Papers by Keyword: Phase Transition

Abstract: Based on the analysis of the defect formation in silicon carbide polytypes in different semiconductor manufacturing processing steps, device operation and environmental-device interaction it is concluded that external material and energy fluxes are generally able to destabilize the polytype structure. The governing reason is the formation of stacking faults and instabilities of the partial dislocation associated with them. A new ansatz is proposed to describe the structural instabilities using none-equilibrium thermodynamics and the entropy production. A criterial form for polyype transitions is proposed. The developed criterial form is applied to describe observed structural instabilities occur­ring under different external actions.

Abstract: Doping CZTS (copper-zinc-tin-sulfide) by replacing zinc with cadmium atoms is a crucial process for improving its electrical and optical properties. The primary goal is to modify the bandgap and increase the electrical conductivity of the material to enhance its efficiency in solar cell applications. This substitution induces a phase transition in the crystal structure from kesterite (favorable for zinc) to stannite (stable for cadmium). Experimental results showed that the pure sample (x = 0) was unstable, with a large dispersion in the conductivity measurements. Adding cadmium at a low ratio (x = 0.01225) improved the stability of the measurements while the conductivity decreased to ~10 S/m due to distortion stress in the crystal lattice. Increasing the ratio to x = 0.0269 resulted in a dramatic jump in the conductivity (~56 S/m) which is an indication of the onset of the phase transition. A computer code based on the K-Means algorithm was used to analyze the dispersion of measurements and isolated the most statistically reliable group.

Abstract: At temperatures of 290 K and 77 K, the phase composition and mechanical properties ofnonequiatomic medium-entropy (MEA) alloys Fe40Mn40Co10Cr10 and Fe50Mn30Co10Cr10 werecompared in the coarse-grained (CG) and nanostructured (NS) states, in which additionaldeformation mechanisms are activated under load: phase transformations in the MEAFe50Mn30Co10Cr10 (MEA TRIP) and twinning in the MEA Fe40Mn40Co10Cr10 alloy (MEA TWIP). Itis shown that in the NS state in both alloys, in contrast to the CG state, a complete phase transitionfrom the fcc to the hcp phase is observed, the content of which weakly depends on the temperatureand the number of torsion revolutions during high-pressure torsion (HPT). The transition from theCG to the NS state leads to an increase in the microhardness (in the NS MEA TWIP by 3.7 and inthe NS MEA TRIP by 2.25). In the CG state, a thermally activated character of plastic deformationis observed for both alloys in the temperature range of 290 – 77 K. In the NS state, MEA TWIPremains plastic under active compression deformation at 290 K and 77 K, whereas in NS MEATRIP under similar conditions, macroscopic plasticity is absent. Tensile deformation up to 50 % at30 K in the CG state for both alloys leads to a significant decrease in the absolute values of Young'smodulus over the entire temperature range.

Abstract: The multi-layered MoS₂ with alkali metal intercalation was prepared on the transparent conductor by the sulfurization of MoO₃, followed by the subsequent electrochemical sodiation process. The layered structure of MoS₂ could endow the efficient electron/ion transport pathways for fast charge transfer. Together with the good ion storage and conductive behavior, the MoS₂ pursues its potential in electrochemical applications.

Abstract: We developed a new 1-12-type magnetic material of (Sm,Zr)(Fe,Co)_11.3Ti_0.7 composition that exhibits magnetic properties superior to Nd-Fe-B magnets. In the new 1-12 magnets, the amorphous alloys of above composition show a change in XRD pattern with increasing of heat treatment temperature from a single 1-9 phase to 1-9 and 1-12 mixed phases, and finally to a single 1-12 phase, and the magnetic properties also change accordingly. In this study, we established a method for calculating the formation ratio of the 1-12 phase in the samples from the peak shift of the diffraction peaks of the 1-12 phase base on the peaks of the 1-9 phase. As a result, it was revealed that the formation ratio of the 1-12 phase in the samples, whose XRD pattern of 1-9 and 1-12 mixed phase, has a wide distribution, ranging from about 20 to 80 %. With the development of the phase transition from 1-9 to 1-12 phases, the lattice constant a of 1-12 phase increases, and inversely the lattice constant c of 1-12 phase decreases. Furthermore, it was revealed that the formation ratio of the 1-12 phase was about 83 % for the sample indicating the maximum coercivity H_c = 5.46 kOe.

Abstract: The structure, microstructure, Fourier transformed infrared spectra, dielectric, and impact generated energy harvesting characteristics of x(Ba_0.7Ca_0.3)TiO₃–(1-x)Ba (Zr_0.2Ti_0.8)O₃; x = 0, 0.5, and 1.0 synthesized using solid-state reaction method are discussed in this work. The X-ray diffraction (XRD) process was used to examine the forming of a single-phase compound. The Rietveld refinements of XRD data were used in FullProf software to determine crystal symmetry, lattice parameters, and space groups. A scanning electron microscope was taken into use to examine the surface morphology of all of the samples. The samples' phase transition temperature was observed to lie between-10°C and 87°C, shifting toward the higher temperature side as x increased. In the case of x = 0.5, two-phase transitions were discovered at 22°C and 70°C. The value of impact generated output voltage and electrical energy increases as applied mechanical energy increases. The findings of this study point to the possibility of using 0.5(Ba_0.7Ca_0.3)TiO₃–0.5Ba (Zr_0.2Ti_0.8)O₃ ceramic for energy harvesting and sensing purposes.

Abstract: An alternative low thermal budget silicon carbide syntheses route is presented. The method is based on self-propagating high-temperature synthesis of binary silicon-carbon-based reactive mul­tilayers. With this technique, it is possible to obtain cubic polycrystalline silicon carbide at relatively low annealing temperatures by a solid state reaction. The reaction starts above 600 °C. The transformation process proceeds in a four-step process. The reaction enthalpy was determined to be (-70 ± 4) kJ/mol.

Abstract: The evolution of the steel structure under thermocyclic action is considered. The possibility of increasing the complex of mechanical properties of steels after thermocyclic treatment is shown.

Abstract: We reported the structural, magnetic and magenetocaloric properties of Mn_1.25Fe_0.75P_{0. 50}Si_0.50B_x (x = 0.01, 0.02 and 0.04) X-ray diffraction patterns show that all compounds crystallize in the hexagonal Fe₂P-type crystal structure. Lattice parameter a increases while c decreases with increasing B contents. The Curie temperature of the compounds have been determined, the values are 219, 268 and 323.2 K for x = 0.01, 0.02, 0.04, respectively. The maximum magnetic entropy changes in a field change of 0~1.5 T are 6.1, 5.3 and 3.5J/kg·K for x = 0.01, 0.02 and 0.04, respectively.

Abstract: The concentration phase transition (CPT) in a two-dimensional ferromagnet was simulated by the Monte Carlo method. The description of the CPT was carried out using various order parameters (OP): magnetic, cluster, and percolation. For comparison with the problem of the geometric (percolation) phase transition, the thermal effect on the spin state was excluded, and thus, CPT was reduced to percolation transition. For each OP, the values ​​of the critical concentration and critical indices of the CPT are calculated.