Optimization of switching charge and recoverable energy density mediated by structural transformation in Sr-substituted BaNiO3 perovskites.

Because of their distinctive characteristics, ferroelectric perovskites are considered among the most potent and auspicious candidates for energy storage and pulsed power devices. But their energy storage properties and switching capabilities need to be further enhanced which can be done by substitutions of appropriate cations. Hence, a series of lead-free Ba1-xSrxNiO3 (x = 0.00, 0.33, 0.67, and 1.00) ceramics was fabricated using a sol-gel auto combustion technique. Rietveld's refinement of X-ray diffraction plots verified the complete development of the required hexagonal perovskite structure. Scanning electron microscopy images revealed a gradual increase in average grain sizes and agglomeration with the increase in Sr-content. Moreover, the existence of all the constituent elements exactly in proportion to their stoichiometric ratios was verified by energy dispersive X-ray spectroscopy. The characteristic parameters of ferroelectric materials such as ferroelectric response, electrical conductivity, and switching charge density were also determined. The P-E loops indicated that with the increase in Sr-content, the coercive field, remanent polarization, and maximum polarization all decreased gradually, but the recoverable energy density (Wrec) increased as the loops became slimmer. The maximum value of Wrec was found in the Ba0.33Sr0.67NiO3 sample. Moreover, SrNiO3 exhibited minimum energy loss with the highest efficiency of ∼47.21%. The existence of a current barrier in all the samples was proved from the low leakage current values (∼10-7 A). In addition, the pure SrNiO3 showed a low electrical conductivity and minimum value of switching charge density. All these findings make SrNiO3 a promising candidate for fast switching and energy storage applications.

Elucidating an efficient super-capacitive response of a Sr2Ni2O5/rGO composite as an electrode material in supercapacitors.

Mixed transition metal oxides have emerged as efficient electrode materials because of their significant cycling stability, and superior capacitance values, resulting in remarkable electrochemical outputs. In this regard, Sr2Ni2O5/rGO composites were synthesized using a facile solvothermal method to achieve efficient electrochemical pursuits. X-ray diffraction confirmed the formation of finely crystallized samples with the phase evolution from orthorhombic to hexagonal. Morphological studies using field emission scanning electron microscopy depicted the desired porosity in samples with well-defined shapes and sizes of homogeneously distributed grains. Elemental analysis verified the pictorial depiction of sample compositions in terms of their stoichiometric ratios. The composite sample with composition Sr2Ni2O5@15%rGO exhibited superior electrochemical performance compared to other samples, depicting the highest specific capacitance of 148.09 F g-1 at a lower scan rate of 0.005 V s-1 observed via cyclic voltammetry. In addition, the cyclability performance of Sr2Ni2O5@15%rGO exhibits 68.5% capacitive retention after 10 000 cycles. The energy density as determined using a two-electrode system remained 4.375 W h kg-1 for the first cycle which reduced to 1.875 W h kg-1 for the 10 000th cycle, with a maximum power density of 1.25 W kg-1. The Nyquist plot represented less barrier to charge transfer. The electrode with particular composition Sr2Ni2O5@15%rGO emerged as significant, exhibiting a superior surface capacitive charge storage, that makes it a potential candidate as an electrode material.

Gateway toward efficient and miniaturized A 2 B 2O7-type fluorite structure-based energy storage devices.

Defect fluorite structure with A 2 B 2O7 composition exhibits an intense potential for utilization in modern smart electrical devices. Efficient energy storage with low loss factors like leakage current makes them a prominent candidate for energy storage applications. Here we report a series of the form Nd2-2x La2x Ce2O7 with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, synthesized via a sol-gel auto-combustion route. The fluorite structure of Nd2Ce2O7 is slightly expanded with the incorporation of La without any phase transformation. A gradual replacement of Nd with La causes a decrease in grain size, which increases the surface energy and thus leads to grain agglomeration. The formation of exact composition without any impurity element is confirmed by energy-dispersive X-ray spectra. The polarization versus electric field loops, energy storage efficiency, leakage current, switching charge density, and normalized capacitance, which are considered key features of any ferroelectric material, are comprehensively examined. The highest energy storage efficiency, low leakage current, small switching charge density, and large value of normalized capacitance are observed for pure Nd2Ce2O7. This reveals the enormous potential of the fluorite family for efficient energy storage devices. The temperature-dependent magnetic analysis exhibited very low transition temperatures throughout the series.

