Thermal decomposition of ZnO₂ to ZnO: driven by peroxide bond rupture and shear-induced stacking faults

This study investigates the thermal decomposition of cubic zinc peroxide (ZnO₂) into hexagonal zinc oxide (ZnO) through a combination of Rietveld refinement, bond valence analysis and high-resolution transmission electron microscopy (HRTEM). The decomposition begins around 140 °C accompanied by elongation and rupture of the peroxide bond (O-O), releasing oxygen. This bond rupture triggers a sequential shear displacement of the {111} lattice planes by ⅓〈112〉, generating stacking faults that alter the O-atom coordination from tricoordinate (O-3Zn) to tetracoordinate (O-4Zn). Consequently, the Zn-O bond valence increases from ⅓ to ½ v.u., necessitating a structural reconstruction from ZnO₆ octahedra to ZnO₄ tetrahedra and a phase transition from an ABCABC to an ABAB stacking sequence. This mechanistic pathway is directly corroborated by HRTEM imaging, which reveals the intergrowth of ZnO₂ and ZnO phases induced by stacking faults, with orientation relationship [101]ZnO₂//[010]_ZnO and (111)ZnO₂//(002)_ZnO.