Configurational Entropy Effects Research Articles

Multicomponent doping realized superior triple-conducting within cobalt-free Ruddlesden-Popper-type perovskite for Proton-conducting fuel cells cathode

Proton-conducting solid oxide fuel cells (H-SOFCs) are appealing for low-to-intermediate temperature operation due to their intrinsic lower activation energy and better ionic conductivity. Unfortunately, there are currently few acceptable and high-performing cathode materials available for H-SOFCs. Herein, we present a novel high performance multicomponent Ruddlesden-Popper (RP) type cathode Pr3Ni1.5Cu0.3Nb0.05Ta0.05Zr0.05Y0.05O7-δ (PNCNTZY) with superior triple conducting property. The multicomponent co-doping of Nb, Ta, Zr, and Y brings about the enhancement of configurational entropy and cocktail effect for improving H+/O2-/e- triple conductivity and oxygen vacancy concentration. Naturally, the ORR activity is improved by facilitated charge transfer and oxygen surface exchange, exhibiting reduced polarization resistance to just 0.24 Ω cm2 at 550 °C. When used as the cathode in H-SOFC single cells, excellent power production is demonstrated at 550 °C, with a peak power density of up to 0.84 W cm-2. Furthermore, the PNCNTZY sample shows adequate thermal compatibility with proton conductor electrolytes BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and then appropriate endurance durability (0.8 A cm-2 at 550 °C for about 250 h) due to their match of thermal expansion coefficient (TEC) brought about by the Co-free and partial replacement of larger-size elements. This extremely promising Co-free RP perovskite cathode for H-SOFCs produced by this work might provide a new type candidate and novel strategy for the commercialization of H-SOFCs.

Improved thermal properties and CMAS corrosion resistance of rare-earth monosilicates by adjusting the configuration entropy with RE-doping

The novel rare earth monosilicates (xRE1/x)2SiO5 (RE=Yb, Tm, Er, Y, Dy and Tb, x = 2–6) were prepared in order to establish the relationship between configurational entropy and lattice distortion, and the effect of configurational entropy on their properties was investigated. The results showed that the lattice distortion of (xRE1/x)2SiO5 increased gradually with the increase of configurational entropy, but the multi-principal component solid solution tended to form a highly symmetrical crystal structure when the configurational entropy was large enough, thus inhibiting the lattice distortion. (5RE1/5)2SiO5 had a maximum lattice distortion, which leaded to a relatively low thermal conductivity and coefficient of thermal expansion, and good CMAS corrosion resistance.

Single-stage reaction hot pressing route for dense refractory high entropy TiZrHfVNbTaB12-C ceramic composite

Hot pressing reaction-assisted sintering of novel refractory ceramic composite TiZrHfVNbTaB12-C was undertaken. The sintered material belongs to the class of Ultra-High-Temperature Ceramics (UHTCs). The sintering was done by utilizing transitional metal carbides and B4C at 1950 °С and 30 MPa for 8 min in a graphite die within an argon atmosphere. The ceramic demonstrated 98% density as measured by Archimedes’ method with accounted ceramic contamination by ZrO2 during initial carbide milling. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) revealed a single multimetal boride phase with AlB2-type (hexagonal, P6/mmm) structure and carbon inclusions. It is thought that the high concentrations of transitional metals lead to high configurational entropy effects and this produces a single boride phase. On those grounds, the ceramic belongs to the class of High Entropy Ceramics (HECs). The composite Vickers’ hardness HV was 12 ± 1 GPa and indentation toughness K1C was 4.3 ± 0.3 MPa·m1/2.

