Phase Formation Mechanism Research Articles

Temperature-Time profile effects on evolution of physical and electronic properties in visible light Cu2CoSnS4 photodetectors

Earth-abundant quaternary chalcogenide Cu2CoSnS4 (CCTS) films on soda-lime glass (SLG) substrates are prepared via non-vacuum, cost-effective direct solution spin coating technique. The phase formation mechanism of CCTS films is investigated via TGA, FTIR, XRD, and RAMAN characterization. Annealing temperature effects on the crystalline phase, chemical composition, and grain growth, strongly linked with electrical and photodetection parameters of CCTS films, are systematically investigated through XRD, Raman, FEG-SEM, and EDS analysis. Through the transfer length measurement (TLM) method, the electrical properties of CCTS films annealed at 575 °C exhibit noticeable 92% reduction of both contact resistance (Rc) and resistivity (ρ), compared to those of the film processed at 300 °C. The highest photoresponsivity (7.50 A/W) and specific detectivity (4.70 × 1010 Jones) of CCTS devices have been demonstrated with annealing conditions at 575 °C and a bias voltage of 10 V as well. The present study reveals the impact of both annealing temperature and bias voltage on photodetector performance.

Amphiphilic copolymer aqueous solutions with cholinium ionic liquids as adjuvants: New insights into determination of binodal curves and phase-separation mechanisms

Aqueous two-phase micellar systems (ATPMS) are more than simple amphiphilic copolymer or surfactant aqueous solutions since due to the formation of biphasic regimes, at certain temperatures, these can be successfully used for the separation, encapsulation, and formulation of several bio-based compounds. The recent use of ionic liquids (ILs) as adjuvants in the formation of ATPMS have enlarged its “working window”, but the measurement of respective binodal curves is still very empiric and dependent of operator accuracy through the visual determination of cloud-point temperature. In this work, the range of ATPMS using ILs as adjuvants was extended, providing more insights about their phase formation mechanisms, as well as into determination of cloud-point values of the lower critical solution temperature (LCST)-type demixing transition by using the new temperature modulated optical refractometry approach. The binodal curves of ATPMS composed of Pluronic® L35/PBS buffer at pH 7.4 + cholinium ILs were determined, by using two different methods, i.e.: cloud-point temperature (TCP) visual determination versus temperature modulated optical refractometry (TMOR). TMOR method was more sensitive to the determination of biphasic transition, particularly, in highly diluted solutions (< 3.0 wt% of Pluronic L35). The results also established that the addition of cholinium ILs decreased significantly the phase separation temperatures of Pluronic L35/PBS, with an increase of biphasic region (viz. lower of TCP values) as a function of the relative hydrophobicity of the IL anion, i.e.: [Hex]− > [But]− > [Pro]− > [Ac]− > Cl−. The use of cholinium ILs as adjuvants is particularly important to provide mild conditions for ATPMS-based separation and encapsulation strategies, while TMOR-based methods allow an improvement of phase separation determination accuracy.

Structure and properties of MoSi2–MeB2–SiC (Me = Zr, Hf) ceramics produced by combination of SHS and HP techniques

Composites MoSi2–ZrB2–SiC and MoSi2–HfB2–SiC were investigated in this study as the prospective materials for high-temperature industrial heaters. The composites with relative density 97–98% were produced by combustion synthesis followed by hot pressing. The macrokinetic features of combustion, as well as phase and structure formation mechanisms in the combustion waves, were analyzed and their influence on the structure, mechanical properties, and performance of heaters were ascertained. The mechanical and electrical properties of the heating elements produced in this work are considerably higher as compared to conventional MoSi2 counterparts. Among the investigated compositions, the MoSi2–HfB2–SiC demonstrated the highest resistance to high-temperature oxidation. Both compositions featured the formation of a stable continuous oxide layer consisting of crystalline α-quartz (high-temperature modification of SiO2) reinforced by ZrO2, ZrSiO4, HfO2, and HfSiO4 precipitates.

