Tunable multifunctionality in aliovalent substituted Bi12MnO20 sillenite for thermistor and other fascinating applications

A new aliovalent-substituted Bi₁₂MnO₂₀ sillenite is synthesized incorporating solid-state reaction route at optimized temperature 800°C. Structural analysis through Fullprof Rietveld refinement of XRD data confirmed a cubic I 23 structure with lattice and reliability parameters a = 10.105 Å and (R _p = 9.05%, R _wp = 15.95%, R _exp = 12.11% and χ ² = 1.74) respectively. The Williamson-Hall analysis indicated 1.344 nm crystallites and 0.0162 strain. The microstructural analysis through SEM displayed polycrystalline morphology with blocky, agglomerated grains with average grain size 255 nm. The color mapping of EDX spectra verified the expected elements in the system. The FTIR analysis gives the blueprint of sillenite vibrations in the wave number range 400–600 cm⁻¹. UV-Vis spectroscopy revealed strong 317 nm absorbance and a 2.31 eV direct bandgap in the synthesized sample. Dielectric responses followed the Maxwell-Wagner model, with temperature-activated polaron hopping, non-Debye relaxation, NTCR feature, and multi-interface contributions evident in Impedance/Modulus spectra. Conductivity adhered to Jonscher's power law, enhanced by aliovalent substitution with Mn at tetrahedral site. I-V characteristics confirmed n-type semiconducting behavior, with a thermistor coefficient β = 4157.3 K obtained through fitting Steinhart-Hart equation. Magnetic analysis features weak ferromagnetism with M _R = 0.005 emu/g, H _c = 115.84 Oe and M _s = 0.839 emu/g obtained via Grosinger's LAS model. These properties highlight potential of the synthesized sillenite material in UV photocatalytic, thermistors and magneto-electric devices oriented applications.