Ideal Phase Research Articles

Dual Additive‐Assisted Layer‐by‐Layer Processing for 19.59% Efficiency Quasi‐Bulk Heterojunction Organic Solar Cells

AbstractThe ideal vertical phase separation active layer morphology is crucial for the photoelectric conversion of organic solar cells. In this work, a layer‐by‐layer sequential deposition method is used to prepare D18/L8‐BO‐based organic solar cells and a dual additives strategy is adopted to construct the ideal active layer. Additive DIM regulates the crystallization of the D18 layer, and additive DIO induces L8‐BO to diffuse into the interior of the D18 layer to form a vertical composition distribution with large donor/acceptor interpenetrated regions. The improvement of active layer induced by DIM and DIO dual additives promote exciton generation and dissociation, shorten charge transfer distance, and improve carrier dynamics. With improved charge transport performance and suppressed carrier recombination, the short‐circuit current density and fill factor of the D18/L8‐BO quasi‐bulk heterojunction organic solar cells are improved simultaneously, and the power conversion efficiency is boosted significantly from 18.21% to 19.59%. Moreover, the improved photovoltaic performance is further verified in D18/Y6 and PM6/L8‐BO‐based organic solar cells, which implies the generalizability of the dual additive‐assisted layer‐by‐layer ‐sequential deposition method.

Enhanced wear resistance of in-situ nanoscale TiC reinforced Ti composites fabricated by additive manufacturing

The poor wear resistance of Ti alloys limits its application in the orthopedic and dental surgery field. TiC as an ideal reinforcement phase can improve wear resistance due to its high hardness, low coefficient of friction, and good bio-compatibility. However, the wettability of the interface between the TiC and Ti matrix is poor, which leads to low mechanical properties and wear resistance. In situ TiC formed through the addition of a C source can enhance interfacial bonding. In this work, the Ti-graphite composites are prepared by Laser powder bed fusion (LPBF). On the one hand, the LPBF can prepare various complex porous shapes according to the personalized customized demand. On the other hand, the LPBF can provide a high cooling rate, suppressing grain growth and refining grains, and also can obtain equally distributed nanoscale TiC particles. The results show that the composites are mainly composed of Ti, TiC, and residual graphite. With the increase of graphite content, the amount of TiC increases and the grain becomes smaller, and the microhardness increases from 317 HV0.2 to 408 HV0.2. Meanwhile, the Ti-1.5 wt%Gr composite has a low friction coefficient, volume of wear, and wear rate, which is attributed to the high hardness of TiC particles and lubrication of graphite. The oxide on the surface of the wear mark is mainly composed of TiO2 and TiO. The main wear mechanisms of the composites are oxidation wear and adhesive wear.

Strain-induced continuous transition from orthorhombic to hexagonal-like phase in Ti-36Zr-6Nb alloy with abnormally high strain hardening

The deformation mechanism of the α″-type Ti-36Zr-6Nb alloy exhibiting an abnormal strain hardening behavior was investigated using in-situ high-energy X-ray diffraction and ex-situ transmission electron microscopy under tensile tests. It was discovered that the orthorhombic α″ phase distorts successively toward hexagonal symmetry during tension through coupled atomic shear and shuffle, and the successive distortion of the α″ lattice contributes to the abnormally high strain hardening of the Ti-36Zr-6Nb alloy. Notably, the orthorhombic α″ phase does not transform into an ideal hexagonal phase during tension but instead transforms into a hexagonal-like phase. The hexagonal-like phase exhibits shear and shuffle components that are very close to those of the ideal hexagonal phase. Additionally, the strain-induced α″ to hexagonal-like martensitic transition was found to be partially reversible during unloading. The present study offers an in-depth understanding of the abnormal strain hardening behavior and the strain-induced phase transition behavior of the α″-type titanium alloys.

Concentration Scales and Solvation Thermodynamics: Some Theoretical and Experimental Observations Regarding Spontaneity and the Partition Ratio.

