Mechanical activation as a strategy for energy-efficient solid-state synthesis of Zn₂SnO₄ functional oxides

The effect of mechanical activation on the thermally assisted solid-state formation of Zn₂SnO₄ from ZnO and SnO₂ precursor powders was investigated. Mechanical activation was performed in a SPEX mill for up to 60 min, and the resulting powders were characterized by XRD, FEG-SEM, and TEM analyses. The kinetic behavior of Zn₂SnO₄ formation was analyzed using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, while activation energy (E_a) values were determined from Arrhenius plots. Mechanical activation significantly enhanced the formation kinetics of Zn₂SnO₄, reducing E_a from 277 to 54 kJ mol−1 and enabling phase formation at lower temperatures and shorter dwell times, which implies a reduction in the thermal energy input required for the solid-state reaction. This improvement can be attributed to an increased defect density, larger surface area, and enhanced interfacial contact between oxides induced by milling, promoting a transition from diffusion-controlled to interface-controlled growth. TEM analysis revealed the presence of Zn₂SnO₄ and Zn₂SnO₃ nanocrystals formed during milling, indicating that nucleation occurs prior to thermal treatment. Although the crystal structure remains unchanged (cubic inverse spinel Zn₂SnO₄), mechanical activation induces microstructural refinement, producing smaller crystallites (∼51 nm vs. ∼73 nm) and finer particle morphologies, which may enhance surface reactivity. These results demonstrate that mechanical activation is an effective strategy to accelerate solid-state reactions while improving the microstructural characteristics of functional oxide materials.