The rational construction and design of supercapacitors (SCs) with electrochemically favorable structural configuration and appreciable cyclic performances are highly demanding. Herein, a novel Ga-based transition metal oxide, NiGa 2 O 4 , was synthesized via sol−gel self-ignition techniques to design an advanced electrode for supercapacitor and field emitter applications. Reitveld refinement of XRD, FTIR, and Raman spectra reveals a larger cubic parameter due to the incorporation of Ga over NiO, which promotes faster charge kinetics and various metal oxide (Ni−O and Ga−O) stretching vibrations in the molecular fingerprint. Reduced graphene oxide (r-GO) with an enlarged surface area has been utilized as a conductive substrate to prevent the aggregation of NiGa 2 O 4 nanoparticles. The NiGa 2 O 4 electrodes exhibit a specific capacitance of 415 F g −1 at a current density of 1.5 A g −1 with capacitance retention of 74.2% at a current density of 20 A g −1 , in addition to outstanding cyclic performance over 3000 cycles (capacitance retention = 96.2%). R-GO-reinforced NiGa 2 O 4 electrodes (10:1) possess a higher specific capacitance of 643 F g −1 at a current density of 1.5 A g −1 in comparison to pristine NiGa 2 O 4 with 77.66% retentivity at a current density of 20 A g −1 , together with upgraded cyclic stability of 99.1% retentivity over 3000 cycles. The NiGa 2 O 4 /rGO field emitter delivers a low turn-on field of 4.42 V/μm@1 μA/cm 2 with a long field emission current stability of over 5 h in comparison to pristine NiGa 2 O 4 (turn-on field of 6.56 V/μm@1 μA/cm 2 ), which recommends it as a potential field emitter (FE) for vacuum micro-and nanoelectronics. Various FE parameters with field enhancement factor (β) are compared with those of other efficient field emitters. Experimental data were supported through theoretical insight from density functional theory (DFT) simulations. Enhanced quantum capacitance and increased density of states near the Fermi level contribute toward superior charge storage performance in r-GO-reinforced NiGa 2 O 4 compared to pristine NiGa 2 O 4 . The interaction between NiGa 2 O 4 and rGO involves charge transfer from NiGa 2 O 4 to the C 2p orbital. In addition, the reduction in work function for the hybrid structure justifies its improved field emission properties.
The electric field-induced sterling electron emission of NiMn2O4 microporous networks synthesized via the sol-gel auto combustion route was investigated. Some primary characterization techniques such as x-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy were performed to confirm the pure crystallinity and metal oxide (Ni–O and Cr–O) stretching vibrations and also to provide a molecular fingerprint of the NiMn2O4 porous network. The distinct field emission (FE) properties of the NiMn2O4 microporous network was observed which was correlated with an electric field induced electron tunneling F–N (Fowler–Nordheim) model from a nearly planner conducting emitter surface with triangular potential-energy barrier approximation. A low turn-on field of 4.15 V µm−1 and threshold field of 5.25 V µm−1 were detected to draw emission current densities of 1 µA cm−2 and 10 µA cm−2 respectively. The local work function (Φ) of 5.509 eV for the NiMn2O4 porous network was computed using density functional theory (DFT) and it exhibits an impressive field enhancement factor (β) of 3381 with good FE current stability. These results demonstrate the potential application of this material for future vacuum micro/nanoelectronics and FE panel display applications.
Microstructural NiO–SnO2 nano-ceramic matrix was synthesized via a solgel auto-combustion technique with a perspective to investigate its noteworthy electric field emission and temperature-induced conduction anomaly. Exceptional field emission performance of nickel-tin oxide composites was discovered with a low turn-on field of 3.9 V/μm and a threshold field of 5.30 V/μm with a good field emission current density of 110.44 μA/cm2 and current stability. Density functional theory was employed to estimate its local work function (Φ) 3.365 eV, and the field enhancement factor (β) was obtained as 1570 by Fowler–Nordheim plot. The anomalies in conductivity spectra at 523 K were detected by a number of physical properties measurement including impedance, conductivity, dielectric, and differential scanning calorimetry with thermal expansion. These phenomena can be rationalized in terms strain-dependent thermal hysteresis effects and localized/delocalized eg electron with a transition from inferior conductive linkage [Ni2+–O2−–Ni2+] and [Sn2+/Sn4+–O2−–Sn2+/Sn4+] to higher conductive linkage [Ni2+–Ni3+] and [Sn2+–Sn4+] of coupled NiO–SnO2 matrix. The temperature dependence frequency exponent (n), ln τ, Rg, Rgb, Cg, and Cgb support additionally the conduction anomaly behavior, and the variation of dielectric constant (ɛr) and loss (tan δ) with temperature around 523 K has been explained in terms of the reduction of space charge layers due to reversal movement of delocalized eg electrons from the grain boundary limit. The frequency dispersing impedance, conductivity, and dielectric spectra with elevated temperature were also demonstrated to comprehend its conduction mechanism with theoretical correlation.
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