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The present investigation aims to synthesize a novel (AlCuCoFeMnNi)3O4 type high entropy spinel oxide through the sol‐gel and investigate the effect of different carbon‐based additives on charge storage performance. The formation of the inverse spinel phase of [B(AB)O4] type inverse spinel phase was confirmed through the detailed x‐ray diffraction analysis of the synthesized sample. The synthesized spinel phase was indexed with the space group of Fd−3m and has a lattice parameter of 8.2697 Å. The synthesized high entropy oxide (HEO) phase Ni, Co, and Fe coexists in +2 and +3 states. At the same time, Cu in +2 state, Al in +3 state, and Mn in +3 and +4 states confirmed through x‐ray photoelectron spectroscopy. The electrochemical charge storage performance of synthesized HEO was measured through the three‐electrode setup in 2 M KOH aqueous electrolyte solution in two different potential windows, such as −0.2 to 0.4 V and 0.0 to 0.5 V. Different carbon‐based conducting materials such as acetylene black, reduced graphene oxide (RGO), and carbon particles obtained from 10‐hour ball‐milling of used dry cell carbon electrode (CP). The charge storage mechanism changes from electrochemical double layer capacitance to pseudocapacitive type as the potential window varies from −0.2 to 0.4 to 0 to 0.5 V. The value of specific capacitance for an electrode made of HEO with acetylene black, RGO, and CP was found to be 32.67, 7.50, and 4.58 F/g and 30.68, 16.33, and 9.05 F/g in the potential window of −0.2 to 0.4 V and 0 to 0.5 V at a scan rate of 5 mV/s, respectively. The cyclic performance of the developed three electrodes was measured at a scan rate of 100 mV/s for 1000 cycles, and it was found to be 94%, 98%, and 99% for electrodes made of HEO with acetylene black, RGO, and CP, respectively. [ABSTRACT FROM AUTHOR]

The aim of the present study is to investigate the effect of synthesis routes on phase evolution, microstructure, change in ionic state and their co‐relation with electrochemical charge storage, and magnetic properties of novel (CuNiFeMnCo)3O4 high entropy spinel oxide (HESO). We successfully synthesized novel (CuNiFeMnCo)3O4 HESO through two different synthesis methods, that is, sol‐gel and reverse coprecipitation methods abbreviated as SA‐1 and SA‐2, respectively. The XRD analysis for both samples reveals the formation of inverse spinel phase (space group Fd‐3m) with the lattice constant of 8.3602 and 8.2502 Å for SA‐1 and SA‐2, respectively. The sample synthesized through the sol‐gel method possessed porous morphology, whereas the sample synthesized through the reverse coprecipitation method had spherical particles. The x‐ray photoelectron spectroscopy confirmed the presence of +2 and +3 ionic states for Fe, Ni, and Co, while Cu has a + 2 state and Mn exist in +3 and +4 states for both the synthesized samples. The ionic states of all cations remain invariant irrespective of the synthesis methods. However, the concentration of oxygen vacancy is significantly different for samples synthesized through different routes. Both the HESO electrodes show the electrochemical double‐layer capacitive type behavior in 2 M KOH electrolytic solution. The value of maximum specific capacitance is 38.46 and 34.24 F/g at a scan rate of 5 mV/s for SA‐1 and SA‐2, respectively. Moreover, the electrodes have capacity retention of 90 and 99% for 1000 cycles at a scan rate of 50 mV/s for SA‐1 and SA‐2, respectively. The magnetic property of the synthesized HESO samples was also investigated, and the found values of magnetization and coercivity are 1.79 emu/g and 54.9 Oe and 8.5 emu/g and 67.69 Oe for SA‐1 and SA‐2, respectively. [ABSTRACT FROM AUTHOR]

The novel (CuNiZnAlFe)3O4 type nanocrystalline High Entropy Oxide (HEO) was synthesized through the sol‐gel method with combustion at 350°C for 1 h duration. The XRD analysis reveals the formation of inverse spinel [B(AB)O4] type phase indexed with the space group of Fd‐3 m confirmed through the Rietveld Refinement of the XRD data. The lattice constant for the synthesized spinel phase was found to be 8.2453°A. The Scanning Electron Microscope of the synthesized HEO confirms the flakes‐like morphology with porous microstructure. The Energy Dispersive X‐ray (EDX) analysis and elemental mapping confirm the homogeneous distribution of the cations over the selected region. It was found that Fe and Ni are in the +3 and +2 states, other cations, Cu and Zn, are in the +2 states, and Al is in the +3 confirmed through the X‐ray photoelectron Spectroscopy. The electrochemical performance was studied in three electrodes in a 2 M KOH aqueous electrolyte. The specific capacitance value was 2.02, 1.58, 1.24, 1.06, 0.87, 0.71, and 0.65 F/g at scan rates of 5, 10, 20, 30, 50, 80, and 100 mV/s, respectively. The low value of specific capacitance was observed due to the stable ionic structure of the inverse spinel phase. The magnetization behavior of the sample is also investigated. The M‐H loop of the (CuNiZnAlFe)3O4 HEO sample exhibits a ferrimagnetic nature. [ABSTRACT FROM AUTHOR]