Production of nanostructure Zr–ZrCr2–Cr composite via MA process and subsequent heat treatment

ABSTRACT In this study, the nanophase ZrCr2 intermetallic compound was produced by the mechanical alloying (MA) and subsequent heat treatment. The phase transformations, crystallite size, lattice strain, and stored energy were studied at different milling times. The results indicated that MA caused to form a nanocomposite of the Cr(Zr) and Zr(Cr) supersaturated solid solutions. After 32 h of milling, the stored energy of Cr-reach phase in the powder mixtures reached to about 7.407 kJ/mol. Also, the 32 h milled powders were heated up to 750°C by the differential thermal analysis in argon atmosphere which the XRD results of the heated powders revealed that the nanostructure ZrCr2 intermetallic compound was formed in the Zr and Cr matrix. Indeed, MA reduced the formation temperature of the ZrCr2 intermetallic phase from 1673 °C to 608 °C which confirmed that MA and subsequent heating is a proper technique at low temperatures. In addition, a kinetics analysis implied that the Johnson-Mehl-Avrami (JMA) model can explain the kinetics formation of ZrCr2 phase during the heat treatment which confirmed that the dominant mechanism of the intermetallic phase formation was the process controlled by the volume diffusion phenomenon, so that the nuclei grow in three dimensions of space.

Cu/(Co+Sn) ratio effects on physical and photodetective properties for visible light absorbing Cu2CoSnS4 nanoparticles via a one-pot hydrothermal process

The composition ratio plays a vital role in modulating the thermal, magnetic, and optoelectronic properties of earth-abundant quaternary chalcogenides. Here we report on an impact of Cu/(Co + Sn) ratio on secondary phase formation, size, and shape of Cu2CoSnS4 (CCTS) nanoparticles synthesized via monoethanolamine (MEA) promoted the hydrothermal process. The CCTS phase formation mechanism is experimentally elucidated by a time-dependent synthesis study during a one-pot facile hydrothermal reaction, and it is confirmed by using X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) analysis. The morphology, particle size distribution, and shape of synthesized nanoparticles are examined by field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) analysis. The N-Methyl-2-pyrrolidone (NMP) solvent-based CCTS paste was drop-casted on a thermally oxidized silicon wafer (∼100 nm SiO2) to form films. The increase in optical bandgap from 1.48 eV to 2.00 eV is observed for an increase in Cu/(Co + Sn)) ratio of prepared CCTS films. The electrical, photodetection properties of the prepared films with respect to the (Cu/(Co + Sn)) ratio under dark and light illumination are studied. The lowest sheet resistance (Rsh= (13.56 ± 0.9) × 103 Ω/cm) and contact resistance (Rc= (108.31 ± 3.43) × 103 Ω) is obtained for devices made with a higher value of Cu/(Co + Sn) ratio = 1.17. On the other hand, the highest photosensitivity (Sph = 32%), photoresponsivity (Rph = 75.58 mA/W), and detectivity (Dph = 1.44 × 108 Jones) are demonstrated for device assembled with the lowest ratio (∼0.86) of Cu/(Co + Sn). The present study reveals that Cu/(Co + Sn) ratio affects a significant impact on such as a phase, morphology, chemical compositional ratio of nanoparticles, optical, electrical, and photoresponsive properties of prepared films.

Synthesis features, structure and properties of promising high-temperature ceramics in the Hf-Ta-B-Ti-Si system

