Impact of the A-site rare-earth ions (Ln3+ – Sm3+, Eu3+, Gd3+) on structure and electrical properties of the high entropy LnCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3 perovskites

High entropy perovskites LnCr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2O₃ ceramics were produced by solid-state reactions from oxides. The B-site chemical composition was fixed (Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2) and A-site composition was varied by the rare-earth ions (Ln = Sm³⁺, Eu³⁺ and Gd³⁺). The entropy of B-sublattice mixing was 1.609R J/(mol*K). The dependences of the lattice parameters, microstructure features, and electrical properties were discussed as function of the A-site rare-earth ions. The correlation of the lattice parameters with the nature of the A-site rare earth ions was demonstrated. Impact of the rare-earth ions in A-site on microstructural parameters was observed. Charge conduction mechanisms were discussed in details for a wide range of temperatures.     

Effect of niobium doping on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries

Key issues including poor rate capability and limited cycle life span should be addressed for the extended application of LiNi_0.5Co_0.2Mn_0.3O₂ cathode. The suppressed Li⁺/Ni²⁺ site exchange, enlarged LiO₂ inter-slab space and reduced impedance, which could facilitate the structure stability, were achieved by controlled Niobium (Nb) doping and contributed to enhanced performance even at elevated temperature (55 °C). The detailed role of the doped Nb was investigated thoroughly and systematically with the help of XRD, SEM, XPS and related electrochemical tests. The full and accurate results demonstrate that the Li(Ni_0.5Co_0.2Mn_0.3)_0.99Nb_0.01O₂ sample with appropriate Nb doping amount possess high capacity retention of 93.77% after 100 cycles at 1.0 C and improved rate performance with 125.5 mA h g⁻¹ at 5.0 C, which are much better than that of the LiNi_0.5Co_0.2Mn_0.3O₂. Moreover, at high temperature of 55 °C, Nb doping shows more remarkable effect on stabilizing the structure and 88.63% of the initial reversible capacity could be retained, which is ~20% higher than the LiNi_0.5Co_0.2Mn_0.3O₂. This study intensively determines that controlled Nb doping could be effectively maintain the structure stability of advanced LiNi_0.5Co_0.2Mn_0.3O₂ cathode and promote the development of high energy density lithium ion batteries.     

The characteristics of Li(Ni1/3Co1/3Mn1/3)O2 particles prepared from precursor particles with spherical shape obtained by spray pyrolysis

Spherical and fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles were prepared using spray pyrolysis. Precursor particles with mixed Mn₂O₃, Co₃O₄ and NiO compositions were prepared using spray pyrolysis from aqueous and polymeric precursor solutions. The precursor particles prepared from the aqueous solution had hollow and porous morphologies. The precursor particles prepared from the polymeric precursor solution with citric acid and ethylene glycol were spherical in shape and had filled morphologies. The spherical precursor particles with filled morphologies formed spherical, fine-sized Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles with filled morphologies after post-treatment with LiOH. The mean crystallite sizes of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared from spray solutions with and without lithium at the post-treatment temperature of 800 °C were 56 and 31 nm, respectively. The initial discharge capacities of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles prepared using spray pyrolysis from spray solutions with and without lithium were 178 and 181 mAh g⁻¹, respectively, after a post-treatment temperature of 800 °C.     

Microstructure and electrical conductivity of La0.9Sr0.1 Ga0.8Mg0.2O2.85-Ce0.8Gd0.2O1.9 composite electrolytes for SOFCs

(100-x) wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - x wt.% Ce_0.8Gd_0.2O_1.9 (x = 0, 5, 10, 20) electrolytes were prepared by solid-state reaction. The composition, microstructure, and electrical conductivity of the samples were investigated. At 300 ~ 600°C, the pure La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 electrolyte has a higher conductivity compared to the composite electrolytes, but at 650 ~ 800°C the 95 wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - 5 wt.% Ce_0.8Gd_0.2O_1.9 composite electrolyte presents the highest conductivity, reaching 0.035 S cm⁻¹ at 800°C. The cell performances based on La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85-Ce_0.8Gd_0.2O_1.9 electrolytes were measured using Sr₂CoMoO₆-La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 as anode and Sr₂Co_0.9Mn_0.1NbO₆ -La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 as cathode, respectively. At 800°C, the measured open-circuit voltages are higher than 1.08 V, and the maximum power density and current density of the fuel cell prepared with 95 wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - 5 wt.% Ce_0.8Gd_0.2O_1.9 electrolyte reach 192 mW cm⁻² and 720 mA cm⁻², respectively.     