Metallurgical enhancement and mechanical performance of GTAW of AA5083 plates using medium and high-entropy fillers

The contemporary investigation focusses on the development of a welding technique to join AA5083 alloy plates using equimolar medium entropy alloy (4E-MEA - Fe0.25Al0.25Ni0.25Cu0.25) and high entropy alloy (5E-HEA - Fe0.2Al0.2Ni0.2Cu0.2Ti0.2) filler wires. A man-made combined cable wire method, was chosen to prepare the filler wires and the gas tungsten arc welding was used to conjoin the AA5083 plates. This study evaluated the metallurgical characteristics and mechanical performance of welded joints using 4E-MEA and 5E-HEA filler weldments and compared them with the standard ER5356 filler weldment. XRD analysis showed that both 4E-MEA and 5E-HEA weldments had evolved BCC and FCC phases, whereas microstructural analysis revealed a fine grain distribution without intermetallic phases. SEM analysis of the weldments revealed a heterogeneous microstructure (equiaxed and columnar grains) owing to the influence of the constituent elements. Solid solution formation, structural refinement, and high configurational entropy effects promoted grain refinement in the weldments as evidenced by EBSD analyses. The microhardness of 4E-MEA and 5E-HEA weldments increased by 18.3% and19.89%, respectively, compared with the standard filler weldment, while the tensile strength of 4E-MEA and 5E-HEA weldments increased by 24.3% and 27.9%, respectively and also obtained work-hardening rates were higher. It was observed that the heterogeneous microstructure in the weldment led to complicated plastic deformation and improved the mechanical responses. The presence of Fe and Ni increased ductility and inhibited the formation of intermetallic. The fractography results showed that the 4E-MEA and 5E-HEA filler weldments exhibited a combination of ductile and brittle fractures. Overall, the researchers demonstrated that the developed equimolar 4E-MEA and 5E-HEA filler wires could produce weldments with improved mechanical properties and can be utilized in automobile and shipbuilding applications.

The effect of configurational entropy on acoustic emission of P2-type layered oxide cathodes for sodium-ion batteries

Sodium-ion batteries (SIBs) see intensive research and commercialization efforts, aiming to establish them as an alternative to lithium-ion batteries. Among the reported cathode material families for SIBs, Na-deficient P2-type layered oxides are promising candidates, benefiting from fast sodium diffusion and therefore high charge/discharge rates. However, upon sodium extraction at high potentials, a transition from the P2 to O2 phase occurs, with the corresponding change in cell volume resulting in particle fracture and capacity degradation. A possible solution to this is to increase configurational entropy by introducing more elements into the transition-metal layer (so-called high-entropy concept), leading to some kind of structural stabilization. In this work, the acoustic emission (AE) of a series of P2-type layered oxide cathodes with increasing configurational entropy [Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2] is recorded during SIB operation and correlated to the materials properties, namely change in c lattice parameter and cracking behavior. A structure-property relationship between entropy, manifested in the extent of phase transition, and detected AE is derived, supported by the classification of signals by peak frequency. This classification in combination with microscopy imaging allows to distinguish between inter- and intragranular fracture. Relatively more intergranular and less intragranular crack formation is observed with increasing configurational entropy.

Accurate prediction of the solid-state region of the Ni-Al phase diagram including configurational and vibrational entropy and magnetic effects

The solid-state region of the Ni-Al phase diagram is predicted from first-principles calculations and Monte Carlo simulations through the cluster expansion formalism. In addition to the formation enthalpy and to the configurational entropy, the vibrational entropy and the magnetic enthalpy are included to calculate the Gibbs free energy of each phase. The computed phase diagram is in excellent agreement with the experimentally accepted phase diagram and provides information about the phase boundary between AlNi3 and Ni below 300 K. These results demonstrate the potential of this methodology to determine accurately the phase diagram of alloys of technological interest. Finally, the contributions of vibrational entropy and magnetic effects to the overall stability and solubility of the different phases are analyzed independently.