The study covers the elemental synthesis features of Hf-Ta-B-Ti-Si ceramic materials used to obtain promising high-temperature ceramics and analyze its structure and properties. The macrokinetics of self-propagating high-temperature synthesis (SHS) were studied. Combustion temperature and velocity as a function of initial temperature were plotted. It was established that chemical interactions occurring in the liquid phase play a pivotal role in the combustion process. Structure and phase formation processes were studied using the stopped combustion front technique. The mechanism of phase formation in the combustion wave was determined. The primary crystals of hafnium, titanium and tantalum diborides are precipitated from the super-saturated melt after the Si and Ti contact melting and B, Hf and Ta dissolution in the melt through the reactive diffusion process. A two-phase structure consisting of complex solid solutions based on diboride and borosilicide is formed due to the similarity of the crystal lattices. Porous synthesis products of the specified composition were milled into powders with the required particle size distribution for subsequent hot pressing (HP) or spark plasma sintering (SPS). It was found that specimens produced by HP, SPS, and SHS pressing feature a similar phase composition containing solid solutions based on diboride (Hf,Ti,Ta)B 2 and borosilicide (Hf,Ti,Ta) 5 Si 3 B. Specimens were made of ceramics produced using the above technologies for physical-mechanical testing. It was found that the hardness and elastic modulus of (Hf,Ti,Ta)B 2 solid solution are 2-3 times higher than that of (Hf,Ti,Ta) 5 Si 3 B borosilicide. Depending on composition, the density of ceramics produced varied from 8 to 6.5 g/cm 3 , which corresponds to a porosity of less than 5 %. Temperature dependences of heat capacity and diffusivity were determined. The heat conductivity of ceramics produced by HP and SPS was 24.05 and 23.1 W/(m•K), respectively.

Reductive roasting mechanism of copper slag and nickel laterite for Fe-Ni-Cu alloy production

Direct reduction-magnetic separation process (DRMSP) is a highly effective and clean method to upgrade the complex resources, which has been widely used to recovery the value metals in copper slag (CS) and nickel laterite (NL) in recent years. Adequate growth of the alloy particles is a key parameter influencing the complete extraction of alloys from CS and NL in this process. Therefore, the liquid phase formation mechanism, growth kinetics of the alloy particles, and the correlation between the alloy particle growth and liquid phase formation were studied to reveal the synergistic effect of the co-reduction of CS and NL. The results indicated that fayalite in the copper slag reacted with forsterite in nickel laterite to form augite group minerals with low melting points, resulting in more liquid phase formation in the reductive roasting process. A comparison with the reduction kinetic parameters of the single nickel laterite showed that the growth index and activation energy decreased significantly from 2.85 and 272.98 KJ/mol to 2.08 and 171.99 KJ/mol, respectively, after the addition of 40% copper slag, which confirmed that copper slag promoted the particle growth. Moreover, the liquid phase increased the total cohesive force between the alloy particles, revealing the correlation between alloy particle growth and liquid phase.

Development of phases in the sol-gel derived mixed-metal-oxide (Al2O3–TiO2–ZnO) functional sorbent material

Aluminium-Titanium–Zinc mixed-metal-oxide system was investigated in order to elucidate appropriate sorbent material for the High-Temperature Gas-Desulphurisation (HTGD) in the Integrated Gasification Combined Cycle (IGCC). Conceptually, Zn-based constituent phases support sorption functionality, Ti-based constituent phases support chemical stability and Al-based constituent phases support mechanical durability. Samples were prepared using sol-gel synthesis in a broad compositional range from gahnite to Zn-titanate spinel; i.e. gahnite was Ti-doped on the account of Al (0–100%). Complexing agent was used to control the hydrolysis rate. We monitored the thermal and structural evolution in order to observe and clarify different mechanisms of phase formation, as a function of the doping and temperature conditions. The significance of this work lies within insight in the stability ranges of the observed solid-solutions, whereas gahnite spinel and zinc titanate spinels can interchange cations only in limited amounts, depending on the conditions, as confirmed from the structure refinement. It was observed that these solid-solution phases exhibit quite different stability when thermally treated. More importantly, observed partial phase-separation at low-temperature thermal treatment (which occur on behalf of different hygroscopic properties of the (Al,Ti)–Zn gels) significantly precludes the mechanisms of phase development at high-temperatures. Thereof, intermediate Zn-based phase was found to be responsible for the facilitated early zincite crystallisation. Microstructural and textural changes were correlated according to structural changes. Characterisation results allowed understanding of compositional and treatment conditions necessary for the selection of sorbent best with best functionality.