The solvation thermodynamics (ST) formalism proposed by A. Ben-Naim is a mathematically rigorous and physically grounded theory for describing properties related to solvation. It considers the solvation process as the transfer of a molecule ("solute") from a fixed position in the ideal gas phase to a fixed position within the solution. Thus, it removes any contribution to the solvation process that is not related to the interactions between this molecule and its environment in the solution. Because ST is based on statistical thermodynamics, the natural variable is number density, which leads to the amount (or "molar") concentration scale. However, this choice of concentration scale is not unique in classical thermodynamics and the solvation properties can be different for commonly used concentration scales. We proposed and performed experiments with diethylamine in a water/hexadecane heterogeneous mixture to confront the predictions of the ST, based on the amount (or "molar") concentration scale, and the Fowler-Guggenheim formalism, based on the mole fraction scale. By means of simple acid-base titration and 1H NMR measurements, it was established that the predictions of differences in the solvation Gibbs energy and the partition ratio (or "partition coefficient") of diethylamine between water and hexadecane are consistent with the ST formalism. Additionally, with current literature data, we have shown additional experimental support for the ST. However, due to the arbitrariness of the relative amount of solvents in the partition ratio, the choice of a single concentration scale within the classical thermodynamics is still not possible.

What do we learn from impurities and disorder in high-Tc cuprates?

A series of experimental studies established that the differing morphologies of the phase diagrams versus hole doping nh of the various cuprate families are mostly controlled by defects and disorder. In the minimally disordered cuprate Yttrium Baryum Copper Oxide (YBCO) we introduced controlled detfects that allowed us to probe the metallic and superconducting states. We demonstrate that the extent of the spin glass phase and the superconducting dome can be controlled by the concentration of spinless (Zn, Li) impurities substituted on the planar Cu sites. NMR frequency shift measurements establish that these defects induce, in their vicinity, a cloud with a Kondo-like paramagnetic behavior. Its “Kondo” temperature and spatial extent differ markedly between the pseudogap and strange metal regimes. We have performed transport measurements on single crystals with a controlled content of in-plane vacancies introduced by electron irradiation. At high T, the inelastic scattering of the carriers has been found independent of disorder and completely governed by the excitations of the correlated electronic state. The low T upturns in the resistivity associated with single-site Kondo-like scattering are qualitatively in agreement with local magnetism induced by spinless impurities. The apparent metal insulator crossover is only detected for a very large defect content, and part of the large resistivity upturn remains connected with Kondo-like paramagnetism. In the superconducting state, the defect-induced reduction of Tc scales linearly with the increase in residual resistivity induced by disorder. High-field magnetoresistance experiments permit us to determine the paraconductivity due to superconducting fluctuations. The latter vanishes beyond a temperature T’c and a field H’c that both decrease with increasing in-plane defect content. In the pseudogap regime, the weaker decrease of T’c with respect to that of Tc reveals a large loss of superconducting phase coherence in the presence of disorder. In light of our experimental results, we initiate a discussion of its interplay with pair breaking. Our data also permit us to confirm that the differing phase diagrams are due to competing orders or disorders that are family-specific. In the ideal phase diagram of a disorder-free cuprate, 2D superconductivity should persist at low doping. This ensemble of experimental results provides serious challenges for the theoretical understanding of superconductivity in these correlated electron systems.

Phase-Induced Strain Effect to Synthesize an Iron-Doped Orthogonal Cobalt Selenide Electrocatalyst for the Oxygen Evolution Reaction.

The etching effect has the capability to control atom doping and trigger phase transformation, thereby enhancing the electrocatalytic reaction. Herein, iron-doped cobalt selenide (Fe-CoSe2) nanoparticle-decorated carbon nanofibers (Fe-CoSe2/CNFs) are synthesized by assembling an FeCo-Prussian blue analogue (FeCo-PBA) cube precursor with polyacrylonitrile fibers and then treating with hydrochloric acid, followed by gas phase selenization. The Fe-CoSe2/CNFs catalyst exhibits a large surface area and a porous structure, facilitating the permeation of electrolytes. Moreover, orthorhombic CoSe2 is obtained, which is in favor of improving the oxygen evolution reaction (OER). By modulating the etching time, the ideal crystal phase and the optimal amount of the dopant (Fe) can be achieved, thus showing favorable OER activity. Specifically, the Fe-CoSe2/CNFs electrocatalyst enables high electrocatalytic activity for the OER with a low overpotential of 263 mV to drive a current density of 10 mA cm-2 in 1 M KOH. A small Tafel slope of 51 mV dec-1 shows fast charge transfer kinetics. Density functional theory (DFT) calculations reveal that Fe-doped orthorhombic CoSe2(111) can modulate the electron structure, contributing to OH- adsorption ability. Given this, a strategy for phase transformation induced by etching technology is proposed to improve the intrinsic activity of the catalyst.