Comparison on structural andmagnetic properties of FeCoNi medium entropy alloy, FeCoNiAl and FeCoNiAlTi high entropy alloys

In the present study, we investigated the effect of configurational entropy on the phase evolution and magnetic properties of medium and high-entropy alloys. Three different, FeCoNi medium entropy alloys (MEA), FeCoNiAl, and FeCoNiAlTi high entropy alloys (HEAs) were synthesized through the mechanical alloying technique (MA). XRD analysis revealed the formation of the single fcc phase structure for FeCoNi MEA. The mixture of bcc and fcc phase is formed forFeCoNiAl HEA. However, for FeCoNiAlTi HEA the mixture of fcc, and bcc phases, along with a minor fraction of intermetallic R-phase is confirmed through the fitting of XRD data. The magnetic properties of FeCoNi MEA changed drastically by adding Al and Al, Tiwith Fe, Co, Ni as alloying elements for the formation of HEAs. The values of saturation magnetization (Ms) and coercivity (Hc) for FeCoNi MEA are 133.7 emu/g and 26.1 Oe, respectively. For FeCoNiAl HEA, the value of Ms decreased to 85.4 emu/g, and Hc increased to 74.2 Oe. However, for FeCoNiAlTiHEA, the value of Ms is reduced to 52.50 emu/g, and Hc increased to 90.55Oe. The present study clearly shows that the addition of different alloying elements significantly impacts the phase formation and the magnetic behavior of the MEA and HEAs.

Configurational Entropy-Enabled Thermostability of Cell Membranes in Extremophiles: From Molecular Mechanism to Bioinspired Design.

Understanding physicochemical interactions and mechanisms related to the cell membranes of lives under extreme conditions is of essential importance but remains scarcely explored. Here, using a combination of computer simulations and experiments, we demonstrate that the structural integrity and controllable permeability of cell membranes at high temperatures are predominantly directed by configurational entropy emerging from distorted intermolecular organization of bipolar tethered lipids peculiar to the extremophiles. Detailed simulations across multiple scales─from an all-atom exploration of molecular mechanism to a mesoscale examination of its universal nature─suggest that this configurational entropy effect can be generalized to diverse systems, such as block copolymers. This offers biomimetic inspiration for designing heat-tolerant materials based on entropy, as validated by our experiments of synthetic polymers. The findings provide new insight into the basic nature of the mechanism underlying the adaptation of organisms to extreme conditions and might open paths for designed materials inspired by entropic effects in biological systems.

Configurational Entropy Effect on Thermal and Mechanical Properties of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32 High‐Entropy Alloys

The configurational entropy effect on thermal and mechanical properties of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32 face‐centered cubic high‐entropy alloys is investigated by the molecular dynamics simulation with the second‐nearest‐neighbor modified embedded‐atom‐method potential. Using the heating process, 3000 and 2375 K are melting temperatures (Tm) of Pt1Pd1Rh1Co1 and Pt41Pd18Rh5Co32. Local structures around Co atoms become more distorted above 2425 K (about 0.81Tm) for Pt1Pd1Rh1Co1 and 1325 K (about 0.56Tm) for Pt41Pd18Rh5Co32. The Arrhenius equation shows that diffusion barriers of all element types in Pt1Pd1Rh1Co1 are about 50–89% higher than those in Pt41Pd18Rh5Co32, and the pre‐exponential factors of Pt1Pd1Rh1Co1 are about one order higher than those of Pt41Pd18Rh5Co32. Using the uniaxial compression simulation, the ultimate and yielding stresses of Pt1Pd1Rh1Co1 are about 88.3% and 53.4% higher than the corresponding values of Pt41Pd18Rh5Co32. For Young's modulus, Pt1Pd1Rh1Co1 is about 34.8% higher than that of Pt41Pd18Rh5Co32. At the yielding strain, the dislocation extraction algorithm results show that no local defected structures appear within Pt1Pd1Rh1Co1, whereas several nanoclusters of defected structures distribute randomly within Pt41Pd18Rh5Co32. At ultimate strain, multiple Shockley partial dislocations nucleate from the free surfaces for Pt1Pd1Rh1Co1, and more nanoclusters of defected structures appear within Pt41Pd18Rh5Co32, where Shockley partial dislocations nucleate.

