A phase stability study system for VLF propagation over short distances
Engineering design of transponder system for phase measurement of very low frequency signals
Graf, E. R.↗
SEARCH · Engineering Papers
Results for “PHASE STABILITY”
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Design of a fiber-optic transmitter for microwave analog transmission with high phase stability
The principal considerations in the design of fiber-optic transmitters for highly phase-stable radio frequency and microwave analog transmission are discussed. Criteria for a fiber-optic transmitter design with improved amplitude and phase-noise performance are developed through consideration of factors affecting the phase noise, including low-frequency laser-bias supply noise, the magnitude and proximity of external reflections into the laser, and temperature excursions of the laser-transmitter package.
Logan, R. T., Jr.↗
Defect and phase stability of solid solutions of Mg{sub 2}X with an antifluorite structure: An ab initio study
First principles calculations are done for Mg{sub 2}X (X=Si, Ge or Sn) antifluorite compounds and their solid solutions in order to investigate their pseudo-binary phase diagram. The formation energies of the end-member compounds agree qualitatively with the experiments. For X=Si and Ge, there is a complete solubility, but we observe a miscibility gap in the pseudo-binary phase diagram Mg{sub 2}Si-Mg{sub 2}Sn. This agrees with the most recent experiments and phase diagram assessments. Calculated electronic properties of Mg{sub 2}Si{sub 1-x}Sn{sub x} alloys qualitatively agree with experiments and in particular the energy bandgap decreases when Si is substituted by Sn. Supercell calculations are also done in order to determine the most stable defects and the doping induced by these defects in the three end-member compounds. We find that the intrinsic n-doping in pure Mg{sub 2}Si can be attributed to the presence of magnesium atoms in interstitial positions. In Mg{sub 2}Ge and Mg{sub 2}Sn, since other defects are stable, they can be also of p-type. - Graphical abstract: Evidence of a miscibility gap from the plot of the formation energy vs x{sub Si} (silicon content) for the solid solutions Mg{sub 2}Si-Mg{sub 2}Sn. Highlights: Black-Right-Pointing-Pointer First-principles study of the stability of Mg{sub 2}Si-Mg{sub 2}X alloys (X=Ge or Sn) and their defects. Black-Right-Pointing-Pointer Mg{sub 2}Si-Mg{sub 2}Ge alloys form a complete series of solid solutions. Black-Right-Pointing-Pointer Miscibility gap is found in Mg{sub 2}Si-Mg{sub 2}Sn alloys. Black-Right-Pointing-Pointer Interstitial defects are more stable in Mg{sub 2}Si and induce n-doping.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Equilibrium high entropy alloy phase stability from experiments and thermodynamic modeling
Long-term stability of high entropy alloys (HEAs) is a critical consideration for the design and practical application of HEAs. It has long been assumed that many HEAs are a kinetically-stabilized metastable structure, and recent experiments have confirmed this hypothesis by observing HEA ecomposition after long-termequilibration. In the presentwork,we demonstrate the use of the CALculation of PHAse Diagrams (CALPHAD) approach to predict HEA stability and processing parameters, comparing experimental long-term annealing observations to CALPHAD phase diagrams from a commercially-available HEA database. As a result, we find good agreement between single- and multi-phase predictions and experiments.
36 MATERIALS SCIENCE↗
Magnetic structure and phase stability of the van der Waals bonded ferromagnet Fe 3-x GeTe 2
The magnetic structure and phase diagram of the layered ferromagnetic compound Fe 3 GeTe 2 have been investigated by a combination of synthesis, x-ray and neutron diffraction, high-resolution microscopy, and magnetization measurements. Single crystals were synthesized by self-flux reactions, and single-crystal neutron diffraction finds ferromagnetic order with moments of 1.11(5)μ B /Fe aligned along the c axis at 4 K. These flux-grown crystals have a lower Curie temperature T c ≈ 150 K than crystals previously grown by vapor transport (T c = 220 K). The difference is a reduced Fe content in the flux-grown crystals, as illustrated by the behavior observed in a series of polycrystalline samples. As Fe content decreases, so do the Curie temperature, magnetic anisotropy, and net magnetization. Furthermore, Hall-effect and thermoelectric measurements on flux-grown crystals suggest that multiple carrier types contribute to electrical transport in Fe 3–x GeTe 2 and structurally similar Ni 3–x GeTe 2 .