Structure and Phase Formation Mechanism for Hollow Spheres of Aluminum-Magnesia Spinel in Obtaining Powders by Chemical Dispersion of Aluminum-Magnesium Alloys

The results of an investigation of the processes underlying the formation of hollow aluminum-magnesia microspheres by chemical dispersion of magnesium-aluminum alloys with heightened content of magnesium are reported. The mechanism of the formation of microspheres and the factors determining their structural features and sizes are elaborated. It is shown that magnesium additives influence the formation of the structure of hollow microspheres and their number. The fine structure of the powders before and after heat-treatment was studied.

Granulation Effect Analysis of Gas Quenching Blast Furnace Slag with Different Basicities

High content amorphous phase blast furnace slag beads were prepared by gas quenching blast furnace slag (BFS), which could not only avoid a series of environmental problems caused by traditional water quenching methods, but also significantly increase the added value of BFS subsequent products. In this paper, the granulation mechanism of BFS and the amorphous phase formation mechanism of slag beads were studied by combining the physical properties of BFS and the granulation effect. The results showed that the viscosity of BFS decreased with the increase of basicity; the bigger the basicity, the higher the bead formation rate, the smaller the particle size and the more regular the slag shape. The smaller the basicity, the greater the crystallization activation energy and the smaller the Avrami exponent, which indicated that the crystal was more difficult to nucleate and grow. The increase of the cooling rate could effectively inhibit crystal precipitation. Therefore, the high basicity and cooling rate could not only guarantee the high bead formation rate of BFS, but also ensure the high content amorphous phase of slag beads.

Influence of divalent metals (Zn, Cu and Co) on the synthesis and magnetic properties of spinel ferrite nanopowders

Hematite iron oxide (α-Fe2O3) and spinel ferrite nanopowders were synthesized by hydrothermal technique. The spinel ferrite MFe2O4 is prepared using three divalent metals M = Cu, Zn and Co. In order to investigate the spinel phase formation mechanism, we have used two atomic ratios (M/Fe) between Fe and divalent metal (above and below the stoichiometric ratio) and two preparation times (6 and 10 h). The nanopowder structure and morphology were characterized by mean of X-ray diffraction, scanning and transmission electron microscopies observation. The magnetic properties of the powder were archived using vibrating sample magnetometer. The results reveal that using low divalent metallic concentration yields to a powder composed of hematite and spinel phases. However, increasing the divalent metal concentration leads to the formation of monophasic spinel powder with a metallic oxide secondary phase. The spinel phase formation enthalpy controls the powder crystallite size and the secondary phase formation. The magnetic properties of the powder are altered by the presence of secondary phase. The magnetic exchange between the phase causes the surface spin canting resulting in the magnetic properties deterioration.

Features of Au(80)Sn(20) thin film solder manufacturing technology

This work provides the results of manufacturing technology development for Au(80)Sn(20) thin film solders produced with electron-beam evaporation coating of alternating gold and tin layers. The phase formation mechanism in the produced solders was studied to work out an evaporation procedure which enables to make a solder with the properties meeting the requirements to soldering of a laser diode onto a heatsink base surface.

DFT – Driven design of hierarchically structured, strong and highly conductive alloys in Cu–Ti system via in situ hydration - re-oxidation

To engineer a Cu–Ti based alloy with titanium-and oxygen-free copper matrix using commercially-feasible powders, an in situ hydrogenation – re-oxidation approach was suggested and supported by grand potential diagram mapping of Cu–Ti–O–H system. Reactive composite powders with nominal composition Cu–10%TiH2, containing 7% native Cu2O, were manufactured by high energy ball milling. The phase and structure formation mechanisms were experimentally investigated by DSC, in situ XRD, SEM, and HRTEM.