A van der Waals Model of Solvation Thermodynamics.

Exploiting the van der Waals model of liquids, it is possible to derive analytical formulas for the thermodynamic functions governing solvation, the transfer of a solute molecule from a fixed position in the ideal gas phase to a fixed position in the liquid phase. The solvation Gibbs free energy change consists of two contributions: (a) the high number density of all liquids and the repulsive interactions due to the basic fact that each molecule has its own body leading to the need to spend free energy to produce an appropriate cavity to contain the solute molecule; (b) the ubiquitous intermolecular attractive interactions lead to a gain in free energy for switching-on attractions between the solute molecule and neighboring liquid molecules. Also the solvation entropy change consists of two contributions: (a) there is an entropy loss in all liquids because the cavity presence limits the space accessible to liquid molecules during their continuous translations; (b) there is an entropy gain in all liquids, at room temperature, due to the liquid structural reorganization as a response to the perturbation represented by solute addition. The latter entropy contribution is balanced by a corresponding enthalpy term. The scenario that emerged from the van der Waals model is in qualitative agreement with experimental results.

Resource allocation for practical phase shift STAR-RIS enabled MISO-NOMA wireless network with non ideal hardware

This study investigates the sum secrecy rate SRsum of a simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS)-enabled multiple input single-output (MISO) non-orthogonal multiple access (NOMA) downlink network with non-ideal hardware defects (HWDs) at the transceivers. Earlier STAR-RIS studies assumed an ideal phase shift model, with each element reflect and transmit the signal without regard to its phase shift. The proposed practical phase shift model accounts for the phase-dependent amplitude variation in the reflection and transmission (RAT) coefficients. The goal is to maximize the SRsum through an alternating optimization (AO) iterative algorithm, leverages a classical semidefinite relaxation (SDR) for beamformer vector design (BVD), and employs an interior point method (IPM) to calculate NOMA power allocation factors αt,αr. The analysis focuses on the evaluation of the SRsum in scenarios with eavesdroppers, under the consideration of both ideal and practical phase shift cases. The study examines the impact of different non-ideal HWDs on the SRsum of the system and provides insights into vulnerabilities and limitations arising from these effects.

The effect of phase-shifting transformer angle value on system congestion and determination of ideal phase angle

The effect of phase-shifting transformer angle value on system congestion and determination of ideal phase angle

In Situ Local Imaging of Ferromagnetism and Superconductivity in RbEuFe4As4.

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics, but the study is limited by low superconducting (Tc) and magnetic (Tm) transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in situ diamagnetic and ferromagnetic responses of RbEuFe4As4 with high Tc and Tm. We observed significant suppression of the superfluid density in the vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3d conduction electrons. Intriguingly, we observed multiple ferromagnetic domains that should be absent in an ideal magnetic helical phase. The formation of these domains demonstrates a weak c-axis ferromagnetic component probably arising from the Eu spin-canting effect, indicative of possible superconductivity-driven domain Meissner and domain vortex-antivortex phases, as revealed in EuFe2(As0.79P0.21)2. Our observations highlight that RbEuFe4As4 is a unique system that includes multiple interplay channels between superconductivity and ferromagnetism.

High-order allpass cascade-connected phase-system design utilizing fractional polynomial errors