First-principles computational exploration of ferromagnetism in monolayer GaS via substitutional doping.

Using first-principles calculations, functionalization of the monolayer-GaS crystal structure through N or Cr-doping at all possible lattice sites has been investigated. Our results show that pristine monolayer-GaS is an indirect-bandgap, non-magnetic semiconductor. The bandgap can be tuned and a magnetic moment (MM) can be induced by the introduction of N or Cr atomic anion/cation doping in monolayer GaS. For instance, the intrinsic character of monolayer GaS can be changed by substitution of N for the S-site to p-type, while substitution of Cr at the S-site or Ga-site induces half-metallicity at sufficiently high concentrations. The defect states are located in the electronic bandgap region of the GaS monolayer. These findings help to extend the application of monolayer-GaS structures in nano-electronics and spintronics. Since the S-sites at the surface are more easily accessible to doping in experiment, we chose the S-site for further investigations. Finally, we perform calculations with ferromagnetic (FM) and antiferromagnetic (AFM) alignment of the MMs at the dopants. For pairs of impurities of the same species at low concentrations we find Cr atoms to prefer the FM state, while N atoms prefer the AFM state, both for impurities on opposite surfaces of the GaS monolayer and for impurities sharing a common Ga neighbor sitting at the same surface. Extending our study to higher concentrations of Cr atoms, we find that clusters of four Cr atoms prefer AFM coupling, whereas the FM coupling is retained for Cr atoms at larger distance arranged on a honeycomb lattice. For the latter arrangement, we estimate the FM Curie temperatureTCto be 241 K. We conclude that the Cr-doped monolayer-GaS crystal structure offers enhanced electronic and magnetic properties and is an appealing candidate for spintronic devices operating close to room temperature.

Electrochemical performance of Li+ insertion/extraction in Ni-substituted ZnCo2O4 as an emerging highly efficient anode material.

With the industrial revolution in electronics, the demand for lithium-ion batteries, particularly those designed for electric vehicles and energy storage systems, has accelerated in recent years. This continuously increasing demand requires high-performance electrode materials, as commonly used graphite anodes show limited lithium intercalation. In this context, Ni-substituted ZnCo2O4 nanostructures, thanks to their high storage capacity, have potential for use as an anode material in lithium-ion batteries. Structural analysis concludes that the prepared materials show improved crystallinity with increasing Ni at the Zn-site in ZnCo2O4. The intermediate composition, Zn0.5Ni0.5Co2O4, of this series exhibits a specific capacity of 65 mA h g-1 at an elevated current rate of 10 A g-1. The lithium insertion/extraction mechanism is investigated via cyclic voltammetry, showing two redox peaks from ZnCo2O4 and a single redox peak from NiCo2O4. Additionally, the lithium diffusion coefficient in the prepared electrodes is computed to be 2.22 × 10-12 cm2 s-1 for the intermediate composition, as obtained using cyclic voltammetry. Electrochemical impedance spectroscopy is used to observe the charge transport mechanism and the charge transfer resistance values of all the samples, which are calculated to be in the range of 235 to 306 Ω.

Physico-chemical properties and catalytic activity of the sol-gel prepared Ce-ion doped LaMnO3 perovskites.

