Crystalline Phase Change Research Articles

Modulation of the Pb/Sn ratio in Pb1-xSnxS thin films synthesized by chemical solution deposition

This work presents the development of a formulation for the synthesis of Pb1-xSnxS thin films by chemical bath deposition. The success of this formulation is due to the high miscibility between lead sulfide (PbS) and tin (II) sulfide (SnS). By adding different concentrations of a Pb2+ ions solution to a Sn2+ S2− formulation, we obtain Pb1-xSnxS films with different Pb/Sn ratio. The presence of Pb2+ in those films is confirmed by X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Structural analysis by X-ray diffraction (XDR) shows a crystalline phase change from an SnS orthorhombic structure (00.00 mmol Pb2+) to a solid solution where the orthorhombic and cubic structures coexist (30.00 mmol Pb2+), and finally reaching the formation of a cubic PbS structure. Changes in the morphology of the films are observed together with the incorporation of Pb2+ ions in the films, reducing the size of nano-flakes and becoming a more compact layer, leading to a decrease in the film thickness from 370 nm (00.00 mmol Pb2+) to 96 nm (50.00 mmol Pb2+). The decrease of the energy band gap (Eg) of the samples from 1.92 to 1.38 eV with the increase of the Pb2+ concentration is also observed, obtaining wide absorption spectra from visible to near-infrared.

Piezoelectric-piezocapacitive hybrid sensor based on electrospun Poly(vinylidene fluoride)-Poly(octafluoropentyl acrylate)-sulphonated Poly(phenylene sulfide) blend nanofiber

In this study, sulfonated Poly(phenylidene sulfide) (sPPS) of varying content (0, 3, 5, 7 and 10 wt.-%) is used as a filler to study the β-crystalline phase changes in electrospun Poly(vinylidene fluoride) (PVDF)-Poly(octafluoropentyl acrylate) (POFPA) blend (90/10 ratio, abbreviated as P-PFA) nanofiber. FTIR and XRD studies confirmed the changes in P-PFA crystalline phases as a function of varying sPPS content, and among them, 5 wt.-% sPPS content exhibited a maximum increase in β-crystallinity. SEM micrographs of P-PFA/sPPS confirmed the appropriate formation of nanofibers with average fiber diameters of around 90 ∼ 150 nm. Using electrospun neat P-PFA and P-PFA/sPPS blend nanoweb fibers, piezoelectric sensors were fabricated and measured for output voltage signals. Among the five different samples, P-PFA/sPPS (5 wt.-%) exhibited higher output voltage (Vp-p = 1.2 V) than neat P-PFA (Vp-p = 0.4 V), revealing the nucleating effect of sPPS in P-PFA. The unexpected values obtained in the tensile strength (35.09 ± 0.102 kPa) and capacitance hysteresis (Cmax = 0.158 nF) of P-PFA/sPPS (5 wt.-%) sample opens up the possibility of using this material as a flexible hybrid sensor capable of measuring both piezoelectric and piezocapacitive signals.

Crystalline phase change and improvement in electro-optical parameters of SnSx thin films by different ambients

Crystalline phase change and improvement in electro-optical parameters of SnSx thin films by different ambients

Microstructural changes and mechanical performance of cement composites reinforced with recycled carbon fibers

In recent years, efforts have been made to utilize recycled carbon fibers (RCFs) into the cement composites. However, limited information is available on the interaction of these recycled fibers with the host cement matrix. Therefore, this study aims to provide a better understanding of the influence of milled recycled carbon fibers (RCFs) on cement composites. For this purpose, six different fiber volume fractions ranging from 0.25% to 1.5%, at an increasing rate to 0.25%, were selected to develop fiber-reinforced cement composites, and a comprehensive research study was conducted to investigate the effect of RCFs on strength improvement, microstructure, crystalline phase change, and hydration products of cement composites over time. The X-ray diffraction analysis, FTIR, and thermogravimetric analysis revealed that RCFs promote the growth of hydration products by providing inert nucleation sites without any additional chemical reaction. The degree of hydration and chemically bound water was increased by 6.64% and 1.59%, respectively, when 1.5% by volume of RCFs were added to the cement composites. The reinforcing effect was most obvious with the addition of 1% by volume of RCFs, by which the flexural and compressive strengths were increased by 82% and 47%, respectively. This study revealed that RCFs have a great potential to be utilized as reinforcement into the cement composites.