Synthesis and characterization of Mo-doped LiNi0.5Co0.2Mn0.3O2 cathode materials prepared by a hydrothermal process

The lithiated metal oxide precursor with α-NaFeO₂ structure and low crystallinity prepared by a hydrothermal process is verified to be Li-Ni-Co-Mn-Mo composite oxide. The layered Li(Ni_0.5Co_0.2Mn_0.3)_1-xMo_xO₂ (x=0, 0.005, 0.01 and 0.02) cathode material with high crystallinity for lithium ion batteries (LIBs) is obtained from the lithiated metal oxide precursor by heat treatment. The results of SEM and EDS mapping characterization indicate that the molybdenum is distributed in the materials homogeneously. The effects of molybdenum on the structure, morphology and electrochemical performances of the LiNi_0.5Co_0.2Mn_0.3O₂ are extensively studied. According to the results of electrochemical characterizations, the Li(Ni_0.5Co_0.2Mn_0.3)_0.99Mo_0.01O₂ sample exhibits the best discharge cycling performance with capacity retention of 97.0% after 50 cycles, and an excellent rate performance of 125.5 mAh·g⁻¹ at 8C rate. The Li(Ni_0.5Co_0.2Mn_0.3)_0.99Mo_0.01O₂ sample also shows a lower potential polarization, smaller impedance parameters and a larger Li⁺ diffusion by CV and EIS analyses.     

Rapid microwave-assisted synthesis and magnetic properties of high-entropy spinel (Cr0.2Mn0.2Fe0.2Co0.2-xNi0.2Znx)3O4 nanoparticles

High-entropy oxide (HEO) has recently become popular because of its unique multifunctional performance. In this study, we developed a novel microwave-assisted method for the production of HEO nanoparticles with the composition (Cr_0.2Fe_0.2Mn_0.2Co_0.2-xNi_0.2Zn_x)₃O₄ (x = 0, 0.05, 0.1, and 0.2). The results revealed that all metallic elements were uniformly distributed throughout the single-phase cubic spinel structure of the HEO nanoparticles. The particle size distributions of four fabricated samples ranged from 10 to 50 nm. Because of its numerous advantages such as the ultrafast and low-temperature fabrication of nanoscale and high-purity products at a relatively low cost, the suggested methodology is an excellent synthesis method. The original HEO spinel (x = 0) achieved saturated magnetization (M_s) and coercivity (H_c) values of 24.3 emu/g and 160 Oe, respectively, at room temperature. Zinc substitution in the HEO composition indicated that M_s and H_c decreased with increasing zinc concentration owing to its non-magnetic nature.     

A medium-entropy perovskite oxide La0.7Sr0.3Co0.25Fe0.25Ni0.25Mn0.25O3-δ as intermediate temperature solid oxide fuel cells cathode material

In this study, we report a novel medium-entropy perovskite oxide of La_0.7Sr_0.3Co_0.25Fe_0.25Ni_0.25Mn_0.25O_3-δ (LSCFNM73) with high constitutive entropy (S_config) as the cathode material of intermediate temperature solid oxide fuel cells (IT-SOFCs). The intrinsic properties of phase structure, electrical conductivity, thermal expansion and oxygen adsorption capacity of La_1-xSr_xCo_0.25Fe_0.25Ni_0.25Mn_0.25O_3-δ (LSCFNM, x = 0, 0.1, 0.2, 0.3) oxides are evaluated in detail. The LSCFNM73 oxide exhibits the maximum electrical conductivity of 464 S cm⁻¹ at 800 °C and a relatively lower thermal expansion coefficient (TEC) of 15.34 × 10⁻⁶ K⁻¹, which is selected as the propriate cathode composition. The B-site of LSCFNM73 contains four elements which can increase the configuration entropy. Additionally, NiO-Yttria stabilized zirconia (YSZ) supported fuel cell is fabricated by tape casting, hot pressing-lamination, co-sintering and screen printing technologies. The fuel cell demonstrates a maximum power density of 1088 mW cm² at 800 °C, and excellent stability at 750 °C under 0.75V in 120 h and 10 times thermal cycling between 750 °C and 400 °C. Therefore, the medium-entropy LSCFNM73 oxide can be applied in IT-SOFCs as a competitive cathode material.     

