Phase Transition In Cu Research Articles

Dynamics of Cu–Zr metallic glass devitrification under ultrafast laser excitation revealed by atomistic modeling

The physics of metallic glass local devitrification employing ultrafast laser irradiation is the cradle of complex phenomena that are still not understood despite its applicative potential in material processing for nanotechnology. This paper reports a theoretical simulation combining the two temperature model and classical molecular dynamics simulations to unravel the mechanisms that lead to the localized phase transition in Cu–Zr metallic glass. According to observations, the initial composition of amorphous samples plays an essential role, in addition to nonequilibrium thermodynamic processes caused by the laser energy deposition that alters the atomic environment. We further demonstrate that specific compositions devitrify despite its high glass-forming ability. The thermodynamic conditions fostering the emergence of a stable nanocrystalline phase are clearly established. The compressive pressure wave and the rapid heating process caused by ultrafast laser energy deposition synergistically contribute to disrupt the microstructure of the glass significantly, thereby initiating the devitrification process. Results are discussed using additional classical MD simulations that provide valuable insights for interpreting the distinct contributions of temperature and pressure to the phase transformation. Finally, the impact of the formed nanocrystals on the phononic thermal conductivity of the alloy is presented confirming the potential application of the laser-induced devitrification process for the development of a new generation of nanoarchitectured materials.

Study of effects of corrosion temperature on corrosion resistance of Cu-C alloys to liquid Ga

The corrosion interface characteristics and corrosion behavior of Cu-C alloys in liquid Ga at 100–180 ℃ were studied in this paper. The corrosion mechanism of Cu-C alloys was microscopically studied via the first-principles calculation based on the density functional theory (DFT). The results, the diffusion of Ga atoms leads to the phase transition of Cu in the Cu-C alloy and the generation of the corrosion product CuGa2. The corrosion rate of the Cu-C alloy is related to the dissolution rate, and growth rate and exfoliation rate of corrosion product layer. C led to much better corrosion resistance of Cu-C alloys.

Evidence of structural and two magnetic phase transitions in Cu doped La2FeMnO6 double perovskites

In this report, we have addressed a comprehensive study on the structural phase transitions with the help of a combination of high temperature x-ray diffraction and temperature dependence Raman spectroscopy. We also report the magnetic ground state of all the samples at room temperature and 5 K. The combined high temperature x-ray diffraction and temperature dependence Raman study suggests that the samples undergo structural phase transitions from orthorhombic to tetragonal to cubic dominated mixed phase. With the help of x-ray photoelectron spectroscopy, we confirmed the presence of multi-oxidation states of Fe and Mn ions. The temperature evolution of magnetization data has been recorded at a field of 100 Oe and temperature range between 2 K and 300 K, and reveals the presence of two magnetic phase transitions for pristine, 10% and 20% doping of Cu in the composition La 2 FeMn 1−x Cu x O 6 . The magnetic study of all the samples reveal that the magnetic ground state of all the samples shows paramagnetic nature at room temperature, whereas at lower temperature all the samples are ferromagnetic except the highest doped sample which is purely paramagnetic. The law of approach to saturation method is imposed in the saturation region of M-H curve observed at 5 K. The transition temperature decreases with the amount of Cu doping, due to the substitution of Cu in Mn-site resulting in destroy of the Mn 3+ -O 2- - Mn 4+ bridges which is responsible for weakening of double exchange interaction between Mn 3+ and Mn 4+ . • Temperature dependent XRD has shown a structural phase transition from orthorhombic to tetragonal to cubic space group. • Temperature evolution of the phononic modes predominantly influenced by the lattice degrees of freedom. • Magnetic studies have shown two phase transitions confirming low temperature FM phase with different ordering mechanisms.

