Nanoscale Defect Modulation in Zn 1-x Ni x Fe 2 O 4 Spinel Nanoparticles: Hydrodynamic Agglomeration, Mesoporosity, and Coupled Magnetic and Electrochemical Responses
Year: 2026
Type: preprint
Abstract: Spinel ferrites (Zn 1−x Ni x Fe 2 O 4 ) exhibit adjustable magnetic and electrical properties, which are influenced by the distribution of cations between the tetrahedral and octahedral sites. XRD confirmed cubic spinel structure formation with systematic lattice contraction from 8.485 Å (x = 0.00) to 8.451 Å (x = 0.02), followed by a pronounced anomaly at x = 0.03 (a = 8.522 Å) and relaxation at x = 0.04 (8.462 Å). The x = 0.03 composition exhibited the minimum crystallite size (19.7 nm) and maximum microstrain (0.0058), consistent with the heightened defect density and cation redistribution. FTIR showed characteristic spinel bands (ν 1 = 547–550 cm − 1 , ν 2 = 451–460 cm − 1 ) and Kt > Ko (2.19–2.22×10 5 vs. 1.49–1.55×10 5 dyne/cm), alongside minor signatures of adsorbed water/CO 2 and trace amounts of PVA residues. The EIS Nyquist spectra displayed a single depressed semicircle dominated by grain boundaries; the fitted R gb peaked at 11119.0 Ω at x = 0.03 with non-Debye behavior (θ = 36.75°–44.73°, n up to 0.592), indicating maximal boundary scattering and suppressed Fe 2+ /Fe 3+ hopping. Despite nanoscale primary sizes, DLS revealed severe aqueous agglomeration (Z-average 3006–4539.9 nm; PDI 0.907–1.270), maximized at x = 0.03 (4539.9 nm; diffusion minimum 1.084×10 − 9 cm 2 /s), consistent with FE-SEM observations of porous spherical agglomerates formed via PVA combustion and gas evolution. Electrochemically, CV at 10 mV s − 1 showed a shift from an anodic peak (123.3 mV, 1.548 µA for x = 0.00) to cathodic-dominated redox (− 146.9 to − 338.6 mV) upon Ni substitution; specific capacitance dropped at x = 0.01, then increased to 6.47 and 6.24 mF g − 1 at x = 0.02 and 0.03 before declining to 3.14 mFg − 1 at x = 0.04, attributed to defect-rich mesoporosity and enlarged electroactive interface. VSM indicated soft ferrimagnetic/near-superparamagnetic behavior (Mr/Ms = 0.0033–0.0529) with a critical x = 0.03 hardening: Ms sharply decreased to 23.087×10 − 3 emu g − 1 , while Hc rose to 150.0 Oe and K to 1.732 erg g − 1 , implicating dead-layer spin canting and defect/grain-boundary pinning. Overall, a narrow compositional threshold near x = 0.03 maximizes the defect density and grain-boundary networks, simultaneously enhancing the coercivity and optimizing faradaic charge storage, establishing low-concentration Ni doping as an effective strategy to co-tune the magnetic functionality and electrochemical energy-storage performance in Zn-ferrite nanomaterials.
Source: Research Square
Institution: Holy Cross College
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204751981