Stabilizing the structure and suppressing the voltage decay of Li[Li0.2Mn0.54Co0.13Ni0.13]O2 cathode materials for Li-ion batteries via multifunctional Pr oxide surface modification

The development of Li-rich layer cathode materials has been limited by poor cycle, rate performance, phase transformation and voltage decay. To improve these properties, a facile and low-cost wet method is employed to fabricate Pr₆O₁₁ coating layer on Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles. The 3–6 nm Pr₆O₁₁ coating layer is observed on the surface of Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ by HRTEM. Interestingly, HAADF-STEM and EDS analyses show that the transition metal ions and the praseodymium ions mutually infiltrate in the Pr₆O₁₁ coating layer and Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles during calcination. A combination of HAADF-STEM with EDS and XPS studies reveals that Pr₆O₁₁ coating layer is bridged to Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles by the chemical bonds of transition phase Li_1.2M_XPr_1−xO₂. XRD patterns show that all samples are indexed to the layered structure α-NaFeO₂, but the lattice parameters are influenced lightly after Pr₆O₁₁ coating. HRTEM and SAED analyses elucidate that the super large Pr ions surface-doping and the Pr₆O₁₁ coating are verified to suppress the transformation of layer to spinel structure in the bulk nanoparticles after cycles. The sample coated with 3 wt% Pr₆O₁₁ exhibits wonderful electrochemical performance with the first coulomb efficiency of 85.6%, the capacity retention ratio of 97.9% after 50 cycles and the discharge capacity of 162.2 mAh g⁻¹ at 5 C. The resistant of charge transfer and the electrodes polarization are reduced by Pr₆O₁₁ coating according to EIS. Therefore, Pr₆O₁₁, which contains the super large Pr ions, plays two roles: the first one, it is coated on the Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles to optimize the environment of the interface reaction between electrodes and electrolyte; the other one, its Pr ions surface-doping stabilizes the structure in the superficial region of Li[Li_0.2Mn_0.54Co_0.13Ni_0.13]O₂ nanoparticles and suppresses the voltage decay. The multifunctional Pr₆O₁₁ can play a significant role in accelerating development of new materials with excellent stabilization and high capacity.     

Tuning Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode to high stability and activity via Ce-doping for ceramic fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) fuel-cell cathode stands out because of its ultrahigh ionic conductivity and excellent electrocatalytic activity, but it is still very subject to instability. Here, a new strategy of Ce doping is proposed to boost the stability and activity of the BSCF cathode. A one-pot combustion method is employed to synthesize (Ba_0.5Sr_0.5)_1–xCe_xCo_0.8Fe_0.2O_3-δ (x=0–0.2) cathodes. Both BSCF and (Ba_0.5Sr_0.5)_0.9Ce_0.1Co_0.8Fe_0.2O_3-δ have a cubic perovskite structure. (Ba_0.5Sr_0.5)_0.8Ce_0.2Co_0.8Fe_0.2O_3-δ shows two phases of cubic perovskite and fluorite ceria. Proper Ce doping can boost the electrical conductivity of BSCF, and can dramatically reduce the polarization resistance of BSCF cathode. Ce doping significantly improved BSCF cathode long-term stability by 160 h. Moreover, ten-percent Ce doping in BSCF highly improves single-cell output performance from 516.33 mW cm^?2 to 629.75 mW cm^?2 at 750 °C. The results reveal that Ce doping as a potential strategy for enhancing the stability and activity of BSCF cathode is promising.     

Preparation and formation mechanism of Cr-free spinel-structured high entropy oxide (MnFeCoNiCu)3O4

In this work, two Cr-free high entropy oxides (HEOs), an equimolar (MnFeCoNiCu)₃O₄ and a non-equimolar (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ have been synthesized by a solid-state reaction method. The reaction sequence and electrical conductivity were also studied for these two HEOs. It is demonstrated that a rock-salt phase containing a solid solution of NiO and CuO appears in the synthesizing process of (MnFeCoNiCu)₃O₄, which is ascribed to the incomplete solubilization of rock-salt phase in the spinel phase. For (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄, a single spinel phase (Fd-3m) is obtained at 750 °C, which is much lower than that of the (MnFeCoNiCu)₃O₄ sample. Furthermore, Mn, Fe, Co, Ni elements exist in the chemical states of +2 and + 3, and Cu exists in Cu²⁺ state. The electrical conductivity of (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ is approximately 15.77 S cm^-1 at 800 °C, which is nearly three times higher than that of the (MnFeCoNiCu)₃O₄ sample.     