Phase Transformation in Quasi-Two-Dimensional Quantum Antiferromagnet Cu(tn)Cl2 (tn = 1,3-Diaminopropane)

Cu(tn)Cl2 belongs to family of molecular magnets with low-dimensional magnetism mediated by hydrogen bonds. Here, the X-ray diffraction, electron paramagnetic resonance, specific heat measurements, and ab initio calculations performed within the framework of density functional theory have been employed to investigate the structural phase transition in Cu(tn)Cl2. Satellite reflections in the X-ray diffraction pattern from single crystals, visible anomaly in the specific heat measured in a zero magnetic field, rapid growth of the EPR resonance line width, along with the increase of the g-factors in the vicinity of 160 K are indicative of the structural phase transition in Cu(tn)Cl2. Our results reveal that this system undergoes transition from a disordered structure of the Pnma symmetry to a modulated structure with the Pnma(0β0)s00 superspace group. The transition is reversible and driven by the reorientation of the diaminopropane ligands. The density functional theory studies support results of our specific heat measurements.

Phase Transitions of Cu and Fe at Multiscales in an Additively Manufactured Cu-Fe Alloy under High-Pressure.

A state of the art, custom-built direct-metal deposition (DMD)-based additive manufacturing (AM) system at the University of Michigan was used to manufacture 50Cu–50Fe alloy with tailored properties for use in high strain/deformation environments. Subsequently, we performed preliminary high-pressure compression experiments to investigate the structural stability and deformation of this material. Our work shows that the alpha (BCC) phase of Fe is stable up to ~16 GPa before reversibly transforming to HCP, which is at least a few GPa higher than pure bulk Fe material. Furthermore, we observed evidence of a transition of Cu nano-precipitates in Fe from the well-known FCC structure to a metastable BCC phase, which has only been predicted via density functional calculations. Finally, the metastable FCC Fe nano-precipitates within the Cu grains show a modulated nano-twinned structure induced by high-pressure deformation. The results from this work demonstrate the opportunity in AM application for tailored functional materials and extreme stress/deformation applications.

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

Summary Discovering novel materials and attaining higher performance are the eternal pursuit of thermoelectric materials research. Here, we report a material series, (Cu1−xAgx)2(Te1−ySy) (0.16 ≤ x ≤ 0.24, 0.16 ≤ y ≤ 0.24), which adopts a complex orthorhombic structure differing from any known crystal structure of (Cu/Ag)2(S/Te). This material series is featured by the crystal-amorphicity duality induced by the large anionic size mismatch: a crystalline sublattice of highly size-mismatched anions Te/S coexists with an amorphous-like sublattice of cations Cu/Ag. In the context of structure-property correlation, the crystal-amorphicity duality gave rise to not only interesting electrical properties but also exceptionally low lattice thermal conductivities from 300 to 1,000 K. A state-of-the-art figure of merit zT of 2.0 is obtained in the x = y = 0.22 sample at 1,000 K. These results give insights into crystal-amorphicity duality as a paradigm-shifting materials design approach to develop high-performance thermoelectric materials.

Solid phase transition of Cu precipitates in a low carbon TRIP assisted steel

The evolution behavior of Cu precipitates under intercritical tempering in a low carbon low alloy steel is presented in the study here. A complete crystal structure transformation process of Cu precipitate is presented together with newly discovered steps. The complete transformation sequence of crystal structure of Cu precipitates in the alloy system was (I) Cu-rich nano-order clusters→9R Cu→detwinned 9R Cu→transition phase (detwinned 9R + FCC)→FCC Cu and (II) Cu-rich nano-order cluster→non twin 9R Cu→FCC Cu. The entire evolution process of Cu precipitates was caused by the continuous enrichment of Cu atoms in Cu precipitates and the size of Cu precipitates. In the present study, we have discovered the increase of Cu content in Cu-rich nano-ordered clusters, the movement rule of twin planes and the combination of twin variants in the multiple twin 9R Cu, the transition rule from 9R structure to FCC structure.

