Mössbauer Investigation of Molybdenum Trioxide-Hematite Nanoparticles

Molybdenum trioxide-doped hematite, xMoO₃*(1-x)α-Fe₂O₃ with molar concentrations x=0.1, 0.3, 0.5, and 0.7 was prepared using high-energy ball milling, taking samples at 0, 2, 4, 8, and 12 hours. The resulting Mössbauer spectra of nanoparticle systems were parametrized using NORMOS-90. At ball milling time (BMT) 0 hours, each concentration produced a spectrum consisting of 1 sextet since no lattice substitutions occurred. For all concentrations, a doublet subspectrum emerges from the initial sextet as the BMT increases. For each sample, this appears around BMT = 4 hours and is more intense as the BMT increases, indicating the substitution of Fe³⁺ into the MoO₃ lattice. Most fits only had 1 sextet except for concentration x =0.1, BMT 4, 8, and 12 hours, and concentration x=0.3, BMT 12 hours. This additional sextet indicates Mo was substituted into the Fe₂O₃ lattice. The absence of this Mo substitution is due to the difference in ionic radii of Mo⁶⁺ to Fe³⁺ since the ionic radius of Mo⁶⁺ is over twice the ionic radius of Fe³⁺. Since the substitution of Fe³⁺ into the MoO₃ was more present than the substitution of Mo⁶⁺ into Fe₂O₃, the solid solution has a limited mutual solubility.