The effect of AlF3 modification on the physicochemical and electrochemical properties of Li-rich layered oxide

Lithium (Li)-rich layered oxides are considered promising cathode materials for Li-ion batteries because of their favorable properties. Here, we report our recent finding in the novel oxide, aluminum fluoride (AlF₃)-modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCAF), which was synthesized via a facile, cost-effective and readily scalable solid-state reaction. LMNCAF possess an F and Al co-doped core structure with a LiF nano-coating on its surface which leads to considerably enhancement in the electrochemical performance of the oxide. The initial discharge capacity (at 0.05 C) increased from 212 mA h g⁻¹ for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to 291 mA h g⁻¹ for LMNCAF. A much higher discharge capacity of 211 mA h g⁻¹ was obtained for LMNCAF after 99 charge/discharge cycles at 0.2 C compared with that of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (160 mA h g⁻¹). Our preliminary results suggest that AlF₃ modification is an effective strategy to tailor the physicochemical and electrochemical properties of Li-rich layered oxides.     

Chemical synthesis of Co and Mn co-doped NiO nanocrystalline materials as high-performance electrode materials for potential application in supercapacitors

Co and Mn co-doped with NiO nanostructued materials, such as, Ni_0.95Co_0.01Mn_0.04O_1−δ, Ni_0.95Co_0.04Mn_0.01O_1−δ and Ni_0.95Co_0.025Mn_0.025O_1−δ were synthesized by chemical synthesis route and studied for potential application as electrode materials for supercapacitors. The phase structure of the materials was characterized by X-ray diffraction (XRD) and the crystallographic parameters were found out and reported. FTIR (Fourier Transform Infrared) spectroscopy revealed the presence of M–O bond in the compounds. The particle size of the materials was found to be in the range of 291.5–336.5 nm. The morphological phenomenon of the materials was studied by scanning electron microscopy (SEM) and the particles were found to be in spherical shape with average grain size of 14–28 nm. EDAX analysis confirmed the presence of appropriate levels of elements in the samples. The in-depth morphological characteristics were also studied by HR-TEM (High Resolution Tunneling Electron Microscopy). Cyclic voltammetry, chronopotentiometry and electrochemical impedance measurements were applied in an aqueous electrolyte (6 mol L⁻¹ KOH) to investigate the electrochemical performance of the Co and Mn co-doped NiO nanostructured electrode materials. The results indicate that the doping level of Co and Mn in NiO had a significant role in revealing the capacitive behaviors of the materials. Among the three electrode materials studied, Ni_0.95Co_0.025Mn_0.025O_1−δ electrode material shows a maximum specific capacitance of 673.33 F g⁻¹ at a current density of 0.5 A g⁻¹. The electrochemical characteristics of blank graphite sheet were studied and compared with the performance of Co/Mn co-doped NiO based electrode materials. Also, Ni_0.95Co_0.025Mn_0.025O_1−δ has resulted in a degradation level of 4.76% only after 1000 continuous cycles, which shows its excellent electrochemical performance, indicating a kind of potential candidate for supercapacitors.     

Development of La(CrCoFeNi)O3 system perovskites as interconnect and cathode materials for solid oxide fuel cells

The purpose of this research is to develop interconnect and cathode materials for use in solid oxide fuel cells (SOFCs) which demonstrate desired properties of outstanding sintering properties, high electrical conductivity, and excellent chemical stability at high temperatures. Five different perovskite oxides of lanthanum in combination with chromium, iron, cobalt and nickel oxides powders, i.e. LaCr_0.7Co_0.1Fe_0.1Ni_0.1O₃(LCr7CFN), LaCo_0.7Cr_0.1Fe_0.1 Ni_0.1O₃(LCo7CFN), LaFe_0.7Cr_0.1Co_0.1Ni_0.1O₃(LFe7CCN), LaNi_0.7Cr_0.1Co_0.1Fe_0.1O₃(LNi7CCF), and LaCr_0.25Co_0.25Fe_0.25Ni_0.25O₃(LCCFN), were synthesized through the Pechini method. XRD results show that all materials are in single phase, either rhombohedral or orthorhombic crystal structure. The resulting powders were able to be sintered to a high relative density at a temperature of 1400 °C for 2 h in air. The electrical conductivity of the sintered sample was measured and evaluated from 300 °C to 800 °C. The LCCFN sample appears to have the best combination of sintering property (approximate 94% relative density) and electrical conductivity (88.13 Scm⁻¹ at 800 °C).     

