Nanostructured ZnFe2O4: An Exotic Energy Material

Abstract

More people, more cities; the energy demand increases in consequence and much of that will rely on next-generation smart materials. Zn-ferrites (ZnFe₂O₄) are nonconventional ceramic materials on account of their unique properties, such as chemical and thermal stability and the reduced toxicity of Zn over other metals. Furthermore, the remarkable cation inversion behavior in nanostructured ZnFe₂O₄ extensively cast-off in the high-density magnetic data storage, 5G mobile communication, energy storage devices like Li-ion batteries, supercapacitors, and water splitting for hydrogen production, among others. Here, we review how aforesaid properties can be easily tuned in various ZnFe₂O₄ nanostructures depending on the choice, amount, and oxidation state of metal ions, the specific features of cation arrangement in the crystal lattice and the processing route used for the fabrication.

Keywords: energy harvesting and storage; inverted ZnFe2O4; nanostructuration.

Figure 1

Atomic structure of the spinel zinc ferrite with (a) normal and (b) inverse cation distributions. In each case, the conventional cubic cell (with 8 f.u. of ZnFe₂O₄) is delimited by solid black lines. Tetrahedral (A) and Octahedral (B) atomic coordination environments can also be identified by their polyhedra. Orange, green, and red atoms correspond to Zn, Fe and O chemical elements, respectively.

Figure 2

The spin magnetic moment per formula unit of Zn_yFe_3−yO₄ for y = 0 and 1.

Figure 3

Magnetic moment, Yafet–Kittel angles, and resistivity as a function of y in Zn_yFe_3−yO₄ at 300 K (Reproduced with permission from [17]. Copyright American Physical Society, 1976).

Figure 4

Spin-projected densities of states (DOS) of the Zn_yFe_3−yO₄ bulk compound obtained from the DFT calculations, using a GGA+U (U(Fe,3d) = 4.0 eV) approximation. (a) y = 0 corresponds to the half-metallic and ferrimagnetic magnetite Fe₃O₄ and (b) y = 1 to the insulating and antiferromagnetic ZnFe₂O₄. Positive and negative DOS represent, respectively, the projection onto majority and minority spin states.

Figure 5

(a) Low-magnification TEM image of ZnFe₂O₄ nanoparticles of average size 11 nm. (b) Cation inversion and lattice parameter, Ms and crystalize at different annealing temperatures (Reproduced with permission from [40]. Copyright American Chemical Society, 2019). (c) Degree of inversion, x, versus the annealing temperature comparison of result with values obtained by different groups (Reproduced with permission from [42]. Copyright PCCP Owner Societies, 2018). (d) UV-diffuse reflectance spectrum of ZnFe₂O₄ nanoparticles with increasing degree of inversion (— x = 0.074;  x = 0.104;  x = 0.134;  x = 0.159;  x = 0.203).

Figure 6

(a) TEM images of ZFPLD1 films grown at T_S of RT, 350 °C and 850 °C exhibit their nanocrystalline nature (b) Room-temperature spontaneous magnetization (4πMs) values vs. grain sizes in ZFPLD1, ZFPLD2, and ZFRF films (Reproduced with permission from [39]. Copyright AIP Publishing, 2006). (c) Absorption coefficient of ZFPLD1 films with grain size of ~35 nm (full line) and ~70 nm (dashed line). Corresponding imaginary part of permittivity are plotted in the Inset (Reproduced with permission from [14]. Copyright AIP Publishing, 2015).

Figure 7

(a) Variation of room temperature resistivity (Ω-cm) and (b) saturated magnetization (emu/mm³) of Zn_yFe_3−yO₄ thin films with oxygen pressure, P(O₂) and substrate temperature, T_S, respectively. (c) Comparison between thermodynamic equilibrium lines (the amount of Fe²⁺) and resistivity variation trend (Reproduced with permission from [44]. Copyright AIP Publishing, 2007).

Figure 8

(a) Change in the c-axis lattice parameter of Zn_yFe_3−yO₄ thin film grown in pure Ar atmosphere (squares) and an Ar/O₂ mixture (circles) with Zn content y. (b) Correlation between saturation magnetization M_S and conductivity σ_xx (Reproduced with permission from [46]. Copyright American Physical Society, 2009).