Thermal properties and segregation phenomena in transition metals and alloys: modeling based on modified cohesive-energies

In spite of free-atom electronic-relaxation contributions to transition-metal cohesive-energies, numerous studies have misused the latter instead of using the solid-state interatomic bond-energy in modeling bulk and surface properties. This work reveals that eliminating the free-atom contributions from experimental cohesive-energies leads to highly accurate linear correlations of the resultant bond-energies with melting temperatures and enthalpies, as well as with inverse thermal-expansion coefficients, specifically for the fcc transition-metals. Likewise, predictions of surface segregation phenomena in Cu–Pd and Au–Pd alloys on the basis of the modified energetics are in much better agreement with reported low-energy ion scattering spectroscopy (LEISS) experimental results, as compared to the use of cohesive-energy values. A last demonstration of the problem and its solution involves the significant impact of the modification on segregation (separation) phase transitions in Cu–Ni model nanoparticles.

Electric-field control of the ferro-paraelectric phase transition in Cu:KTN crystals

We report an efficient approach for ferro-paraelectric phase transition control in Cu:KTN crystals by using AC electric fields. Based on a dielectric loss mechanism, the thermal effect is induced directly inside the crystal without using extra thermal sources or complicated thermostat systems. By adjusting either the amplitude or the frequency of an AC electric field, we can easily and precisely control the ferro-paraelectric phase transition process which concurs with dynamic development of polar nanostructures of KTN crystals. In addition, we use a laser beam to probe in real time the dynamic process of crystalline phase transition. The study is important for developing novel electro-optic and ferroelectric devices for a wide range of photonic applications.

Surface phase transition in Cu–Fe solid solutions

Particles of a second phase on grain boundaries and free surface in copper-based solid solutions with iron were observed. Previously the samples were tested on diffusion creep for surface free energy measurements. The test method is based on measuring of time dependences of stress in foils. The stresses were low (up to 300kPa) and most of time the foils were balancing around zero stress. Experiments were performed in a dry hydrogen atmosphere. The temperature range was from about 900°C to 1070°C. The volume concentration of iron for second phase formation on surfaces was about 0.4at% Fe. The particles had uniform distribution on the grain boundaries and free surface. The average sizes are from 20nm at 0.4at% to about 1µm at 0.74at% Fe. The surface phase transition is confirmed by measurements of viscosity and surface energy. Surface free energy isotherm has extremum near 0.4at% Fe and temperature dependence of viscosity has a gap at Fe concentration higher 0.4at%.

Influence of annealing process on phase transition of Cu–Al nanoferrites synthesized by a coprecipitation method

As-synthesized CuAl0.8Fe1.2O4 nano-crystalline samples prepared by the co-precipitation method were annealed at different temperatures T. The nanoferrite samples were characterized using X-ray diffraction and FT-IR and Mössbauer spectroscopy. This study proved that the structural phase of the nanoparticles was transformed with T from cubic to tetragonal due to the tetragonal distortion of a Jahn–Teller effect (JTE) of Cu2+ ions. The transformation process was pronounced at 600°C and predominated at 1000°C. All spectra and parameters were affected by JTE. The crystallite size, strain, distortion parameter and inter-chain distance showed dependence on T, whereas the lattice parameters did not. Six absorption bands were observed in the IR spectra, where their position and intensity, threshold frequency and Debye temperature were T dependent. The Mössbauer spectra were affected by T. The hyperfine magnetic field of the A- and B-sites, magnetization and area ratio of B/A-sites were deduced and discussed as functions of T. The estimated cation distribution explained the motion of metallic ions between the crystal sublattices as T increases.