36 MATERIALS SCIENCE↗
Phase stability of γ'-Ni 2 Cr and α-Cr in the Ni-Cr binary
For this study, the stability of the γ'-Ni 2 Cr long-range order (LRO) phase present on the Ni-Cr binary phase diagram was examined in a Ni-55Cr (wt. %) alloy. It is shown that the γ'-Ni 2 Cr phase is metastable, and that the two-phase γ-Ni + α-Cr phase field extends to room temperature. The as-cast alloy consisted of a typical dendritic microstructure, with Cr-rich primary α-Cr dendrites and a Cr-lean, γ-Ni interdendritic. Annealing the as-cast alloy at 500°C for 1000 h (γ'-Ni 2 Cr + α-Cr phase field) resulted in pockets of α-Cr and γ-Ni + γ'-Ni 2 Cr at the dendritic/interdendritic interface, with little change to the interdendritic γ-Ni microstructure. Annealing at 900°C for 4 h (γ-Ni + α-Cr phase field) resulted in the interdendritic precipitation of α-Cr, both as a continuous and discontinuous precipitate. Annealing at 900°C for 4 h followed by 500°C for 1000 h resulted in the interdendritic precipitation of α-Cr at 900°C, but no precipitation of γ'-Ni 2 Cr during subsequent annealing at 500°C. This behavior suggests that the γ'-Ni 2 Cr phase is not the equilibrium phase, but rather a metastable transition phase. Furthermore, it is speculated that this phase in more complex alloys (i.e. Alloy 690) is also metastable, and its metastability should be considered in applications involving long-term, high temperature exposures.
36 MATERIALS SCIENCE↗
Predicting the Phase Stability of Multicomponent High-Entropy Compounds
A generic method to estimate the relative feasibility of formation of high-entropy compounds in a single phase, directly from first principles, is developed. As a first step, the relative formation abilities of 56 multicomponent, AO, oxides were evaluated. These were constructed from five cation combinations chosen from A = {Ca, Co, Cu, Fe, Mg, Mn, Ni, Zn}. Candidates for multicomponent oxides are predicted from descriptors related to the enthalpy and configurational entropy obtained from the mixing enthalpies of two-component oxides. The utility of this approach is evaluated by comparing the predicted combinations with the experimentally realized entropy-stabilized oxide, (MgCoCuNiZn)O. In the second step, Monte Carlo simulations are utilized to investigate the phase composition and local ionic segregation as a function of temperature. This approach allows for the evaluation of potential secondary phases, thereby making realistic predictions of novel multicomponent compounds that can be synthesized.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
New Constraints on the Melting Temperature and Phase Stability of Shocked Iron up to 270 GPa Probed by Ultrafast X-Ray Absorption Spectroscopy
Studying the properties and phase diagram of iron at high-pressure and high-temperature conditions has relevant implications for Earth’s inner structure and dynamics and the temperature of the inner core boundary (ICB) at 330 GPa. Also, a hexagonal-closed packed to body-centered cubic (bcc) phase transition has been predicted by many theoretical works but observed only in a few experiments. The recent coupling of high-power laser with advanced x-ray sources from synchrotrons allows for novel approaches to address these issues. Here, we present a study on shock compressed iron up to 270 GPa and 5800 K probed by single-pulse (100 ps FWHM) x-ray absorption spectroscopy (XAS). Based on the analysis of the XAS spectra, we provide structural identification and bulk temperature measurements along the Hugoniot up to the melting. These results rule out the predicted transition to a high-temperature bcc phase and allow one to discriminate among existing equations of state models and melting curves. In particular, we report the first bulk temperature measurement in shock compressed iron on the melting plateau at 240(20) GPa and 5345(600) K. The melting curve resulting from our work extrapolates to a temperature of 6202(514) K at 330 GPa and represents a refined upper bound for the ICB temperature. Published by the American Physical Society 2024
Balugani, S.↗
FPGA-Based Optical Cavity Phase Stabilization for Coherent Pulse Stacking
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an field-programmable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5kHz, and stabilized at an individually-prescribed round-trip phase with 0.7deg and 2.1deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.