ABSTRACT This paper proposes a nonlinear optimization method for designing a high-order recursive allpass digital phase system that comprises several cascade-connected second-order (SO) allpass sections. This method first splits a given phase design specification (approximation target) into a set of equal sub-specifications, and then the equal sub-specification acts as the ideal phase for each of the SO sections. Since an SO section can be designed via employing a linear programming to minimize a linear fractional error function, this splitting process generates an excellent starting point (good initial values for the coefficients of the cascaded SO sections) for further minimizing the overall approximation error. This paper first derives a wide variety of fractional polynomial error functions for designing cascade-connected allpass phase systems of different high orders, and then shows that a high-order cascade-connected allpass phase system can be designed by utilizing a nonlinear solver to minimize the peak deviation of such a fractional polynomial error. Using the derived fractional polynomial error functions in the system design enables the system designer to find an excellent starting point for further minimizing the approximation error and thus reach a convergent design solution. This paper first derives a set of fractional polynomial errors, and then adopts the eighth-order cascade-connected phase system design to exemplify the effectiveness of the fractional-polynomial-error-based design tactic. Furthermore, the stability of the cascade-connected high-order allpass system can be readily checked via confirming that all of the cascaded SO sections have their poles inside the unit circle in the complex plane.

Cladding-free Fermi arc surface states and topological directional couplers in ideal photonic Weyl metamaterials

Photons can freely propagate in a vacuum, making it not a simple insulator but rather a conductor for photons. Consequently, in topological photonics, domain wall structures with opposing effective mass terms are used as cladding to confine electromagnetic waves. This approach is necessary to demonstrate topological edge/surface waves and Fermi arc surface states (FASS). Here, we show that the cladding-free FASS with high field localization at the boundary can be achieved using ideal Weyl gyromagnetic metamaterials (GMs). In these GMs, the ideal Weyl semimetal phase exists due to the dispersionless longitudinal modes. At the boundary of the GMs-vacuum system, the cladding-free FASS connects the projections of Weyl nodes with opposite chirality, thanks to the bulk-boundary correspondence principle. We further confirm that chiral boundary modes can propagate without experiencing scattering or backward reflection, i.e., they can advance seamlessly approximately various types of defects. Remarkably, various types of topological directional couplers are achieved by utilizing cladding-free FASS in an ideal gyromagnetic medium. Our theoretical analysis reveals that the underlying operational principle for accomplishing these nonreflecting directional couplers is due to the single coupling channel between the cladding-free FASS and the multi-type scatterers of the continuous media. Furthermore, the controllable propagation and topological directional coupling of cladding-free FASS can be further explored by adjusting the ideal gyromagnetic medium and boundary configurations of the continuous media system. This research offers increased flexibility for the development of cladding-free and directionally coupled topological devices.

Sum‐rate maximization for downlink multiuser MISO URLLC system aided by IRS with discrete phase shifters

AbstractIntelligent reflecting surface (IRS) has recently been considered as a potential technology for realizing ultra‐reliable and low‐latency (URLLC) in wireless networks. This paper proposes a resource optimization scheme to maximize the sum‐rate for an IRS‐assisted downlink multiuser multi‐input single‐output (MISO) URLLC system. For the perfect CSI scenario, we jointly optimize each user's block‐length and packet‐error probability, the precoding vectors at the base station (BS), and the passive beamforming with discrete phase shifts at the IRS. Given the problem's complexity, we design a computationally efficient iterative algorithm using successive convex approximation (SCA) and semidefinite relaxation (SDR) techniques to obtain a locally optimal solution. Specifically, for the imperfect CSI scenario, we construct a robust resource optimization problem model and incorporate the S‐procedure to address the impact of channel uncertainty, proposing an iterative algorithm based on the alternating optimization (AO) method to achieve a locally optimal solution. Simulation results demonstrate that: 1) An IRS equipped with a 2‐bit quantized resolution phase shifter is sufficient to achieve a system sum‐rate comparable to that of an ideal phase shifter; 2) Compared to other Baseline schemes, Algorithm 2 exhibits better robustness and superior performance gains under imperfect CSI.

Controlling vertical phase separation and crystallization via solvent synergy strategy to empower layer-by-layer processed organic solar cells

The novel sequential layer-by-layer (LbL) processed organic solar cells (OSCs) have attracted continuous attention due to their advantages of ideal vertical phase separation, efficient charge transport and collection, and potentiality for large-scale production from laboratory to factory. Herein, a solvent synergy strategy is put forward to control morphology, crystallization and vertical phase distribution of blend films, which means the donor PM6 and acceptor Y6 treated by high/low boiling point solvents are fabricated using LbL solution process, respectively. Based on device with a configuration of ITO/ZnO/PM6:Y6/MoO3/Ag, OSCs derived from the solvent synergy strategy can obtain a remarkable power conversion efficiency (PCE) up to 15.03%, which is comparable to that of the bulk heterojunction devices prepared by conventional one-step solution method. This impressive result provides an insightful understanding of phase segregation and crystalllization in LbL processed OSCs assisted by the solvent synergy strategy. It lays the foundation for fabrication and optimization of high-performance, large-area OSCs in industrial production.