Significantly Enhanced Infrared Emissivity of LaAlO3 by Co‐Doping with Ca2+ and Cr3+ for Energy‐Saving Applications

In this study, Ca²⁺–Cr³⁺ co‐doped LaAlO₃, a novel energy‐saving material with significantly enhanced infrared emissivity, was synthesized by solid‐state reaction. The experimental results demonstrated that 20 mol% Ca²⁺ and 10 mol% Cr³⁺‐doped LaAlO₃, namely La_0.8Ca_0.2Al_0.9Cr_0.1O₃, had an infrared emissivity as high as 0.92 in the spectral region of 1–5 μm, which was 12 times higher than that of pure LaAlO₃. The first‐principles electronic structure calculations revealed that the Ca²⁺–Cr³⁺ co‐doping results in the occurrence of impurity energy levels in the forbidden band of LaAlO₃, which were mainly composed of the Cr 3d orbitals. Electrons partly occupied these impurity donor states and significantly reduced the energy bandgap, thus the infrared radiation property of LaAlO₃ was enhanced. This novel material with high infrared emissivity shows promising applications for energy‐saving in the field of thermal process equipment.     

Role of Mn doping on magnetic properties of multiferroic NiCr2O4 nanoparticles

The structural and magnetic properties of Mn doped Nickel Chromite (Ni_1-xMn_xCr₂O_4, x = 0, 0.2, 0.3, 0.4, 0.6, 0.8) nanoparticles (NPs) were studied in detail. The X-ray diffraction analysis affirms normal spinel structure for all the samples and average crystallite size was found in the range 31–58 nm. The spinel structure of these nanoparticles was also confirmed by Fourier transform infrared spectroscopy which revealed the formation of tetrahedral and octahedral vibrational bands in the range 607 -628 cm^?1 and 486 - 491 cm^?1, respectively. Transmission electron microscopy images depicts less agglomerated and non-spherical shaped NPs. The temperature dependent zero field cooled and field cooled magnetic measurements revealed a paramagnetic to ferrimagnetic transition T_c at 87 K for NiCr₂O₄ NPs, which is shifted to low temperatures by Mn doping. This effect was attributed to cationic distributions between adjacent sites produced by Mn doping. M ? H loops of Ni_1-xMn_xCr₂O₄ NPs revealed enhanced saturation magnetization with increase in Mn doping which is attributed to a large magnetic moment of Mn ions. Ni_1-xMn_xCr₂O₄ (x = 0.6 and 0.8) NPs show steps in their M ? H loops because of exchange interactions between two sites of these NPs.     

Synthesis and characterization of high-density non-spherical Li(Ni1/3Co1/3Mn1/3)O2 cathode material for lithium ion batteries by two-step drying method

Non-spherical Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders have been synthesized using a two-step drying method with 5% excess LiOH at 800 °C for 20 h. The tap-density of the powder obtained is 2.95 g cm⁻³. This value is remarkably higher than that of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders obtained by other methods, which range from 1.50 g cm⁻³ to 2.40 g cm⁻³. The precursor and Li(Ni_1/3Co_1/3Mn_1/3)O₂ are characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscope (SEM). XPS studies show that the predominant oxidation states of Ni, Co and Mn in the precursor are 2⁺, 3⁺ and 4⁺, respectively. XRD results show that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ material obtained by the two-step drying method has a well-layered structure with a small amount of cation mixing. SEM confirms that the Li(Ni_1/3Co_1/3Mn_1/3)O₂ particles obtained by this method are uniform. The initial discharge capacity of 167 mAh g⁻¹ is obtained between 3 V and 4.3 V at a current of 0.2 C rate. The capacity of 159 mAh g⁻¹ is retained at the end of 30 charge-discharge cycle with a capacity retention of 95%.     