43 PARTICLE ACCELERATORS↗
First-Principles Study of Phase Stability of bcc XZn (X = Cu, Ag, and Au) Alloys
First-principles density-functional theory is used to study the phase stability/instability and anomalies in the formation of the high-temperature bcc phases of X Zn (X = Cu, Ag, and Au) alloys. Although from perhaps a naive point of view, their properties are expected to monotonically depend on the noble-metal (X) column position in the periodic table, this is not the case. For example, the middle-column AgZn alloy has a lower bcc order-disorder (critical) temperature than the CuZn and AuZn alloys above and below in the column. It is shown that this and other nonmonotonic behaviors can be explained in terms of a competition between atomic-size effects and X-atom d-orbital spatial extent. For example, charge-density studies and pair-potential modeling of X Zn alloys show that the effective Ag-Zn bond is significantly weaker than either the Cu-Zn or Au-Zn bond at their respective equilibrium lattice constants. Furthermore, we find that an increased atomic-core size effect initially weakens the X-Zn bonding as one goes from CuZn to AgZn, but then the larger d-orbital spatial extent for higher principal quantum numbers becomes a more dominant effect and increases the bonding from AgZn to AuZn. In conclusion, this study is focused on the highly symmetric cubic high-temperature phases, where relative bond-strength magnitudes should be far more important than any bond-directionality effects; the lattice parameters, bulk moduli, elastic constants, Debye temperatures, heats of formation, and order-disorder temperatures for the bcc phases of the three X Zn alloys are calculated and compared with experiment.
36 MATERIALS SCIENCE↗
Ab-initio predictions of phase stability, electronic structure, and optical properties of (0001)-MAX surfaces in M 2 AC (M = Cr, Zr, Hf; A = Al, Ga)
In this work, we report MAX phases' surface properties, which are essential for thin-film technology due to their excellent resistance to high-temperature oxidation, corrosion, and wear. The surface stability, electronic, and optical properties of 0001-surfaces in M 2 AC (M = Zr, Hf, Cr; A = Al, Ga) are investigated and compared with their bulk counterparts. The interplay between chemical bonding and charge distribution is discussed from electronic structure, including the Fermi surfaces. Four possible (0001)-terminated surfaces are considered by breaking M - C and M-A bonds in which cleavage energy of M - C is higher than M-A. The Cr–Al bond in Cr 2 AlC is stronger than other M-A bonds. The charge density of valance A-p electrons redistributes in the surface area, distinct from that of the bulk. The A- and M(C)-terminated (0001)-surfaces are the most stable and energetically favorable terminations due to lower surface energies. The optical properties of the most stable (0001)-surfaces were also investigated to understand the dielectric and photoconductive behavior in the (0001)-terminated surfaces of M 2 AC.
