochemical method. In order to define the chemical potential of iron in the amorphous phase from the results of electrochemical measurements, a thermodynamic model was developed using the CALPHAD approach for crystalline phases and the SGTE database for pure elements. To evaluate the enthalpy and entropy contribution to the chemical potential of Fe in amorphous phases, the theory of mismatch entropy was employed. It is found that milling in the attritor improves the stability of multicomponent amorphous phases in the above systems, which can be attributed to changes in the cluster-atomic structure of an amorphous phase due to intensive plastic deformation.

On the thermodynamically stable amorphous phase of polymer-derived silicon oxycarbide.

A model for the thermodynamic stability of amorphous silicon oxycarbide (SiCO) is presented. It builds upon the reasonably accepted model of SiCO which is conceived as a nanodomain network of graphene. The domains are expected to be filled with SiO2 molecules, while the interface with graphene is visualized to contain mixed bonds described as Si bonded to C as well as to O atoms. Normally these SiCO compositions would be expected to crystallize. Instead, calorimetric measurements have shown that the amorphous phase is thermodynamically stable. In this article we employ first-principles calculations to estimate how the interfacial energy of the graphene networks is favorably influenced by having mixed bonds attached to them. We analyze the ways in which this reduction in interfacial energy can stabilize the amorphous phase. The approach highlights how density functional theory computations can be combined with the classical analysis of phase transformations to explain the behavior of a complex material. In addition we discover a two-dimensional lattice structure, with the composition Si2C4O3 that is constructed from a single layer of graphene congruent with silicon and oxygen bonds on either side.

Role of Magnesium-Stabilized Amorphous Calcium Carbonate in Mitigating the Extent of Carbonation in Alkali-Activated Slag

Oil well cements have received a significant amount of attention in recent years due to their use in high-risk conditions combined with their exposure to extremely aggressive environments. Adequate resistance to temperature, pressure, and carbonation is necessary to ensure the integrity of the well, with conventional cements prone to chemical degradation when exposed to CO2 molecules. Here, the local atomic structural changes occurring during the accelerated carbonation (100% CO2) of a sustainable cement, alkali-activated slag (AAS) have been investigated using in situ X-ray diffraction and pair distribution function analysis. The results reveal that the extent of carbonation-induced chemical degradation, which is governed by the removal of calcium from the calcium-alumino-silicate-hydrate (C-A-S-H) gel, can be reduced by tailoring the precursor chemistry; specifically the magnesium content. High-magnesium AAS pastes are seen to form stable magnesium-containing amorphous calcium carbonate phases, which pr...

Ab initio calculations of materials selection of oxides for resistive random access memories

The energies of various atomic processes in resistive random access memories (RRAM) are calculated for four typical oxides, HfO2, TiO2, Ta2O5 and Al2O3, to define a materials selection process. Oxygen vacancies have the lowest defect formation energy in the O-poor limit, and to dominate the processes. A band diagram defines the operating ranges of Fermi energy and O chemical potential. It is shown how scavenger metals can be used to vary the O chemical potential and thus vary the O vacancy formation energy. The high stability of amorphous phase of Ta2O5 is relevant to the high endurance of its RRAM.

STUDY ON FORMATION AND CORROSION RESISTANCE OF AMORPHOUS ALLOY IN U-Co SYSTEM

The formation of amorphous phase has been investigated in U-Co system over a wide range of compositions, namely, UxCo100-x (x=50~87.5) by mean of melt-spinning. Phase identification for the arc-melted ingots and rapidly quenched alloys, and the thermal stability of the amorphous phases thus formed have been examined by XRD and DSC, respectively. The component phases in the ingot alloys were structurally the same as those presented in UCo phase diagram, but were associated with a certain compositional metastability. Rapid quenching experiment revealed that the ease of formation of amorphous phase occurred within the composition range of 58.5≤x≤78, and amorphous phase was most readily formed in the vicinity of U66.7Co33.3 composition. The dynamical crystallization temperatures of the amorphous phases were determined to be 534~550 K at a DSC heating rate of 20 K/min, and the highest reduced crystallization temperature (relative to the liquidus temperature) as *国防基础科研计划项目B1520133007和中国工程物理研究院科技发展基金项目2013A0301015资助 收到初稿日期: 2014-10-27,收到修改稿日期: 2015-02-02 作者简介:黄火根,男, 1980年生,副研究员,博士 DOI: 10.11900/0412.1961.2014.00580 第623-630页 pp.623-630

Thermal collapse and hierarchy of polymorphs in a faujasite-type zeolite and its analogous melt-quenched glass.

We examine the route of structural collapse and re-crystallization of faujasite-type (Na,K)-LSX zeolite. As the first step, a rather stable amorphous high density phase HDAcollapse is generated through an order-disorder transition from the original zeolite via a low density phase LDAcollapse, at around 790 °C. We find that the overall amorphization is driven by an increase in the bond angle distribution within T-O-T and a change in ring statistics to 6-membered TO4 (T = Si(4+), Al(3+)) rings at the expense of 4-membered rings. The HDAamorph transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDAMQ, crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDAcollapse which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry.