Structural transformation and phase change properties of Se substituted GeTe

GeTe1−xSex (0 ≤ x ≤ 1.0) alloys have been prepared both in bulk and thin film forms to study the effect of selenium (Se) substitution for tellurium (Te) on the phase change properties. It is observed that with increasing Se substitution in GeTe, the structure transforms from rhombohdral structure to orthorhombic structure. Rietveld Refinement analysis support the phase transformation and show that the short and long bond lengths in crystalline GeTe decrease with increasing Se substitution but the rate of reduction of shorter bond length is more than the longer bond length. The GeTe1−xSex thin films undergo amorphous to crystalline phase change when annealed at high temperatures. The transition temperature shows an increasing trend with the Se substitution. The contrast in electrical resistivity between the amorphous and crystalline states is 104 for GeTe, and with the Se substitution, the contrast increases considerably to 106 for GeTe0.5Se0.5. Devices fabricated with thin films show that the threshold current decreases with the Se substitution indicating a reduction in the power required for WRITE operation. The present study shows that the crystalline structure, resistance, bandgap, transition temperature and threshold voltage of GeTe can be effectively controlled and tuned by the substitution of Te by Se, which is conducive for phase change memory applications.

Reduction of Water Vapor Permeability in Food Multilayer Biopackaging by Epitaxial Crystallization of Beeswax

In this paper, multilayer pectin-beeswax/colophony-pectin (P-BC-P) films including different proportions of beeswax/colophony mixtures were prepared in order to reduce the water vapor permeability. FTIR, XRD, DSC, polarized light microscopy (PLM), and water vapor permeation assays were performed. Characterization techniques showed (i) polar interactions between beeswax and colophony at the amorphous phase, (ii) changes in beeswax crystalline phase from sponge-like to needle-like structure, and (iii) formation of a eutectic mixture at BC3 70/30 ratio which guides the epitaxial crystallization of beeswax. Pure pectin films showed low resistance to the water vapor permeation (361 × 10−13 g m m−2 s−1 Pa−1), while multilayer films showed major control over the transport process. P-BC3-P showed one of the lowest water vapor permeability (WVP) values (56 × 10−13 g m m−2 s−1 Pa−1) and the closest WVP value to that of polyethylene films (LDPE 5.8 × 10−13 g m m−2 s−1 Pa−1). This result was attributed to the ordered crystalline structure reached by the epitaxial crystallization of beeswax within the hydrophobic phase.

Effect of limestone powder on mechanical strength, durability and drying shrinkage of alkali-activated slag pastes

The use of limestone powder (LSP) as a cement replacement is used in abundant applications due to its low cost and wide availability. Adversely, the use of LSP as a part of the precursors of alkali-activated materials (AAMs) is still in the developing stage. This scarcity of studies opened the door and encouraged the researchers for more investigations. Thus, this paper studied the effect of various amounts of LSP on some properties of alkali-activated slag (AAS) pastes activated with NaOH and Na2SiO3 solution. Slag was partially replaced with LSP at ratios of 15–60 wt%. The effects of LSP on mechanical strength, water absorption, chloride penetration permeability, drying shrinkage were studied. Advanced apparatuses were applied to detect the changes in crystalline phases, hydration products and microstructure of the pastes with and without the inclusion of LSP. The results confirmed that 15% LSP was the optimum amount, which is responsible for the highest mechanical strength, lowest water absorption and lowest charge passed. The drying shrinkage was mitigated with the inclusion of LSP. The inclusion of 15% LSP enhanced the 28-day compressive strength and flexural strength by 11.41% and 13.7%, respectively, while the water absorption, charge passed and drying shrinkage were decreased.

Calcination Temperature Effect in Catalyst Reactivity for the CO SELOX Reaction Using Perovskite-like LaBO3 (B: Mn, Fe, Co, Ni) Oxides

H2 production by conventional processes such as reforming reactions involves formation of some undesired products such as CO. Selective CO oxidation (SELOX) is a good alternative to reduce its concentration because it is a thermodynamically favorable process. Perovskite-like oxides (LaMO3) are used in this work to catalyze the CO-SELOX process and they were synthetized by the self-combustion method. All catalysts were calcined at different temperatures (400 °C–800 °C) to analyze its impact on the material physicochemical properties. Different analytical techniques were used to study changes in structural and chemical properties. Temperature-programmed reaction (TPRe), using CO oxidation and CO-SELOX, was used to measure the catalytic reactivity of perovskite-like oxides. It was found that catalytic activity decreases when calcination temperature (CT) increases and that is correlated with oxygen mobility, surface defects, and surface concentration of manganese or cobalt species. It is also found that there is a crystalline phase change in the solids when the CT increases from 500 to 600 °C. The high catalytic activity observed at low CT remained even if they were calcined below 600 °C, which implies the possibility of amorphous species having catalytic activity that do not require a well-structured perovskite.

