Solid-state synthesis of heterogeneous Ni_(0.5)Cu_(0.5-x)Zn_xFe_2O_4 spinel oxides with controlled morphology and tunable dielectric properties

摘要

Heterogeneous Ni_(0.5)Cu_(0.5-x)Zn_xFe_2O_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_xFe_2O_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_xFe_2O_4 nanoparticles with (x = 0.2, 0.3, 0.4) exhibit excellent dielectric performance with high permittivity (ε = 92-111) and suppressed dielectric loss (ε= 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_xFe_2O_4 nanoparticles reveals their potential for applications in high-frequency microwave devices.