Martensitic phase transition in Cu–14%Al–4%Ni shape memory alloys studied by Brillouin light scattering

The paper presents the influence of the martensitic phase transition on hypersonic thermally excited surface acoustic waves propagating in Cu–14%Al–4%Ni (wt%) shape memory alloy. Non-destructive and non-contact testing using Brillouin light scattering spectroscopy permitted determination of the elastic constants of austenite versus temperature. Experimental results obtained for martensite were interpreted using the proposed model of the cubic to orthorhombic martensitic phase transition based on the Landau model of a first-order phase transition. Additionally we adopted the approximation of the domain structure of martensite by a polycrystalline sample using the Voigt–Reuss–Hill procedure of averaging the elastic constants.

Phase transformation of Cu precipitates from bcc to fcc in Fe–3Si–2Cu alloy

Phase transition of Cu precipitates during aging of an Fe–3Si–2Cu alloy was studied by transmission electron microscopy. The precipitation of 3–5-nm-sized body-centered cubic (bcc) Cu in ferrite matrix was confirmed by high-angle annular dark-field scanning transmission electron microscopy imaging. The bcc Cu precipitates transformed to 9R Cu as they grew. Many 9R Cu precipitates were twinned, but untwinned 9R Cu particles were also observed. The 9R Cu transformed to twinned face-centered cubic (fcc) Cu by the glide of ±a/3 [100]9R Shockley-type partial dislocations. Formation of the 3R structure previously reported could not be confirmed in this study. Finally, twins in fcc Cu precipitates disappeared to form stable fcc Cu particles. The importance of electron beam-orientation-dependent moiré fringes in the correct identification of Cu structure is discussed in detail.

Ferroelectric Phase Transition in Cu-doped BaTiO3 Crystals

The paper examines the ferroelectric-paraelectric phase transition in Cu:BaTiO3 single crystals. Using thermo-currents and dielectric measurements, we found for pure samples the phase transition temperature to be close to Curie temperature (Tc=120°C) with an anisotropy of the dielectric constantε.The lowering of temperature Tm, corresponding to the maximum of pyroelectric signal, with the increase of concentration of impurities is confirmed by measurements of ε. Moreover, the e(T) curves show progressive broadening as well as higher peak with the increase of impurity concentration, and the transition becomes more and more diffuse. The same effect occurs when the samples are subjected to a laser irradiation (λ=5145Ǻ). During annealing, crystals lose copper and Tm is thereafter observed to increase again. BaTiO3 is a displacive ferroelectric (having high permittivity k-values) which undergoes a first order phase transition. Ions substitutions have an effect on the lattice dynamics attributed to charge transfer to Ti and a lowering of elastic forces in BaTiO3. Kewwords: Ferroelectric transition; BaTiO3 single crystals; Thermo-currents; Dielectric constant. © 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. DOI: 10.3329/jsr.v1i2.1876

Jahn—Teller Phase Transition in Cu0.50TiO(PO4): Powder Structural Characterization of the β‐Variety and Thermal Study.

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Jahn–Teller phase transition in Cu 0.50TiO(PO 4): Powder structural characterization of the β-variety and thermal study

The thermal study of Cu 0.50TiO(PO 4), by X-ray diffraction and DSC, shows a phase transition α → β with a hysteresis (∼600 °C during heating; ∼300 °C during cooling). Single crystals have been obtained for the α-phase but the β-phase can only be stabilised at room temperature as a powder mixture with α. Structural characterization of the β-variety has been done with diffraction data (X-ray Cu Kα 1 and neutrons) using a powder rich in β-phase (α(20%) + β(80%)). A monoclinic cell ( a = 7.1134(7) Å; b = 7.7282(7) Å; c = 7.3028(7) Å; β=119.30(1)°; V = 350.1(1) Å 3) has been found for β-phase, space group P2 1/ c. An “ ab initio” structure determination has been done, and the Rietveld refinement leads to cR wp = 0.150 and R B = 0.041. The results from the X-ray data were confirmed by refinements from neutron data. Similarly to the α-phase, the structure of β-Cu 0.50TiO(PO 4) can be described as a TiOPO 4 framework constituted of chains of tilted corner-sharing [TiO 6] octahedra running parallel to the c axis and cross linked by [PO 4] tetrahedra. Ti atoms are displaced from the centres of the octahedral units, leading to long (2.27 Å) and short (1.73 Å) Ti–O(1) bonds. The [CuO 6] octahedra exhibit a typical Jahn–Teller distorted coordination with four short equatorial Cu–O bonds (2 × 1.93 Å and 2 × 2.06 Å), and two longer apical Cu–O bonds (2 × 2.33 Å). The two longer Cu–O bonds are almost parallel to the b axis. The transition from the α to the β-phase is characterized by a “rocking” of the Jahn–Teller elongation from the ( a, c) plane to the b direction accompanied by a relatively strong expansion of the cell volume.