Tensile behavior of hexagonal rare-earth-based low, medium, and high entropy alloys: Strengthening effect of configurational entropy

In the equiatomic hexagonal close packed high entropy alloy Ho-Dy-Y-Gd-Tb, there is a discrepancy, called the Gibbs paradox, between the extraordinary similarity of the constituent rare earth elements and its calculated configurational entropy. Equiatomic alloys made from one to five rare earth elements, with varying configurational entropy, are investigated for this work to evaluate this paradox in the context of tensile behavior. Assuming comparable microstructures and minimized solid solution strengthening due to the similarity of the constituent elements, a possible strengthening effect of the high configurational entropy is assessed. The alloys are successfully prepared via arc melting with comparable grain sizes and near equiatomic compositions. X-Ray diffraction, and elemental mappings with energy-dispersive X-Ray spectroscopy indicate single-phase microstructures in all alloys except for Ho–Y and Ho-Y-Gd. Tensile tests at room temperature show that the tensile strength of the single-phase alloys lies in the range of the pure elements, which confirms the hypothesis of minimized solid solution strengthening. Those alloys containing additional phases as well as the high entropy alloy show pronounced brittle behavior. No direct correlation between tensile behavior at room temperature and configurational entropy is observed. We state that this alloy system is a suitable candidate for evaluating the Gibbs paradox and disproving an entropy effect on the tensile behavior of this alloy system. This work contributes to understanding mechanical properties and the influence of configurational entropy on the hexagonal close packed high entropy alloy Ho-Dy-Y-Gd-Tb.

Effect of configurational entropy on phase formation, structure, and magnetic properties of deeply substituted strontium hexaferrites

Solid solutions based on SrFe 12 O 19 strontium hexaferrite with deep (up to at.67%) co-substitution of triply charged Fe 3+ iron cations by triply charged diamagnetic Al 3+ aluminum, Ga 3+ gallium, and In 3+ indium cations, as well as by paramagnetic Co 3+ cobalt and Cr 3+ chromium cations, were obtained by conventional ceramic technology. This type of substitution leads to the formation of high-entropy phases. The phase composition of the obtained samples was studied by powder X-ray diffraction. The configurational mixing entropy was calculated for all the obtained samples, and its influence on the processes of phase formation was studied. The unit cell parameters are calculated and their dependences on the 〈r B 〉 average ionic radius of the iron sub-lattice are plotted. The average grain size varied within 2–5 μm. The field and temperature properties of the magnetization of the obtained samples were studied. The M s saturation magnetization is determined using the Law of Approach to Saturation. The M r residual magnetization, SQR loop squareness and H c coercivity are also determined. Based on the obtained data, the k magnetic crystallographic anisotropy coefficient and the H a anisotropy field are calculated. All the obtained and calculated values are plotted depending on the 〈r B 〉 average ionic radius of the iron sub-lattice. All plotted dependencies are non-linear. The T mo magnetic ordering and T f freezing temperatures are obtained from the ZFC and FC magnetization data. The cluster nature of the magnetic behavior for all the samples is revealed. The average cluster diameter reaches ∼ 400 nm. The interpretation of the magnetic properties is made taking into account the effect of high configurational mixing entropy and magnetic dilution of the iron sub-lattice.

Facile low-energy and open-air synthesis of mixed-cation perovskite quantum dots for high-performance solar cells

Cesium-formamidinium (FA) lead triiodide (Cs1−xFAxPbI3) perovskite quantum dots (PQDs) are promising building blocks for photovoltaics. However, the mixed-cation colloidal PQDs are difficult to be synthesized in one pot because of the differences in optimal reaction temperatures of Cs (180 °C) and FA (80 °C) precursors; therefore, they are obtained by cation-exchange reactions between pre-synthesized CsPbI3 and FAPbI3 PQDs. Herein, one-pot synthesis of Cs1−xFAxPbI3 PQDs is developed at 60 °C in open air, dramatically reducing the process time and energy consumption compared to the conventional cation-exchange method. Computational calculations considering temperature effects reveal that the formation of mixed-cation PQDs is thermodynamically favorable even at the low synthesis temperature. The temperature effects dominate the mixing energy over the configurational entropy effect as the temperature increased, and thus Cs crystallizes more easily than FA at the synthesis temperature. This one-pot synthesis also allows fine-tuning of the A-site cations of Cs1−xFAxPbI3 PQDs, enabling the control of crystal structures and optical properties, thus optimizing photovoltaic performance. As a result, the fabricated Cs1−xFAxPbI3 PQD solar cells exhibit power conversion efficiencies (PCEs) up to 11.58 %, which is the highest among the reported solar cells fabricated using QDs synthesized at ≤ 60 °C in open air. The optimized solar cell retains 92 % of its initial PCE value after 1,083 h in dry air (dark and relative humidity < 10 %).

