Solid-state synthesis of heterogeneous Ni0.5Cu0.5-xZnxFe2O4 spinel oxides with controlled morphology and tunable dielectric properties

Heterogeneous Ni 0.5 Cu 0.5− x Zn x Fe 2 O 4 (0.0 ≤ x ≤ 0.5) nanoparticles are prepared via a green, solventless and additive-free, soft mechanochemical process at room temperature. This solid-state synthetic procedure yields ternary and quaternary oxide nanoparticles with uniform morphology (average particle size: 104–136 nm). X-ray diffraction analyses of Ni 0.5 Cu 0.5− x Zn x Fe 2 O 4 nanoparticles reveal a cubic spinel structure with crystallite size in the range of 24–31 nm. The lattice parameter ( a ) and hopping length for tetrahedral ( L A ) and octahedral ( L B ) lattice sites are found to increase with the increase in Zn 2+ content, while X-ray ( ρ xrd ) and bulk ( ρ bulk ) densities decrease slightly due to increasing lattice volume. Ni 0.5 Cu 0.5− x Zn x Fe 2 O 4 nanoparticles with ( x = 0.2, 0.3, 0.4) exhibit excellent dielectric performance with high permittivity (ε̍ = 92–111) and suppressed dielectric loss (ε̎ = 1.8–2.8) at high frequency (~ 10 6 Hz). The polarization mechanism is discussed, involving major contributions from the electron hopping (Fe 2+ ↔ Fe 3+ ) at the octahedral sites. The influence of Cu 2+ and Zn 2+ concentration on the cationic distribution and dielectric performance is analyzed. The electrical conductivity is found to follow the power law ( σ ac = Aω n ) with n = 0.7, which confirms the ac conduction phenomenon driven by the electron hopping mechanism. The dielectric behavior of Ni 0.5 Cu 0.5− x Zn x Fe 2 O 4 nanoparticles reveals their potential for applications in high-frequency microwave devices.