Unravelling cation distribution and its role in tuning the magnetic and dielectric properties of V-modified cuprospinel

In this work, CuFe2-xVxO4 (0 ≤ x ≤ 0.30) spinels were synthesized by sol-gel route to investigate the influence of V incorporation on the crystal structure, magnetic behaviour, dielectric response, and charge transport mechanisms in CuFe2O4. X-ray diffraction patterns confirm the formation of single phase tetragonal spinels with I41/amd symmetry, where increasing V content leads to lattice contraction and a systematic reduction in tetragonality. X-ray Photoelectron Spectroscopy establishes the presence of Cu2+, Fe3+/Fe2+, and V3+ cations and indicates that the cation distribution becomes partially inverse, with the degree of inversion varying systematically with V content. Magnetic measurements reveal ferrimagnetic ordering for all compositions, with transition temperature decreasing from 835 K (x = 0) to 719 K (x = 0.30) as V3+ substitution weakens the A - O - B superexchange interactions. A secondary magnetic anomaly associated with Jahn-Teller distortion appears at 659 K in the parent compound (x = 0) and it decreases gradually upon V substitution. The saturation magnetization exhibits a slight enhancement up to x = 0.10 and then decreases at higher V levels. Dielectric and AC conductivity studies indicate that charge transport is governed predominantly by hopping across Fe2+ ↔ Fe3+ ions. V incorporation enhances the dielectric constant and reduces the activation energy for conduction. The temperature variation of frequency exponent suggests a crossover from overlapping large polaron tunnelling at low V concentration to a mixed non-overlapping small polaron tunnelling and correlated barrier hopping mechanism at higher x value. Mott Variable-range hopping analysis further indicates an increased density of localized states and reduced disorder, consistent with improved charge transport.