La2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials with enhanced specific capacity and cycling stability for lithium-ion batteries

Li-rich layered oxides are the most promising cathode candidate for new generation rechargeable lithium-ion batteries. In this work, La₂O₃-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were fabricated via a combined method of sol-gel and wet chemical processes. The structural and morphological characterizations of the materials demonstrate that a thin layer of La₂O₃ is uniformly covered on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particles, and the coating of La₂O₃ has no obvious effect on the crystal structure of Li-rich oxide. The electrochemical performance of La₂O₃-coated Li-rich cathodes including specific capacity, cycling stability and rate capability has been significantly improved with the coating of La₂O₃. The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with 2.5 wt% La₂O₃ exhibits the highest discharge capacity, improved cycling stability and reduced charge transfer resistance, delivering a large discharge capacity of 276.9 mAh g⁻¹ in the 1st cycle and a high capacity retention of 71% (201.4 mAh g⁻¹) after 100 cycles. The optimal rate capability of the materials is observed at the coating level of 1.5 wt% La₂O₃ such that the material exhibits the highest discharge capacity of 90.2 mAh g⁻¹ at 5 C. The surface coating of La₂O₃ can effectively facilitate Li⁺ interfacial diffusion, reduce the structural change and secondary reactions between cathode materials and electrolyte during the charge-discharge process, and thus induce the great enhancement in the electrochemical properties of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials.     

Structural,spectral, dielectric and photocatalytic studies of Zr-Ni doped MnFe2O4 co-precipitated nanoparticles

In this study the Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles fabricated by co-precipitation technique were investigated. Thermo-gravimetric analysis (TGA) exhibited the annealing temperature of the nanoparticles ~990 °C. Cubic spinel structure of Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. Crystallite size was calculated by XRD data and found in the range of 32–58 nm. Photocatalytic activity of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄/graphene nanocomposites was tested by degrading methylene blue (MB) under visible light irradiation. The MB was almost completely degraded in the presence of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄-graphene nanocomposites under visible light irradiation. Dielectric parameters were also investigated in the frequency range 1×10⁶–3×10⁹ Hz. An overall decrease in the values of dielectric constant, dielectric loss and tangent loss was observed on account of the substitution of Zr and Ni with Mn and Fe cations.     

Multi-component strategy for remarkable suppression of thermal conductivity in strontium diyttrium oxide: The case of high-entropy Sr(Y0.2Sm0.2Gd0.2Dy0.2Yb0.2)2O4 ceramic

Anti-spinel oxide SrY₂O₄ has attracted extensive attention as a promising host lattice due to its outstanding high-temperature structural stability and large thermal expansion coefficient (TEC). However, the overhigh thermal conductivity limits its application in the field of thermal barrier coatings. To address this issue, a novel high-entropy Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ ceramic was designed and synthesized for the first time via the solid-state method. It is found that the thermal conductivity of Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ is reduced to 1.61 W·m⁻¹·K⁻¹, 53 % lower than that of SrY₂O₄ (3.44 W·m⁻¹·K⁻¹) at 1500 °C. Furthermore, reasonable TEC (11.53 ×10⁻⁶ K⁻¹, 25 °C ∼ 1500 °C), excellent phase stability, and improved fracture toughness (1.92 ± 0.04 MPa·m^1/2) remained for the high-entropy Sr(Y_0.2Sm_0.2Gd_0.2Dy_0.2Yb_0.2)₂O₄ ceramic, making it a promising material for next-generation thermal barrier coatings.     

A novel high-entropy monoboride (Mo0.2Ta0.2Ni0.2Cr0.2W0.2)B with superhardness and low thermal conductivity

A new high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic with a WB-type orthogonal structure was designed and synthesised by in-situ reactive hot pressing at 2000 °C and 30 MPa for 1.5 h under an argon atmosphere. The microstructure of the sintered samples was comprehensively characterised, and the formation of a high-entropy monoboride (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic was confirmed. Owing to the high density of the dislocations and strengthening metal-boron bonds, the high-entropy (Mo_0.2Ta_0.2Ni_0.2Cr_0.2W_0.2)B ceramic exhibited a hardness of 48.51 ± 4.07 GPa, which enabled it to be classed as a new superhard material. In addition, the thermal conductivity (2.05 ± 0.10 W/(m·K) at 400 °C) and electric conductivity (132.30 S/cm) were determined.