First principles prediction of the Al-Li phase diagram including configurational and vibrational entropic contributions

The whole Al-Li phase diagram is predicted from first principles calculations and statistical mechanics including the effect of configurational and vibrational entropy. The formation enthalpy of different configurations at different temperatures was accurately predicted by means of cluster expansions that were fitted from first principles calculations. The vibrational entropic contribution of each configuration was determined from the bond length vs. bond stiffness relationships for each type of bond and the Gibbs free energy of the different phases was obtained as a function of temperature from Monte Carlo simulations. The predicted phase diagram was in excellent agreement with the currently accepted experimental one in terms of the stable (AlLi, Al2Li3, AlLi2, Al4Li9) and metastable (Al3Li) phases, of the phase boundaries between them and of the maximum stability temperature of line compounds. In addition, it provided accurate information about the gap between Al3Li and AlLi solvus lines. Finally, the influence of the vibrational entropy on the correct prediction of the phase diagram is discussed. Overall, the methodology shows that accurate phase diagrams of alloys of technological interest can be predicted from first principles calculations.

P2-type layered high-entropy oxides as sodium-ion cathode materials

P2-type layered oxides with the general Na-deficient composition Na x TMO2 (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na+ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2 with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.

Effect of configurational entropy on dielectric properties of high-entropy perovskite oxides (Ce0.5,K0.5)x[(Bi0.5,Na0.5)0.25Ba0.25Sr0.25Ca0.25]1−xTiO3

Effect of configurational entropy on dielectric properties of high-entropy perovskite oxides (Ce0.5,K0.5)x[(Bi0.5,Na0.5)0.25Ba0.25Sr0.25Ca0.25]1−xTiO3

Configurational Entropy Effects on Glass Transition in Metallic Glasses.

Configurational entropy (Sconf) is known to be a key thermodynamic factor governing a glass transition process. However, this significance remains speculative because Sconf is not directly measurable. In this work, we demonstrate the role of Sconf theoretically and experimentally by a comparative study of a Zr-Ti-Cu-Ni-Be high-entropy metallic glass (HE-MG) with one of its conventional MG counterparts. It is revealed that the higher Sconf leads to a glass that is energetically more stable and structurally more ordered. This is manifested by ab initio molecular dynamics simulations, showing that ∼60% fewer atoms are agitated above Tg, and experimental results of smaller heat capacity jump, inconspicuous stiffness loss, insignificant structural change during glass transition, and a more depressed boson peak in the HE-MG than its counterpart. We accordingly propose a model to explain that a higher Sconf promotes a faster degeneracy-dependent kinetics for exploration of the potential energy landscape upon glass transition.