36 MATERIALS SCIENCE↗
Phase stability in the two-dimensional anisotropic boson Hubbard Hamiltonian
The two dimensional square lattice hard-core boson Hubbard model with near neighbor interactions has a ‘checkerboard’ charge density wave insulating phase at half-filling and sufficiently large intersite repulsion. When doped, rather than forming a supersolid phase in which long range charge density wave correlations coexist with a condensation of superfluid defects, the system instead phase separates. However, it is known that there are other lattice geometries and interaction patterns for which such coexistence takes place. In this paper we explore the possibility that anisotropic hopping or anisotropic near neighbor repulsion might similarly stabilize the square lattice supersolid. Lastly, by considering the charge density wave structure factor and superfluid density for different ratios of interaction strength and hybridization in the ˆx and ˆy directions, we conclude that phase separation still occurs.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Phase stability, swelling, microstructure and strength of Ti 3 SiC 2 -TiC ceramics after low dose neutron irradiation
In this study, M n+1 AX n (MAX) phase Ti 3 SiC 2 materials were neutron irradiated at ~400, ~630, and 700 °C to a fluence of ~2 × 10 25 n/m 2 (E > 0.1 MeV). After irradiation at ~400 °C, anisotropic c-axis dilation of ~1.5% was observed. Room temperature strength was reduced from 445 ± 29 MPa to 315 ± 33 MPa and the fracture surfaces showed flat facets and transgranular cracks instead of typical kink-band deformation and bridging ligaments. XRD phase analysis indicated an increase of 10–15 wt% TiC. After irradiation at ~700 °C there were no lattice parameter changes, ~5 wt% decomposition to TiC occurred, and strength was 391 ± 71 MPa and 378 ± 31 MPa. The fracture surfaces indicated kink-band based deformation but with lesser extent of delamination than as-received samples. Finally, Ti 3 SiC 2 appears to be radiation tolerant at ~400 °C, and increasingly radiation resistant at ~630–700 °C, but a higher temperature may be necessary for full recovery.
36 MATERIALS SCIENCE↗
Coupled Chemical and Mechanical Control of Phase Stability in Lanthanide-Substituted BiVO 4
Doping is widely used to enhance the photoelectrochemical performance of BiVO 4 , yet solubility limits and polymorphic stability constrain compositional tuning. Here, in this study, the role of trivalent cation substitution (Ln = La, Nd, Dy, Ho, Y) on pressure-induced phase transformations in Bi 1–x Ln x VO 4 (x ≤ 0.5) is described. Powder X-ray and neutron diffraction reveal that increasing Ln content stabilizes the tetragonal zircon-type polymorph under ambient conditions, while applied pressures of up to ∼5 GPa promote conversion to the monoclinic fergusonite-type polymorph. In-situ neutron diffraction on Bi 0.8 La 0.2 VO 4 shows a reversible monoclinic to tetragonal transition near 2–3 GPa with a bulk modulus of 147 GPa. The extent of conversion depends strongly on dopant identity, concentration, and synthetic route, with mixed-phase solid-state samples converting more efficiently than phase-pure coprecipitated materials. These results demonstrate pressure as a viable pathway to access metastable, doped BiVO 4 compositions beyond conventional solubility limits.
Sypkes, Kathryn I. [University of Sydney, NSW (Aus↗
Tuning phase stability and short-range order through Al doping in ( CoCrFeMn ) 100 - x A l x high-entropy alloys
For ( CoCrFeMn ) 100 - x A l x high-entropy alloys, we report on the phase evolution with increasing Al content ( 0 ≤ x ≤ 20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of ( CoCrFeMn ) 100 - x A l x alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the chemical ordering behavior of arbitrary complex solid-solution alloys—an ideal approach for predictive design of high-entropy alloys. The predictions confirm our present experimental findings and other reported ones.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Growth of crystalline Al{sub 2}O{sub 3} via thermal atomic layer deposition: Nanomaterial phase stabilization
We report the growth of crystalline Al{sub 2}O{sub 3} thin films deposited by thermal Atomic Layer Deposition (ALD) at 200 °C, which up to now has always resulted in the amorphous phase. The 5 nm thick films were deposited on Ga{sub 2}O{sub 3}, ZnO, and Si nanowire substrates 100 nm or less in diameter. The crystalline nature of the Al{sub 2}O{sub 3} thin film coating was confirmed using Transmission Electron Microscopy (TEM), including high-resolution TEM lattice imaging, selected area diffraction, and energy filtered TEM. Al{sub 2}O{sub 3} coatings on nanowires with diameters of 10 nm or less formed a fully crystalline phase, while those with diameters in the 20–25 nm range resulted in a partially crystalline coating, and those with diameters in excess of 50 nm were fully amorphous. We suggest that the amorphous Al{sub 2}O{sub 3} phase becomes metastable with respect to a crystalline alumina polymorph, due to the nanometer size scale of the film/substrate combination. Since ALD Al{sub 2}O{sub 3} films are widely used as protective barriers, dielectric layers, as well as potential coatings in energy materials, these findings may have important implications.
