Nanocrystalline ferrites NixZn1−xFe2O4: Influence of cation distribution on acidic and gas sensing properties

This work is devoted to a detailed analysis of the interconnection between composition, cation distribution and acidic properties of the surface of nanocrystalline ferrites NixZn1−xFe2O4 obtained by aerosol pyrolysis. The detailed analysis of the Mössbauer spectra allows us to determine the distribution of cations between tetrahedral and octahedral positions in spinel structure. Depending on samples composition, the tetrahedral positions can be occupied by only Fe3+ cations (inverse spinel, x≥0.4) or by Fe3+ and Zn2+ cations (mixed spinel, x=0, 0.2). Increasing the nickel concentration in the ferrite leads to decrease in the number of strong acid centers on the surface. It was found that the decrease in the contribution of strong surface acid sites leads to an increase in sensory sensitivity of the ferrite towards ammonia. For ethanol detection an inverse relationship between sensor signal and surface acidity was observed.

(a) n- and p-types change in electrical resistance and (b) sensor signal of NixZn1−xFe2O4 towards NH3 and ethanol vapor vs. the part of strong acid sites.Figure optionsDownload as PowerPoint slideHighlights
► Relationship between composition, cation distribution, and acidity in nanocrystalline NixZn1−xFe2O4.
► Degree of inversion of spinel is determined by Mössbauer spectroscopy.
► Increase of nickel content leads to decrease in the number of strong acid centers.
► This results in an increase in sensory sensitivity of the ferrite towards ammonia.
► Relationship between sensor signal to ethanol and surface acidity is opposite.