Electron paramagnetic resonance investigation of paramagnetic point defects in ZnO and ZnO-supported ruthenium

Abstract

Paramagnetic point defects sensitive to the surrounding atmosphere were observed in ZnO powder. Changes in EPR lines following either thermal-vacuum treatment or contact with molecular O₂ led to definite conclusions regarding the nature of the ZnO point defects and the electron-transfer processes active at the ZnO/O₂ interface. Two different point defects are identified: A (g_A= 1.955), assigned to ionized interstitial zinc centres Zn⁺_i, and B (g_B= 1.958), assigned to ionized oxygen vacancies v⁺_o. Both are able to reduce molecular oxygen, but only v⁺_o defects give rise to O^–₂. ZnO-supported ruthenium was also investigated: dispersed Ru improves the electron transfer from the oxide to the O₂ molecules of the surrounding atmosphere.