In situ X-ray study of order–disorder phase transitions in Cu–Al–Be melt spun ribbons

The disorder–order phase transitions in Cu–Al–Be shape memory alloys were studied by in-situ X-ray diffraction. Isothermal measurements in an inert gas chamber were made on ribbons of Cu–Al–Be alloys, obtained by melt spinning. A position sensitive detector was used for a fast record of the X-ray signal on a θ–θ geometry diffractometer. Each ribbon was used as the heating element, avoiding the need of a heating sample holder and obtaining a better measurement of the temperature with a thermocouple attached directly to the ribbon. The order transition was followed at different temperatures after a high temperature annealing (700 °C) in the disordered β-phase region. A first order transition was observed from disordered β (A2) to ordered β1 (DO3), without prior β (B2) ordering. No precipitation was detected during this fast measuring procedure.

Investigation of Ultrasonic and Acoustoelectric Properties of Ferroelectric-Semiconductor Crystals

The ultrasonic velocity and attenuation anomalies were observed near phase transitions (PT) in CuInP2(S,Se)6 semiconductor crystals, where S was partially substituted by Se. It was shown that, crystals became piezoelectric not only in low temperatures below PT in ferroelectric phase but also at room temperature, which is far above the phase transition and under DC bias electric field, the electrostriction induced piezoelectricity appears. The anomalies of ultrasonic velocity, attenuation, second harmonic, and acoustoelectric voltage were also observed near the phase transitions in Cu 6 PS 5 I single crystals. These crystals belong to the polar symmetry group 3m at room temperature and exhibit a ferroelastic phase transition at 270 K.

Solubility diagram of the Cu–Ni nanosystem

The application of equilibrium thermodynamics to a nanosystem changes Gibbs’s rule ofgeometrical thermodynamics. This fact leads to the necessity to reconsider the phasediagram and solubility curve concepts. The notions of ‘solubility diagram’, ‘solidus’,‘liquidus’ are used to discuss the case of phase transition in Cu–Ni nanoparticles. It isshown that, in the limit where thermodynamic arguments remain valid, the solubilitydiagrams of nanoparticles are functions of their size and nucleation mode. This isdemonstrated for different sizes.

A Molecular Dynamics Investigation into the Cooling Characteristics of Ni and Cu Alloys at High Pressure

This paper studies the phase transitions of Cu and Ni alloys as they cool from melting temperature to room temperature under high-pressure conditions. The interatomic forces acting between the atoms are modeled by the tight-binding potential. Control over the environmental pressure and the cooling temperature is maintained by a canonical ensemble (N, P, T) system. The numerical results confirm that the metal phase transition is influenced significantly by the pressure conditions, even in the case of pure Cu and Ni metals. Three specific transition pathways are identified for the Cu and Ni alloys as they cool from melting temperature to room temperature, namely a transition at the melting temperature to a crystalline structure, a transition at the glass transition temperature to a glass (amorphous) structure, and finally solidification at the melting temperature followed by a subsequent transition at the glass transition temperature. The results reveal that glass transition generally occurs at lower pressures in alloys with higher Cu compositions, while glass transition following prior solidification tends to takes place at higher pressures in alloys with higher Ni compositions.