روزنامه با شماره پیاپی سال 2008

4

122

125

Electron paramagnetic-resonance measurements were carried out to study the structure of paramagnetic centres in ZnO+1% MnO2 powder mixtures, processed by a ball-milling technique during different treatment times, t MT . Initiation of five different types of paramagnetic centres, I–V, was revealed. The electron-hole centres I (V Zn−:Zni0), II (V Zn−), and III ((V Zn−)2−) in ZnO first appear and then disappear with the mechanical treatment (different times t MT for different centres). It indicates that the formation of vacancies and other defects in ZnO have various reaction energies and that on annealing at higher temperatures, T MT , the defects having smaller activation energies are not stable. The formation of intermediate IV type centre is associated with diffusion of Mn2+ ions into a superficial Zn(OH)2 environment. The subsequent formation of spectrum V associated with the solid solution ZnO:Mn2+, begins at t M T > 90 min .

Acta Tropica

2008

Acta Tropica