Tailoring Cyano Substitutions on Quinoxaline‐based Small‐Molecule Acceptors Enabling Enhanced Molecular Packing for High‐Performance Organic Solar Cells

AbstractCyanation is a common chemical modification strategy to fine‐tune the energy levels and molecular packing of organic semiconductors, especially materials used in organic solar cells (OSCs). Generally, cyanation is used to modify the end groups of high‐performance small‐molecule acceptors (SMAs). However, the cyanation strategy has not been investigated on the central backbone of SMAs, which could introduce stronger intermolecular interaction and enhance the π–π stacking for rapid charge transport. This paper, for the first time, reports a new cyanation strategy on the central benzo‐quinoxaline core and synthesizes two novel A‐DA'D‐A type SMAs, named BQx‐CN and BQx‐2CN, with mono‐ and di‐cyanide groups, respectively. Through tailoring the number of CN groups, the BQx‐CN‐based OSC exhibits the best device performance of 18.8%, which is significantly higher than the non‐cyano BQx‐based one. The reason for the superior performance of BQx‐CN‐based devices can be attributed to the fine‐tuned energy level, stronger packing, and ideal phase segregation, which lead to superior exciton dissociation, faster charge transport, and suppressed recombination, therefore the highest fill factor (FF) and power conversion efficiencies (PCE). The research demonstrates the effectiveness of the cyanation strategy on the central core of SMAs for enhanced molecular packing and better performance of OSCs.

Green Surfactant Assisted-Solidified Floating Organic Drop Micro-Extraction (SA-SFODME) for the Preconcentration of Trace Lead with Determination by Flame Atomic Absorption Spectrometry (FAAS)

Determination of trace lead from environmental samples was carried out by solidified floating organic drop microextraction for preconcentration before analysis by flame atomic absorption spectrometry. The determination of lead from environmental samples, even at trace levels, was possible with an ordinary flame atomic absorption spectrometer (FAAS). The lead formed a hydrophobic complex with the anionic surfactant sodium dodecyl benzene sulfonate (SDBS), and this hydrophobic complex was extracted into the 1-dodecanol drop. Parameters affecting analytical performance have been studied. The optimum pH value was 3.5. The optimum sample volume, SDBS concentration, and extraction solvent volume were 75 mL, 50 mM in dodecanol, and 75 µL, respectively. The optimum extraction time was determined as 30 min, the optimum extraction temperature was 45 °C, the optimum mixing speed was 650 rpm and the ideal extraction phase volume was 0.50 mL. Methanol has been shown to be effective when used as a diluent. Using the optimum conditions, the enhancement factor was 106, and the limit of detection (3s) and precision were 3.3 ng/mL and 2.3% (n = 9,15 ng/mL), respectively. The limit of quantification (LOQ) (10s) was 10 ng/mL and the linear working range was 15-100 ng/mL. The accuracy was evaluated by certified reference material analysis. The optimized method was applied to the determination of Pb(II) from environmental water samples. This method follows the principles of green analytical chemistry.

Monolayer directional metasurface for all-optical image classifier doublet.

Diffractive deep neural networks, known for their passivity, high scalability, and high efficiency, offer great potential in holographic imaging, target recognition, and object classification. However, previous endeavors have been hampered by spatial size and alignment. To address these issues, this study introduces a monolayer directional metasurface, aimed at reducing spatial constraints and mitigating alignment issues. Utilizing this methodology, we use MNIST datasets to train diffractive deep neural networks and realize digital classification, revealing that the metasurface can achieve excellent digital image classification results, and the classification accuracy of ideal phase mask plates and metasurface for phase-only modulation can reach 84.73% and 84.85%, respectively. Despite a certain loss of degrees of freedom compared to multi-layer phase mask plates, the single-layer metasurface is easier to fabricate and align, thereby improving spatial utilization efficiency.

