Porosity-controlled Y-doped Mg-Rb spinel ferrites: A new route toward efficient ceramic humidity sensors

This work presents the synthesis and characterization of yttrium‐doped magnesium–rubidium ferrite nanocrystalline ceramics, Mg₀.₉Rb₀.₁Y_xFe_2-xO₄ (x = 0.00–0.03), prepared via a fuel-assisted solution combustion method. X-ray diffraction confirms the formation of a single-phase cubic spinel structure, with the average crystallite size decreasing from ∼40.1 nm (x = 0) to ∼26.3 nm (x = 0.03), and a corresponding lattice parameter contraction from 8.383 Å to 7.950 Å. FTIR spectra show A-site and B-site metal–oxygen vibrations at ∼550–609 cm⁻¹and ∼380–450 cm⁻¹, respectively. The estimated elastic properties reveal composition-dependent variations in stiffness, with Poisson's ratio ranging from 0.25 to 0.275 and the Debye temperature increasing from ∼580 K to ∼630 K. SEM micrographs display agglomerated nanograins with interconnected pores, and the overall porosity lies between ∼12.1 and 19.0 %.The samples were evaluated as room-temperature humidity sensors across 11–97 % RH. The optimized composition (x = 0.03) exhibits a resistance variation of nearly four orders of magnitude and a maximum sensitivity of 99.99 %, with response and recovery times of ∼85 s and ∼5 s, respectively. Long-term testing confirmed stable performance over two months at 55 % and 97 % RH. The observed improvements are attributed to Y³⁺-induced lattice distortion, enhanced hydrophilicity, and facilitated proton transport via the Grotthuss mechanism. Overall, the tailored porosity and compositional design offer a promising route for high-performance ceramic humidity sensors suitable for ambient-condition applications.