Rhombohedral symmetry in GaAs1− x N x nanostructures

Nanocrystalline structures of GaAs1−x N x thin films were prepared on 7059 Corning glass substrates by means of an RF magnetron sputtering system using a GaAs target and N2 as ambient-gas, at several values of substrate temperature (T s). The range of T s was chosen from room temperature to 400 °C. The nitrogen concentration into the GaAsN layers is (1.0% ± 0.2%). The average energy band gap of the GaAsN nanostructures, calculated from their optical absorption spectra, is 2.9 ± 0.2 eV. The Raman scattering spectra exhibit vibrational modes associated to the rhombohedral phase due to the crystalline structural transformation from the zincblende (ZB)-GaAs caused by the introduction of N into the lattice. From x-ray diffraction (XRD) patterns the ZB structure was identified with two additional pairs of peaks which were associated to two types of cubic to rhombohedral crystalline phase changes of the material. One type has a low deformation to a moderately elongated unit cell, and the second type has a higher deformation to a more elongated unit cell. The rhombohedral symmetry of the crystalline lattice in the GaAsN nanostructures has been calculated from XRD data to confirm experimental evidences. The total average grain size was determined from the Scherrer formula: 3.3 ± 1.2 nm. The photoluminescence spectra are characterized by a very broad emission band which encompasses photon energies from near infrared to UV (775–310 nm, i.e. 1.6–4.0 eV).

The Long and Bright Path of a Lanthanide MOF: From Basics towards the Application.

The development of portable, reliable, and low-cost sensors for assessing the quality of natural water sources is of high relevance in developing countries as they can serve as an intermediate solution prior to the building of permanent potable water distribution infrastructure. These sensors should be simple to operate by non-trained operators and easy to manufacture locally. Lanthanide-based metal-organic frameworks (MOFs) offer a trustable platform due to their intense emission in regions of the visible spectra and their high sensitivity to fluorides in water. Cotton was chosen as a substrate due to its high hydrophilicity which, together with the highly porous nature of the MOF, allows for shorter reaction times. The modified cotton was characterized by XRD, SEM as well as XAFS, hence probing the presence of [Tb(BTC)6 (H2 O)] (Tb-BTC) attachment to cotton. Changes in the emission when Tb-BTC modified cotton was exposed to water and aqueous fluoride solutions were monitored as a function of time. Crystalline phase changes were identified that correlated to structural information. Finally, the Tb-BTC modified cotton was used to build a fluoride demonstrator sensor with a linear response of up to 10 mg L-1 and a limit of detection of 0.8 mg L-1 , making it suitable for drinking water analysis under international regulations.

Calcium aluminate cement in castable alumina: From hydrate bonding to the in situ formation of calcium hexaluminate

Calcium hexaluminate (CA6) is an intrinsically densification-resistant material, therefore, its porous structures are key materials for applications as high-temperature thermal insulators. This article reports on the combination of calcined alumina and calcium aluminate cement (CAC) in castable aqueous suspensions for the in situ production of porous CA6. The CAC content (10–34 vol%) and the curing conditions ensure structural integrity prior to sintering and maximize the development of hydrated phases. Changes in physical properties, crystalline phases, and microstructure were investigated after isothermal treatments (120–1500 °C), and three sequential porogenic events were observed. The hydration of CAC preserved the water-derived pores (up to 120 °C), and the dehydroxylation of CAC hydrates (250–700 °C) generated inter-particles pores. Moreover, the in situ expansive formation of CA2 and CA6 (900–1500 °C) hindered densification and generated intra-particle pores. Such events differed from those observed with other CaO sources, and resulted in significantly higher pores content and lower thermal conductivity.

Structural and TL glow curve of GdAlO3 perovskites

TL glow curve of any semiconductor is the patterns that mean when a material is suitable as Thermoluminescent (TL) material. Gadolinium aluminate (GdAlO3) perovskites have several properties that can be propose it as a good host for thermoluminiscent materials. GdAlO3 perovskite powder was synthesized by coprecipitation method and the powders were analyzed by characterization techniques. The Differential scanning calorimetry study showed changes in crystalline phases at 900 °C and 1084 °C during the calcination process. The first change of crystalline phase was identified by X rays diffractometry technique as a change from GdAlO3 hexagonal to GdAlO3 orthorhombic. TL glow curves of GdAlO3 under ultraviolet (UV) 256 nm and beta radiation effects were observed as crystallite size was increased.