Effect of Post-Annealing on the Phase Transformation and Critical Current Density of (Bi, Pb)-2223/AgAu Tapes

During the sintering process of Ag-alloy sheathed Bi-2223 tapes, post-annealing (PA) played an important role on the final current capacity by forming a Pb-rich phase named (Pb,Bi)3Sr2Ca2CuOx (3221) and healing the cracks. Due to the different oxygen penetration rate between AgAu alloy and pure Ag, which is traditionally used in other Bi-2223 tapes, the influence of PA parameters on the 3221 phase content, microstructures, and current capacity of AgAu tapes should be systematically studied. In this study, PA processes with different temperatures of 770–800 °C have been performed on fully reacted 37-filamentary (Bi, Pb)-2223/AgAu tapes in the atmosphere of 7.5% O2 balanced with Ar. It is found that the 3221 phase appeared after PA with its amount first increasing then decreasing with increasing PA temperature. The critical temperature Tc and peak temperature (Tp) obtained with AC susceptibility measurement both increased with increasing PA temperature, and reached the maximum value at 780 °C then decreased with increasing PA temperature. Due to the improvement of Tc and intergrain connectivity, the critical current density (Jc) increased by 24% after PA at 780 °C. Meanwhile, the 3221 phase formation mechanism has also been systematically discussed by varying the amount of remnant liquid in tapes in HT1 process.

Microstructure formation and electrical resistivity behavior of rapidly solidified Cu-Fe-Zr immiscible alloys

The immiscible Cu-Fe alloy was characterized by a metastable miscibility gap. With the addition element Zr, the miscibility gap can be extended into the Cu-Fe-Zr ternary system. The effect of the atomic ratio of Cu to Fe and Zr content on the behavior of liquid-liquid phase separation was studied. The results show that liquid-liquid phase separation into Cu-rich and Fe-rich liquids took place in the as-quenched Cu-Fe-Zr alloy. A glassy structure with nanoscale phase separation was obtained in the as-quenched (Cu0.5Fe0.5)40Zr60 alloy sample, exhibiting a homogeneous distribution of glassy Cu-rich nanoparticles in glassy Fe-rich matrix. The microstructural evolution and the competitive mechanism of phase formation in the rapidly solidified Cu-Fe-Zr system were discussed in detail. Moreover, the electrical property of the as-quenched Cu-Fe-Zr alloy samples was examined. It displays an abnormal change of electrical resistivity upon temperature in the nanoscale-phase-separation metallic glass. The crystallization behavior of such metallic glass has been discussed.

Ti–TiB2 composites consolidated by spark plasma sintering: Reaction mechanism, characteristics of in-situ formed phases and densification behavior

Titanium matrix composites containing 4.8 wt. % TiB2 admixed powder were processed by spark plasma sintering at a temperature range of 750–1350 °C for a dwell time of 5 min under an external pressure of 50 MPa in vacuum. The effects of sintering temperature on densification behavior and microstructural evolution were studied, with special attention and emphasis on researching the mechanisms of TiB phase formation. Microstructures of the composites were examined by means of optical microscopy (OM) and scanning electron microscopy (SEM). X-ray diffraction (XRD) patterns and micrographs investigation confirm that sintering temperatures above 900 °C are needed for creating the TiB phase through the in situ reaction between Ti and TiB2. The results also show that, along with promoting densification and progress of the Ti/TiB2 reaction, particle fragmentation occurs in contact surfaces between reinforcement and titanium particles during the sintering process. The fracture surfaces of composites exhibit few characteristics of TiB pull-out and particle debonding which indicates that the in-situ formed TiB phases are well bonded to the Ti matrix to transfer load from the matrix to reinforcements. Furthermore, quantitative analysis of the existing phases demonstrates that the reaction between Ti and TiB2 is fairly complete at higher sintering temperature.

