Configurational Entropy Effects Research Articles

The potential of supramolecular synthon to develop coamorphous systems with tailored physical stability: Mechanistic insights integrating kinetics and thermodynamics

Coamorphous drug delivery systems have received increasing interest owing to their potential to improve the solubility, dissolution and bioavailability of poorly water-soluble drugs. However, the crystallization risk is one of major limitations in their application. It has been widely recognized that the coformer plays a vital role in physical stability of coamorphous formulation. Unfortunately, the screen of optimal coformer still adopts a trial-and-error method, which is time-consuming and expensive. Herein, a supramolecular synthon approach based on the interaction between functional groups, was exploited to design coamorphous systems (CMs) consisting of lurasidone hydrochloride (LH) and three coformers, saccharin (SAC), L-tryptophan (TRP), and L-cysteine hydrochloride (CYS). X-ray powder diffraction suggested the order of physical stability of the coamorphous systems was ranked as LH-CYS CM > LH-TRP CM > LH-SAC CM. The charge-assisted hydrogen bond between LH and coformer was confirmed by infrared spectroscopy and solid-state 13C NMR. Moreover, structural, electronic, and molecular interaction information, especially hydrogen bonding interactions, were quantified by theoretical calculations, including miscibility calculations, molecular dynamics simulations and quantum chemical calculations. It was revealed that LH-CYS CM exhibited the best miscibility, strongest binding energy and strongest H-bond with partially covalent character, demonstrating the significant role of supramolecular synthon in stabilizing coamorphous formulations. Interestingly, LH-TRP CM, not LH-CYS CM, exhibited the lowest molecular mobility among three coamorphous systems, which was inconsistent with their physical stability. But from thermodynamic perspective, the order of configurational entropy and physical stability of coamorphous systems was completely consistent. We shed light on the comprehensive effects of molecular mobility and configurational entropy on physical stability of coamorphous systems. Importantly, the relationship between supramolecular synthon and kinetic/thermodynamic mechanisms was also discussed, and the positive correlation between configurational entropy and intermolecular interactions was proposed in this paper. Our findings demonstrated the great potential of supramolecular synthon in designing coamorphous systems with tailored physical stability, and further provided a deeper insight into the mechanisms of physical stability of coamorphous systems.

Resolving the Role of Configurational Entropy in the Optimization of Mechanical, Thermal, and Microwave Dielectric Properties of SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 Ceramics.

The demand for high-performance microwave dielectric ceramics has surged with the proliferation of fifth-generation (5G) communication networks. In this work, SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 (x = 0-0.20) ceramics were designed by leveraging the unique properties of SrLaAlO4 ceramics and high-entropy engineering. The effects of configurational entropy (Sconf = 1.23R - 1.54R) on the mechanical, thermal, and microwave dielectric properties of SrLa(Al0.50-xGaxZn0.125Mg0.125Ti0.25)O4 ceramics were investigated. X-ray diffractometer and transmission electron microscope analyses confirmed that each composition belonged to the tetragonal structure with a space group of I4/mmm. Significant improvements in Vickers hardness were observed with increasing Sconf, reaching 8.05 GPa at Sconf = 1.54R compared to 5.64 GPa in SrLaAlO4 ceramics. Additionally, the increasing entropy showed great potential in reducing the thermal expansion coefficient (CTE) from 12.32 to 11.49 ppm/°C. The optimal quality factor (Q × f) of 98,000 GHz was achieved at Sconf = 1.37R, attributed to the optimization of intrinsic lattice energy and infrared-damped modes. The temperature coefficient of resonant frequency (τf) was successfully modified toward zero due to entropy-driven CTE and structural modifications. Excellent microwave dielectric properties with εr = 22.5, Q × f = 98,000 GHz, and τf = -2.0 ppm/°C were obtained at Sconf = 1.37R. This work highlights the potential of entropy-engineering in developing high-performance microwave dielectric ceramics, offering a promising pathway for the advancement of 5G communication components.

The effect of configurational entropy and refractory elements on the oxidation behaviour of high entropy carbides containing up to eight refractory elements

High entropy carbides (HECs) have attracted increasing attention due to their promising oxidation resistance properties. The oxidation behaviour of (Zr,Nb,Ta,Hf,Cr)C (HEC5-Cr), (Ti,V,Cr,Zr,Nb,Hf,Ta,W)C (HEC8-Cr), and (Ti,V,Zr,Nb,Mo,Hf,Ta,W)C (HEC8-Mo) powders was compared and studied from room temperature to 1200 °C. It was found that the oxidation onset temperatures (OOT) for the HEC5-Cr, HEC8-Cr, and HEC8-Mo powders were 790 °C, 688 °C, and 617 °C respectively. The high entropy effect benefits the structural stability of carbides and thus improves their oxidation resistance. However, there is no direct correlation between the configurational entropy value and the OOT of the studied HECs. Compared to the configurational entropy value, the refractory elements in HECs and the thermal stability of the produced oxides have a more significant impact on the oxidation resistance of HECs. Most of the group IV, V, and VI metals except W, Mo, and V have main oxides suitable for high-temperature applications, making them attractive candidates for oxidation-resistant HECs.

Synergistic Performance of Thermoelectric and Mechanical in Nanotwinned High-Entropy Semiconductors AgMnGePbSbTe5.

Introducing nanotwins in thermoelectric materials represents a promising approach to achieving such a synergistic combination of thermoelectric properties and mechanical properties. By increasing configurational entropy, a sharply reduced stacking fault energy in a new nanotwinned high-entropy semiconductor AgMnGePbSbTe5 is reached. Dense coherent nanotwin boundaries in this system provide an efficient phonon scattering barrier, leading to a high figure of merit ZT of ≈2.46 at 750K and a high average ZT of ≈1.54 (300-823K) with the presence of Ag2Te nanoprecipitate in the sample. More importantly, owing to the dislocation pinning caused by coherent nanotwin boundaries and the chemical short-range disorder caused by the high configurational entropy effect, AgMnGePbSbTe5 also exhibits robust mechanical properties, with flexural strength of 82MPa and Vickers hardness of 210HV.

Microstructure and thermoelectric properties of non-equimolar high-entropy [Ca(1-x)/3Sr(1-x)/3Ba(1-x)/3Lax]TiO3 perovskite ceramics

Entropy engineering has emerged as an important means of optimizing the properties of SrTiO3-based thermoelectric materials. However, the relationship between configurational entropy and thermoelectric properties is currently unclear. In this work, non-equimolar high-entropy thermoelectric ceramics [Ca(1-x)/3Sr(1-x)/3Ba(1-x)/3Lax]TiO3 (0.10 ≤ x ≤ 0.40) were prepared by spark plasma sintering. And the effects of composition and configurational entropy on the microstructure and thermoelectric properties of the materials were investigated. It is revealed that high entropy effect profoundly modified the microstructure of the material. The grain size decreases with increasing configurational entropy, the interaction of multiple cations leads to lattice distortions, and the sintering and annealing process induces the creation of oxygen vacancies, which significantly affect thermoelectric properties. The highest ZT (0.20) was obtained at a lanthanum content of 0.19 (ΔSConf=11.483 J/mol/K). This work provides theoretical and experimental bases for optimizing the thermoelectric properties of the materials by using high entropy design.

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