Synthesis and characterisations of non-covalently bound aniline–indium(III) porphyrins

The aniline–indium(III) porphyrin chromophoric systems in which aniline is bonded non-covalently with porphyrin macrocycles were obtained by the treatment of each of the indium(III) porphyrins, i.e. tetra-p-methoxyphenyl indium(III) porphyrin and tetra-p-chlorophenyl indium(III) porphyrin with neutral aniline in CHCl3/CH3OH mixtures. The prepared aniline–indium(III) porphyrin chromophoric systems were successfully characterised by using FT-IR spectroscopy, 1H NMR spectroscopy and ESI-mass spectrometry. The 1H NMR and UV–Visible absorption spectroscopic studies of aniline–indium(III) porphyrin systems were further recorded as a function of pure aniline concentration in proper solvents. The results of these spectroscopic studies indicate the existence of interchromophoric interactions between aniline and indium(III) porphyrins which increase with the increase in pure aniline concentrations. Powder X-ray diffraction (PXRD) measurement data reflects change in crystalline phases of parent complexes upon incorporation of aniline molecules. Thermogravimetric analysis (TGA) indicates that aniline-incorporated indium(III) porphyrins are less thermally stable than their parent complexes.

Thermal management on external surfaces by thermochromic materials

Thermochromism is the property of a substance to change colour when subjected to a change in temperature. Generally, the custom activation temperature is around −10 °C to 69 °C. Thermochromism doesn't always need to be a change between two colours, but it can also change from colour to transparent. The material which has thermochromism property is used as thermochromic material, and it is also known as heat-sensitive colour change material. The colour transition occurs due to change in crystalline phase and structure when exposed to different temperature conditions. These thermochromic materials are mainly used as temperature indicators in many industrial sectors and utilized to impart heat control and colour changing abilities to windows, exterior walls and other construction components, like the rate of heat embrace by the surface of a vehicle can be applied by thermochromic material coating. By reducing the heat embracement by surface, it can endure the battery performance. This paper gives us a brief idea about the usage and impact of thermochromic material in electric vehicles.

Stress-Induced In Situ Modification of Transition Temperature in VO2 Films Capped by Chalcogenide.

We attempted to modify the monoclinic–rutile structural phase transition temperature (Ttr) of a VO2 thin film in situ through stress caused by amorphous–crystalline phase change of a chalcogenide layer on it. VO2 films on C- or R-plane Al2O3 substrates were capped by Ge2Sb2Te5 (GST) films by means of rf magnetron sputtering. Ttr of the VO2 layer was evaluated through temperature-controlled measurements of optical reflection intensity and electrical resistance. Crystallization of the GST capping layer was accompanied by a significant drop in Ttr of the VO2 layer underneath, either with or without a SiNx diffusion barrier layer between the two. The shift of Ttr was by ~30 °C for a GST/VO2 bilayered sample with thicknesses of 200/30 nm, and was by ~6 °C for a GST/SiNx/VO2 trilayered sample of 200/10/6 nm. The lowering of Ttr was most probably caused by the volume reduction in GST during the amorphous–crystalline phase change. The stress-induced in in situ modification of Ttr in VO2 films could pave the way for the application of nonvolatile changes of optical properties in optoelectronic devices.

Thermal Silicidation of Ni/SiGe and Characterization of Resulting Silicide Films Using Raman Spectroscopy and X-ray Diffraction