Ce-doped LaMnO3 perovskite ceramics (La1-xCexMnO3) were synthesized by sol-gel based co-precipitation method and tested for the oxidation of benzyl alcohol using molecular oxygen. Benzyl alcohol conversion of ca. 25-42% was achieved with benzaldehyde as the main product. X-ray diffraction (XRD), thermogravimetric analysis (TGA), BET surface area, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), temperature-programmed oxidation (O2-TPO), FT-IR and UV-vis spectroscopic techniques were used to examine the physiochemical properties. XRD analysis demonstrates the single phase crystalline high purity of the perovskite. The Ce-doped LaMnO3 perovskite demonstrated reducibility at low-temperature and higher mobility of surface O2-ion than their respective un-doped perovskite. The substitution of Ce3+ ion into the perovskite matrix improve the surface redox properties, which strongly influenced the catalytic activity of the material. The LaMnO3 perovskite exhibited considerable activity to benzyl alcohol oxidation but suffered a slow deactivation with time-on-stream. Nevertheless, the insertion of the A site metal cation with a trivalent Ce3+ metal cation led to an enhanced in catalytic performance because of atomic-scale interactions between the A and B active site. La0.95Ce0.05MnO3 catalyst demonstrated the excellent catalytic activity with a selectivity of 99% at 120 °C.

Opto-electronic and thermoelectric properties of MgIn2X4 (X = S, Se) spinels via ab-initio calculations.

The structural behavior of MgIn2X4 (X = S, Se) has been elaborated by FP-LAPW + lo method as included in the Wien2k code. The stability of the phase has been confirmed by negative formation energy (-1.24 eV for MgIn2S4 and -0.78 eV for MgIn2Se4). The band gap dependent opto-electronic and thermoelectric properties are realized by modified Becke-Johnson exchange potential. The electronic band gap tuned from ultraviolet to visible (3.1 eV and 1.9 eV) by replacing the S with Se that motivated the studied spinels for photovoltaic and solar applications. Moreover, the attenuation of light, dispersion, transparency, reflection and energy loss when light scattered from material are discussed as function of energy. The thermal conductivity to electrical conductivity ratio, potential gradient and thermal efficiency in the range 0.78-0.80 are elaborated. The comparative study of opto-electronic and thermoelectric properties for energy harvesting increases the potential for optoelectronic than thermoelectric applications.

Synthesis and Characterization of BaTiO3/Polypyrrole Composites with Exceptional Dielectric Behaviour.

Higher concentrations of ceramic fillers induce brittleness in the ceramic/polymer hybrids which restrict their applications to limited fields especially when such hybrids are prepared for their use as dielectrics. We have synthesized and characterized different BaTiO3-polypyrrole (PPy) composites by changing the concentration of BaTiO3 from 1% by weight of PPy taken to 5 wt % to explore its effect on the dielectric parameters of the final product and found that the BaTiO3-polypyrrole composite with weight ratio of 0.05:1 exhibited highest dielectric constant, lowest dielectric loss and thermally most stable. All the composites were prepared using in-situ polymerization of pyrrole in an aqueous dispersion of low content of BaTiO3 in the presence of small amount of Hydrochloric acid. These composites were characterized for their microstructure and crystallinity by X-ray diffractometer (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) while thermal stability by thermo gravimetric (TGA) analysis. An impedance analyser (LCR meter) was utilized to investigate the dielectric parameters. FT-IR data confirmed the presence of the two phases and their interaction, inferred from the shifting of normal PPy peaks. The data obtained from XRD confirmed the presence of crystallites of 2.8 to 5 nm with dominant crystallinity of the filler, TGA analysis (25 to 600 °C) confirmed the higher thermal stability induced on successive addition of the filler into the prepared composites as compared to that of pure PPy in a wide temperature range which is unusual for such a low % age addition of the filler. The SEM analysis together with XRD results reveal that the successive introduction of BaTiO3 particles produced crystallites of 2 to 5 nm size which bonded together and changed the hemispherical shaped larger grains of the matrix to regular shaped smaller grains. The dielectric constant of the composites was enhanced with filler contents from 178 to 522 at 1 MHz for 1 wt % and 5 wt % BaTiO3 respectively. It was concluded that the introduction of BaTiO3 into the polymer matrix with this new procedure has greatly affected the polymerization process, thermal stability, morphology and dielectric properties of the host matrix and has resulted in a novel series of the composites which may have broad applications.