Phase, mechanical property and corrosion resistance evaluation of W-Nb-Ta-Ti and W-Nb-Ta-Ti-N medium entropy alloy thin films

Multicomponent alloy thin films including high entropy alloy (HEA) and medium entropy alloy (MEA) thin films have drawn lots of attention from researchers and industries because of their outstanding properties, such as high hardness, good wear and corrosion resistance. Among several kinds of multicomponent alloy systems, the refractory HEA and MEA are characterized by their high temperature strength and stable thermal properties. In this work, the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films were fabricated by a magnetron co-sputtering system. The structure of W-Nb-Ta-Ti-N coatings changed from BCC to B1 FCC nitride phase when the nitrogen concentration reached 42.6 at.%. The microstructure of BCC structured W-Nb-Ta-Ti-N thin films changed from a coarse columnar to a dense feature as the nitrogen content increased from 0 to 16.2 at.%. A maximum hardness of 24.4 GPa was obtained for the BCC structured W34.3Nb21.7Ta26.4Ti1.4N16.2 thin film. The best adhesion property and the lowest coefficient of friction were found for the FCC W31.1Nb9.6Ta13.1Ti3.6N42.6 nitride thin film. The corrosion resistance of 304SS substrate in 5 wt% NaCl aqueous solution was greatly enhanced by the deposition of the W-Nb-Ta-Ti and W-Nb-Ta-Ti-N refractory MEA thin films. The best corrosion resistance can be seen for the nitrogen-free W37.9Nb25.8Ta28.8Ti7.5 thin film due to its dense microstructure, highest Ta and Nb contents, high configurational entropy and sluggish diffusion effects.

The Role of Charge Density Coupled DNA Bending in Transcription Factor Sequence Binding Specificity: A Generic Mechanism for Indirect Readout.

The accurate reading of genetic information during transcription is essential for the expression of genes. Sequence binding specificity very often is attributed to short-range, usually specific interactions between amino acid residues and individual nucleotide bases through hydrogen bonding or hydrophobic contacts: "base readout" (direct readout). In contrast, many proteins recognize DNA sequences in an alternative fashion via "shape readout" (indirect readout), where many elements of the DNA sequence cooperate to localize the transcription factor. In this study, we use a coarse-grained protein-DNA model to investigate the origin of the sequence specificity of the protein PU.1 binding to its binding sites for a series of DNA sequences. We find that the binding specificity of PU.1 is achieved primarily via a nonspecific electrostatically driven DNA mechanism involving the change in the elastic properties of the DNA. To understand the underlying mechanism, we analyze how the mechanical properties of DNA change in relation to the location of the PU.1 bound along DNA. The simulations first show that electrostatic interactions between PU.1 and DNA can cause complex DNA conformational/dynamics changes. Using a semiflexible polymer theory, we find that PU.1 influences the DNA dynamics through a second-order mechanical effect. When PU.1 binds nonspecifically to the DNA via electrostatics, the DNA becomes stiffer and the protein slides along DNA in a search mode. In contrast, once the protein finds its specific binding site, the DNA becomes softer there. PU.1 thus locks into place through configurational entropy effects, which we suggest is a generic mechanism for indirect readout.

Configurational Entropy Effect on Thermal and Mechanical Properties of Pt1pd1rh1co1 and Pt41pd18rh5co32 High Entropy Alloys

Configurational Entropy Effect on Thermal and Mechanical Properties of Pt1pd1rh1co1 and Pt41pd18rh5co32 High Entropy Alloys

Synthesis of biocompatible high-entropy alloy TiNbZrTaHf by high-pressure torsion

High-entropy alloys (HEAs), a novel type of materials with high configurational entropy, have aroused a huge interest due to a promising range of functional properties including biocompatibility. In this study, the high-pressure torsion (HPT) method was implemented as a mechanical alloying route to synthesize biocompatible nanostructured HEAs with the bcc structure. An equiatomic quinary TiNbZrTaHf HEA was successfully synthesized via the HPT method and its characteristics were compared with the binary TiNb, ternary TiNbZr and quaternary TiNbZrTa alloys to have an insight into the effect of configurational entropy on microstructure and mechanical properties of these biomaterials. The grain size decreased, the strain-rate sensitivity reduced, and the hardness increased with increasing the number of principal elements from 2 to 3, but these variations became less significant with further increase in the configurational entropy. Small nanograins, solid solution hardening, dislocation activity together with high entropy effect in the HEA led to a high hardness of 564 Hv and a moderate elastic modulus of 79 GPa which are promising mechanical properties for biomedical applications.