For advanced application specific devices, combinations of Si/Ge, Ge/Si, Si1-xGex/Si are frequently introduced in the device fabrication process. Epitaxy, condensation and annealing processes are commonly used for controlling the Ge content to a desired level. Strain and crystallinity can be affected by a small variation in composition or Ge content, which can result in device performance deterioration or failure. Thus, the composition, strain and crystallinity must be carefully monitored and controlled throughout the manufacturing process. The electrode formation process is also very critical for successful device fabrication. Any spikes and/or electrically active defects near junctions can be fatal to the device yield. Silicidation processes and resulting silicides must be investigated as much as possible using various non-invasive material characterization techniques.In this study, we report the thermal silicidation characteristics of Ni/Si1-xGex with various Ge content under different annealing temperatures in the range of 225oC ~ 400oC in N2 ambient. Thermal silicidation was performed in a stacked hotplate-based SAO-302LP system designed for 300mm wafers. For resulting silicide characterization, measurements of sheet resistance, Raman spectra, X-ray diffraction curves as well as scanning electron microscopy (SEM) observations were performed. We have studied Ge content and annealing temperature dependence on the resulting electrical and crystallographic silicide characteristics.Figure 1 shows 647nm excited Raman spectra and X-ray diffraction (XRD) curves from reference Si, and resulting silicide from Ni/Si0.75Ge0.25 before and after annealing under at 235oC, 310oC and 400oC.Raman spectra and sheet resistance measurements showed silicide formation and silicide layer thickening with increasing annealing temperature. XRD curves clearly indicated the change of crystalline phase of resulting silicide with annealing temperature increase. Various aspects of thermal silicidation and its characterization will be discussed at the conference. Figure 1

Proposal for a universal nonvolatile logic device based on the phase change magnetic material

Memory devices that are capable of logic functions have shown great potential in constructing non-von Neumann parallel computing architecture. Here, we proposed a universal nonvolatile logic device, utilizing the amorphous–crystalline phase transition behavior and phase change control of ferromagnetism property of Mn-doped GeTe phase change magnetic material (PCMM). The materials implication (IMP) logic in one step and sequential NAND logic were presented theoretically, based on which the functional completeness of Boolean logic could be realized. The logic operating results can be stored directly in the residual magnetization of the PCMM. This proposal may promote the design and future experimental implementation of next generation electromagnetic devices for data storage and computing.

Thermal Analysis of Ca<sub>1+<i>x</i></sub>Cu<sub>3</sub>Ti<sub>4</sub>O<sub>12+<i>x</i></sub> Precursor in Nitrogen and Oxygen Environment at 1000 °C

The thermal kinetic analyses are prepared on Ca1+xCu3Ti4O12+x powders using simultaneous thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) measurement in a dual atmospheric gases environment. Initially, the nitrogen gas flowed from room temperature to 1000 °C, and then the environment was shifted and hold for 1 hour with oxygen. The result shows that the TGA patterns of the temperature and mass loss are disorderly with x values. The mass loss % patterns slightly decreased with increased additional Ca-based element. The decreased of oxygen absorption as the values of x increased also can be explained by the reduction of single-phase CCTO structure when excess Ca ions. The DSC pattern shows two prominent endothermic peaks and two exothermic peaks that relate to the melting point of the reactant and crystalline phase changes of samples, while the significant endothermic peak at 1000 °C is corresponding to the formation of CCTO compounds as identified by XRD analysis.

Thermally induced structural organization of nanodiscs by coarse-grained molecular dynamics simulations

Membrane scaffold proteins (MSP) nanodiscs have been extensively used in structural study of membrane proteins. In cryo-EM, an incorporation of target proteins into nanodiscs is conducted under a rapid change from cryogenic to ambient temperatures. We present a coarse-grained molecular dynamics (CGMD) study for investigating an effect of temperature on the structural organization of DPPC-nanodisc and POPC-nanodisc. A non-monotonic response of physical quantities (i.e. the lipid order parameter, nanodisc flatness, structural change, solvation property, radius of gyration) with increase in temperature (T = 200–350 K) is found to be associated with the gel-ripple-liquid crystalline phase change within nanodiscs. The reorganization of lipids upon temperature variation induced conformational changes of MSP to minimize hydrophobic exposure of the lipid membrane to an aqueous environment. Structural response to temperature is different to a certain extent between the saturated DPPC and unsaturated POPC.

Effects of nozzle-to-substrate distance and annealing atmospheres on V2O5 thin films prepared by spray pyrolysis technique

In this research, vanadium pentoxide (V2O5) thin films were prepared on glass substrates by spray pyrolysis technique and the effect of nozzle to substrate distance (NSD) was investigated. The field emission Scanning electron microscope (FESEM) images and EDX analysis indicated the formation of nano-grains that improved their stoichiometry with increasing NSD. The XRD and Raman spectra showed that structural properties (orthorhombic/tetragonal phases) depend on NSD. The analysis of optical transmittance spectra revealed that with increasing NSD the direct band gap of the samples is increased from 2.27 to 2.60 eV due to improvement of chemical stoichiometry and crystalline phase change of the layers. Finally, sample with weak tetragonal phase was annealed in various atmospheres (N2, air and O2). We found the atmosphere of annealing process had profound effect on morphological, structural and optical properties of the as-grown sample.