Mechanical alloying and thermal decomposition of (ZrO₂)_0.8-(α-Fe₂O₃)_0.2 powder for gas sensing applications

The mechanical alloying process of (ZrO₂)_0.8-(α-Fe₂O₃)_0.2 powder during high-energy ball milling at room temperature and the thermal decomposition of (ZrO₂)_0.8-(α-Fe₂O₃)_0.2 powder at high temperature were studied by XRD, TEM, and differential thermal analysis. It was found that monoclinic zirconia transforms to cubic zirconia stabilized by Fe³⁺ after a milling time of 60 h. With the increased milling time up to 120 h, the powder appeared to consist of amorphous-like conglomerates. This metastable compound decomposed at a temperature of 650°C. The expulsion of the α-Fe₂O₃ from the cubic ZrO₂ correlated directly with the current conductivity behavior and the oxygen gas sensing property of the thick film devices screen printed from this powder. The substitutional model Fe₂O₃⇆2Fe_Zr′ + V₀/^··+3O₀ was adapted to explain both the mechanical alloying and thermal decomposition processes.