Aluminum-centered tetrahedron-octahedron transition in advancing Al-Sb-Te phase change properties.

Group IIIA elements, Al, Ga, or In, etc., doped Sb-Te materials have proven good phase change properties, especially the superior data retention ability over popular Ge2Sb2Te5, while their phase transition mechanisms are rarely investigated. In this paper, aiming at the phase transition of Al-Sb-Te materials, we reveal a dominant rule of local structure changes around the Al atoms based on ab initio simulations and nuclear magnetic resonance evidences. By comparing the local chemical environments around Al atoms in respective amorphous and crystalline Al-Sb-Te phases, we believe that Al-centered motifs undergo reversible tetrahedron-octahedron reconfigurations in phase transition process. Such Al-centered local structure rearrangements significantly enhance thermal stability of amorphous phase compared to that of undoped Sb-Te materials, and facilitate a low-energy amorphization due to the weak links among Al-centered and Sb-centered octahedrons. Our studies may provide a useful reference to further understand the underlying physics and optimize performances of all IIIA metal doped Sb-Te phase change materials, prompting the development of NOR/NAND Flash-like phase change memory technology.

High thermal stability Sb3Te-TiN2 material for phase change memory application

For phase change memory (PCM) applications, it has been widely accepted that δ phase Sb-Te has fast operation speed and good phase stability. However, the fast growth crystallization mechanism will cause poor amorphous phase stability and overlarge grain size. We introduce TiN2 into δ phase Sb-Te (Sb3Te) to enhance the amorphous thermal stability and refine the grain size. With TiN2 incorporating, the temperature for 10-year data retention increases from 79 °C to 124 °C. And the grain size decreases to dozens of nanometers scale. Based on X-ray photoelectron spectroscopy and transmission electron microscopy results, we knew that nitrogen atoms bond with titanium, forming disorder region at the grain boundary of Sb3Te-TiN2 (STTN). Thus, STTN has a quite different crystallization mechanism from Sb3Te. Furthermore, PCM device based on STTN can realize reversible phase change under 20 ns electrical pulse.

Fabrication, solid state characterization and bioavailability assessment of stable binary amorphous phases of Ritonavir with Quercetin

In the current study, Quercetin (QRT) was characterized for thermodynamic and kinetic parameters and found as an excellent glass former. QRT was paired with Ritonavir (RTV) (BCS class-IV antiretroviral) to form stable amorphous form and pharmacologically relevant combination. Binary amorphous forms of RTV and QRT in molar ratios 1:1, 1:2 and 2:1 were prepared by solvent evaporation technique and characterized by XRPD, DSC and FTIR. The prepared binary phases were found to become amorphous after solvent evaporation which was confirmed by disappearance of crystalline peaks from X-ray diffractograms and detecting single Tg in DSC studies. The physical stability studies at 40°C for 90days found RTV:QRT 1:2 and RTV:QRT 2:1 phases stable, while trace crystallinity was detected for 1:1M ratio. The temperature stability of RTV:QRT 1:2 and RTV:QRT 2:1 amorphous forms can be attributed to phase solubility of both components where the drug in excess acts as a crystallization inhibitor. Except for RTV:QRT 1:2 ratio, there was no evidence of intermolecular interactions between two components. Almost 5 fold increase in the saturation solubility was achieved for RTV, compared to crystalline counterpart. While for QRT, the solubility advantage was not achieved. In vivo oral bioavailability study was conducted for 1:2 binary amorphous form by using pure RTV as a control. Cmax was improved by 1.26 fold and Tmax was decreased by 2h after comparing with control indicating improved absorption. However no significant enhancement of oral bioavailability (1.12 fold after comparing with control) was found for RTV.

Materials selection for oxide-based resistive random access memories

The energies of atomic processes in resistive random access memories (RRAMs) are calculated for four typical oxides, HfO2, TiO2, Ta2O5, and Al2O3, to define a materials selection process. O vacancies have the lowest defect formation energy in the O-poor limit and dominate the processes. A band diagram defines the operating Fermi energy and O chemical potential range. It is shown how the scavenger metal can be used to vary the O vacancy formation energy, via controlling the O chemical potential, and the mean Fermi energy. The high endurance of Ta2O5 RRAM is related to its more stable amorphous phase and the adaptive lattice rearrangements of its O vacancy.

Stabilization of amorphous paracetamol based systems using traditional and novel strategies

There is a special interest in having pharmaceutical active ingredients in the amorphous state due to their increased solubility and therefore, higher bioavailability. Nevertheless, not all of them present stable amorphous phases. In particular, paracetamol is an active ingredient widely known for its instability when prepared in the amorphous state. In the present work thermally stable amorphous binary paracetamol based systems were obtained showing stability on a wide range of temperatures: below its glass transition temperature (Tg) as amorphous solids in the glassy state and above their glass transition temperature, where these materials exist as stable supercooled liquids. To achieve stabilization of the binary paracetamol based system several strategies were applied and optimized, being the selection of the container material a key and novel approach to control the mechanical stress during cooling, eliminating cracks which act as nucleation centers leading to crystallization.