Figure 9

(a) High-resolution TEM of Zn₀.₃Fe₂.₇O₄ nanospheres (Reproduced with permission from [52]. Copyright American Physical Society, 2019). (b) SEM images of nanotubes in the lower panel and SEM images of nanobelt in the upper panel (Reproduced with permission from [58]. Copyright Elsevier, 2018). (c) SEM images of hollow porous core-shell ZnFe₂O₄/AgCl nanocube (blue dotted line represents cubic facet) coated with EDTA-Ag nanoparticles (Reproduced with permission from [59]. Copyright Elsevier, 2020).

Figure 10

(a) M-H loops of SrFe₁₂O₁₉/ZnFe₂O₄ with molar ratio 5 (Reproduced with permission from [61]. Copyright Elsevier, 2018). (b) Variation of Ms and Hc values with molar ratio changing from 5 to 0.2. (c) M-H loops of SrFe₁₂O₁₉/ZnFe₂O₄ with normal structured ZnFe₂O₄ (Reproduced with permission from [62]. Copyright Elsevier, 2013). (d) M-H loops of exchange-coupled CoFe₂O₄/ZnFe₂O₄ bilayer at 10 K (Reproduced with permission from [60]. Copyright AIP Publishing, 2013).

Figure 11

(a) Schematic of spin valve with the ferroelectric anti-ferromagnet BFO as the pinning layer and the proposed materials for other epitaxial layers. (b) M-H loops recorded upon heating up. The sample was annealed at H_ann = 3 kOe from 400 °C to room temperature before the measurements. The arrow indicates the direction of H_ann. (c) Temperature dependence of the exchange bias (H_ex) and saturation magnetization (Ms). (d) The MR measured in such a spin valve heterostructures (Reproduced with permission from [64]. Copyright Elsevier, 2013).

Figure 12

Schematic of inductor coil on a Si-CMOS chip (a) with passivation removed from 3-sides of the coil, and (b) with ZnFe₂O₄ thin (250 nm) film-coated conformally; (c,d) show the SEM images of the coil before and after ferrite coating; (e) Measured inductance and Q-factor of the on-chip inductance with ferrite film deposited only on top (in red) and surrounding 3-sides of the coil (in green) (Reproduced with permission from [55]. Electrochemical Society, 2017).

Figure 13

Structures of (a) Li₀.₅ZnFe₂O₄, (b) LiZnFe₂O₄, and (c) Li₂ZnFe₂O₄. (grey with a yellow circle: Zn⁺² ions in 8a site) (Reproduced with permission from [74]. Copyright American Chemical Society, 2017).

Figure 14

(a) TEM image of ZnFe₂O₄. (b) Cycle performances and Coulombic efficiencies (CE) of ZnFe₂O₄ at a current density of 100 mA g⁻¹ (Reproduced with permission from [77]. Copyright Royal Society of Chemistry, 2015). and (c) SEM image of ZFPE-15 and (d) cycle performances and Coulombic efficiencies (CE) at a current density of 1A g⁻¹ (Reproduced with permission from [86]. Copyright Elsevier, 2020).

Figure 15

(a) Schematic of electrolysis cell for water splitting, (b) current density J vs. potential curves, V of ZnFe₂O₄ photoanodes (Reproduced with permission from [92]. Copyright Royal Society of Chemistry, 2017). (c,d) TEM image of ZnFe₂O₄-Al₂O₃ and corresponding J vs. V curves (Reproduced with permission from [93]. Copyright Royal Society of Chemistry, 2018). (e) SEM images ZnFe₂O₄ nanorod, ZFO-500 (f) J vs. V curves (Reproduced with permission from [95]. Copyright Wiley, 2018).

Figure 16

Hydrothermal method: (a) SEM images of ZFO precursor nanowall arrays on CT fibres, (b) specific capacitances as a function of scan rate, and (c) comparative Ragone plots (Reproduced with permission from [98]. Copyright Elsevier, 2019). In-situ bio-mediated green rotational chemical bath deposition: (d) TEM of ZnFe₂O₄ nano-flakes@ZnFe₂O₄/C nanoparticle thin film heterostructure, (e) plot of specific capacitance (F g⁻¹) vs. current density (mA cm⁻²) and (f) Ragone plot (Reproduced with permission from [99]. Copyright American Chemical Society, 2017).