The influence of phase formation routes on the microstructure and critical current density of Nb3Al superconductor prepared by mechanical alloying and subsequent sintering

The phase formation mechanism, microstructure and superconducting properties of Nb3Al prepared by mechanical alloying and subsequent sintering were systematically investigated in this work. It was found that when the milling time is less than 16h, the Nb3Al is formed via the reaction between the Nb2Al that crystallizes from Nb–Al amorphous phase and residual Nb during subsequent sintering process. Whereas the milling time exceeds 16h, the Nb3Al transforms directly from Nb–Al supersaturated solid solution (Nb(Al)ss) during subsequent sintering process. Due to this difference in phase formation route, the grain size of M16h sintered sample is larger than that of M12h and M20h sintered samples. Besides, the intergranular connectivity of M16h sintered sample is the poorest among them. These factors make the critical current density (Jc) of M16h sample abnormally lower than that of both M12h and M20h samples. According to these results, the highest Jc (about 1 × 104 A cm−2 at 4.2K, 6T) is obtained for the sample prepared by 20h ball milling and subsequent sintering at 850°Cfor 5h.

Combustion synthesis of SiC-based ceramics reinforced by discrete carbon fibers with in situ grown SiC nanowires

This study proposes a combustion-based ceramic matrix composite processing technique intended on single-step in situ deposition of single-crystal SiC nanowires (SiCnw) on the surface of carbon fibers (Cf) and formation of SiCnw–reinforced SiC matrix. This was accomplished by Ta-catalyzed combustion of poly-(C2F4)-containing reactive mixtures with pre-mixed chopped Cf. Depending on the combustion conditions, carbon fiber surface is subjected either to formation of diffusion layers, ceramic particle incrustation or growth of continuous arrays of carbon-coated single-crystal SiCnw with a nearly defect-free lattice, 10–50 nm diameter and 15–20 μm length. Thermodynamics, phase and structure formation mechanisms are explored, and the optimal conditions are outlined for reproducible Cf/in situ SiCnw dual reinforcement of SiC-based ceramics. Hot pressing at 1500 °C produced Cf/in situ SiCnw-reinforced ceramic SiC–TaSi2 specimens with a relative density of 97%, 19 GPa Vickers hardness, 3-point flexural strength σ = 420 ± 70 MPa and fracture toughness K1C = 12.5 MPa m1/2.

A comprehensive study on the mechanism of ferroelectric phase formation in hafnia-zirconia nanolaminates and superlattices

Many applications, most notably memory and optical devices use ferroelectric materials. For many years the evolution of the field has revolved around understanding the materials science behind complex structures like artificial superlattices based mainly on perovskite-structure oxides. The recent discovery of ferroelectricity in fluorite-structure oxides has opened a new research direction. However, the formation of unstable or metastable phases in atomic layer deposited fluorite oxides has inhibited a full understanding of the origin of ferroelectricity in these materials. This work reports a comprehensive study of the structural and electrical properties of HfO2 and ZrO2 nanolaminates and superlattices of various layering combinations and thicknesses. The structural investigations provide insight into how to optimize conditions during atomic layer deposition to avoid the formation of unstable phases. Investigations showed that the starting layer of the material, the thickness ratio between HfO2 and ZrO2 layers, and the single-layer thickness strongly effected the ferroelectric properties. The influence of single-layer thickness related most strongly to the presence of interfacial nonferroelectric layers between the HfO2 and ZrO2 deposits. These features make the structures highly promising candidates for next-generation memory applications. Potentially other fluorite-structure oxides might also function as building blocks for nanolaminates and superlattices.

Phase selection and microstructure of slowly solidified Al-Cu-Fe alloys

The search for effective methods to fabricate bulk single-phase quasicrystalline Al-Cu-Fe alloys is currently an important task. Crucial to solving this problem is to understand the mechanisms of phase formation in this system. Here we study the crystallization sequence during solidification as well as the conditions of solid phase formation in slowly solidified Al-Cu-Fe alloys in a wide range of compositions. We have also constructed concentration dependencies of undercoolability by differential thermal analysis method. These experimental results are compared with data on chemical short-range order in the liquid state determined from ab initio molecular dynamic simulations. We observe that the main features of interatomic interaction in the Al-Cu-Fe alloys are similar for both liquid and solid states and they change in the vicinity of i-phase composition. In the concentration region, where the i-phase is formed from the melt, both the undercoolability and the crystallization character depend on the temperature of the melts before cooling.