36 MATERIALS SCIENCE↗
Phase Stability in Nanocrystals: A Predictive Diagram for Yttria–Zirconia
Predicting the polymorphic stability of nanocrystals entails taking into account the thermodynamic effects from solid–vapor interfaces. With recent advances in microcalorimetry, it is finally possible to obtain reliable surface energy data which allow building of predictive diagrams, such as the usual phase diagrams for bulk crystals, for nanocrystals. Yttria doped zirconia (YZ) is currently utilized in a variety of applications; making it one of the most studied oxide systems to date. However, the polymorphism of nanocrystalline YZ (nYZ) is much less understood as compared to its bulk counterpart, and the stability conditions of cubic, tetragonal, monoclinic, and amorphous polymorphs at the nanoscale is so far only empirically defined. In this work, we present a new predictive nanoscale phase diagram for nYZ using unprecedented data on surface energies and bulk enthalpies acquired by microcalorimetry. The phase diagram shows the stable zirconia polymorph as a function of the composition and size. This is a useful tool and an important and novel advancement to relatively untouched bulk phase diagrams, which holds the key for reliable materials' design.
Drazin, John W.↗
Influence of valence electron concentration on Laves phases: Structures and phase stability of pseudo-binary MgZn 2-x Pd x
A series of pseudo-binary compounds MgZn 2-x Pd x (0.15 ≤ x ≤ 1.0) were synthesized and structurally characterized to understand the role of valence electron concentration (vec) on the prototype Laves phase MgZn 2 with Pd-substitution. Three distinctive phase regions were observed with respect to Pd content, all exhibiting fundamental Laves phase structures: 0.1 ≤ x ≤ 0.3 (MgNi 2 -type, h P24; MgZn 1.80 Pd 0.20(2) ), 0.4 ≤ x ≤ 0.6 (MgCu 2 -type, cF 24; MgZn 1.59 Pd 0.41(2) ), and 0.62 ≤ x ≤ 0.8 (MgZn 2 -type, hP 12: MgZn 1.37 Pd 0.63(2) ). Refinements from single-crystal X-ray diffraction indicated nearly statistical distributions of Pd and Zn atoms among the majority atom sites in these structures. Interestingly, the MgZn 2 -type structure re-emerges in MgZn 2–x Pd x at x ≈ 0.7 with the refined composition MgZn 1.37(2) Pd 0.63 and a c/a ratio of 1.59 compared to 1.64 for binary MgZn 2 . Electronic structure calculations on a model “MgZn 1.25 Pd 0.75 ” yielded a density of states (DOS) curve showing enhancement of a pseudogap at the Fermi level as a result of electronic stabilization due to the Pd addition. Moreover, integrated crystal orbital Hamilton population values show significant increases of orbital interactions for (Zn,Pd)–(Zn,Pd) atom pairs within the majority atom substructure, i.e., within the Kagomé nets as well as between a Kagomé net and an apical site, from binary MgZn 2 to the ternary “MgZn 1.25 Pd 0.75 ”. Multi-centered bonding is evident from electron localization function plots for “MgZn 1.25 Pd 0.75 ”, an outcome which is in accordance with analysis of other Laves phases.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