Selective leaching behavior of Nd from spent NdFeB magnets treated with combination of selective oxidation and roasting processes

Selective leaching behavior of the spent NdFeB magnets was investigated to find out how controlled phase system through the roasting conditions gave an impact on the performance of the selective leaching. The pre-formed Nd2O3 by the selective oxidation made it possible to prevent the formation of NdFeO3 at high roasting temperature. This resulted in the ideal Nd2O3 and Fe2O3 phase system, which was obtained by roasting at 660 °C, suitable for the selective leaching of Nd. While the roasting at 600 °C was still not enough to get full oxidation, the roasting at 720 °C made the NdFeO3 formed. These characteristics with the roasting conditions affected leaching behavior. The NdFeB powder sample of 32 μm particle diameter, roasted at 600 °C showed the highest Nd leaching efficiency as well as the highest Fe leaching efficiency, which seemed to be ascribed to the existence of the metallic Fe. The poor leaching efficiency for the large powder size after roasting was ascribed to the poor diffusion characteristic of the H2SO4 solution. With the controlled phase system, the 100% leaching efficiency of Nd could be obtained by reducing the particle size to 16 μm. The formation of NdFeO3 as a co-product, which had resistance to the reaction with the leaching agent, could prevent the dissolution of Nd2O3 around the NdFeO3 layer. Thus, the 720 °C roasting condition showed the lowest leaching efficiency. The co-product Fe2O3 also showed good resistance to leaching so its leaching efficiency was just 5–6% after the leaching time of 3–4 h.

First-principles calculation of phase transitions and mechanical properties of (CoCrNi)100−xAlx (0 ≤ x ≤ 28 at. %) high-entropy alloys

In the two-phase high-entropy alloys (HEAs) (i.e., FCC, BCC), the modulation of the BCC phase is crucial for improving the mechanical properties of FCC-type HEAs. The stability of the phase of (CoCrNi)100−xAlx (0 ≤ x ≤ 28 at. %) HEAs is studied using first-principles calculations. The Al content on the phase transition of CoCrNi HEAs is discussed. The theoretical values of lattice parameter a (x) increase with increasing Al concentration, which is consistent with the earlier experimental findings. The crystal structure transitions from the FCC to BCC crystal structure as the Al content increases. At x < 11.8 at. %, Al alloying lowers the elastic stability of the BCC and FCC phases, whereas excessive Al doping causes the FCC phase to BCC phase transition (x > 21.4 at. %). The crystal structure has an ideal mix phase of BCC and FCC at x = 18.8 at. %, which results in excellent strength-ductility synergy of HEAs. There is a phase transition point at x = 11.8 at. %, where there may be a competition between phase transition and dislocation nucleation, which improves strength. The work in this paper provides new ideas for the design of future high-performance duplex phase HEAs.

The optimal algorithm for eliminating nonlinear error in phase measurement profilometry based on global statistical phase feature function

In a digital fringe projection structured light system, the nonlinear phase error is generated by the gamma effect of both the projector, camera, and other electronic devices. One of the existing nonlinear correction methods is active correction by projecting ideal fringes as far as possible, and the other is passive compensation after capturing aberrant fringes. The former has higher accuracy but needs to capture a large number of fringe patterns, while the latter does not need many fringe patterns, but is not only greatly affected by random noise and out-of-focus effects, but also has poor accuracy. In this paper, an optimal algorithm for eliminating nonlinear error based on global statistical phase feature function (GSPF) is proposed. The phase distribution can be estimated from the difference between the global cumulative distribution function (CDF) and the normalized (CDF). For an ideal fringe pattern without nonlinear error and a fringe pattern with nonlinear error, the region wrapped by the x-axis normalized CDF is much smaller than the region wrapped by the x-axis global CDF, and the larger the nonlinear error is, the larger the difference between the two is. Therefore, the GSPF can be used for nonlinear error correction. Then the optimal nonlinear error correction is performed based on the minimum difference between the compensated phase entropy and the ideal phase entropy. The method does not require too many steps of phase-shifting, and only three fringe patterns are needed to realize accurate and robust correction. Experimental results show that the method is fast, highly accurate and robust. Using this technique, high accuracy measurements can be achieved with the traditional three-step phase-shifting algorithm.