A mixture of spinel and rock-salt phase was synthesized for (Cu-Zn-Ni-Mg-Fe)O HEO High Entropy Oxide (HEO) through the modified solid-state synthesis and studied for the dielectric properties. Three different (Cu-Zn-Ni-Mg-Fe)O HEO samples were synthesized by the variation of synthesis parameters, i.e., 10 hour (hr) ball-milling followed by sintering at 1050 °C for 20 hr (10BM-HEO-20), 20 hr ball-milling followed by sintering at 1050 °C for 20 hr (20BM-HEO-20) and sintering for 10 hr (20BM-HEO-10) separately. The synthesized samples were studied for the effect of synthesis parameters on phase evolution and their correlation with dielectric properties. The volume phase fraction for the spinel and rock-salt phase changed with the variation of the synthesis parameters. The value of dielectric constant decreased for the sample 10 BM-HEO-20, 20BM-HEO-20 and 20 BM-HEO-10 HEOs due to the synergistic effect of decrease in particle size, volume phase fraction of spinel phase as well as more distorted unit cells of spinel HEO phase. The value of dielectric loss is in decreasing trend for 10BM-HEO-20, 20BM-HEO-20 and 20BM-HEO-10 samples. The value of the dispersion factor for 10BM-HEO-20, 20BM-HEO-20, and 20BM-HEO-10 are found to be 1.839, 2.313, and 2.156, respectively. The present study provides insight the dielectric properties of HEO can be tuned broadly by the change in the synthesis parameters. [ABSTRACT FROM AUTHOR]

In this report, a modified solid-state synthesis technique is optimized to synthesize a single spinel phase for a novel (CuNiTiZnFe) 3 O 4 High Entropy Oxide (HEO) and studied for magnetic behavior. Three different approaches were adopted for the synthesis of pure spinel HEO. In the first approach, The initial mixture of constituent oxides was admixed, and sintered at 1050 °C for 20 h. For the second and third approaches, the mixture of constituent oxides was ball-milled for 2 h, and 10 h separately, followed by sintering at 1050 °C for 20 h. A small amount of undiffused constituent oxide peaks are present in both the first and second approaches. However, the sample synthesis through 10 h milling followed by sintering has single spinel (CuNiTiZnFe) 3 O 4 HEO phase. The single spinel HEO phase formation was confirmed through the le-Bail refinement. The lattice parameter for the well-fitted XRD pattern is 8.415161 A°. Further, the investigation was focused on the magnetic behavior of the single spinel HEO phase. The value of magnetization and coercivity is 16.11 emu/g and 10.66 Oe, respectively. The synthesized HESO has typical ferrimagnetic nature and has the second-highest value of Ms reported so far for HEOs. The ionic states of different cations present in the (CuNiTiZnFe) 3 O 4 HESO were also investigated through X-ray photoelectron Spectroscopy. XPS analysis reveals that Fe and Ni are in the +3 and + 2 states, Cu and Zn are in the +2 states, and Ti is in the +4 states. [ABSTRACT FROM AUTHOR]

The present study reports the synthesis of a novel (Al 0·2 Co 0·2 Fe 0·2 Ni 0·2 Ti 0.2) 3 O 4 high entropy oxide (HEO) through the solid-state reaction method and its structural, dielectric, electric, and magnetic properties. For the first time, a cumulative study of dielectric, electric, and magnetic properties of the spinel HEO has been investigated in detail. The obtained HEO has a single-phase spinel structure with Fd-3m space group, confirmed through X-ray diffraction and Raman spectroscopy techniques. Moreover, Raman spectroscopic analysis also confirms that the synthesized spinel HEO is an inverse spinel. The dielectric and magnetic characterizations reveal a better dielectric permittivity of ε ′ = 35 at 1 MHz and high saturation magnetization Ms = 8.58 emu/g with low magnetic coercivity. The leakage current characteristics studied in terms of J-E curves indicate an ohmic conduction mechanism at a low electric field. Moreover, the high dielectric permittivity with resistive switching behavior (observed in the J-E curve) indicates its potential application in resistive switching memory devices, which have better functionality and enhanced scalability. [Display omitted] • Novel single-phase inverse spinel structured (Al 0.2 Co 0.2 Fe 0.2 Ni 0.2 Ti 0.2) 3 O 4 HEO is synthesized by the solid-state method. • Cumulative study of dielectric, electric, and magnetic properties of the spinel HEO reported for the first time. • Synthesized HEO showed resistive switching behavior in the J-E curve and yielded better dielectric and magnetic properties. [ABSTRACT FROM AUTHOR]