GRAIN-GROWTH OF SINTERED ZNO WITH ALKALI OXIDE ADDITIONS

The grain growth of ZnO with Li2O and Na2O additions was studied and i s compared with a previous report of the effect of K2O. These three al kali oxides each decrease the rate of ZnO grain growth. Their effects on ZnO grain growth are quantitatively described in terms of the kinet ic grain growth equation: G(n) - G0n = K0.t.exp(-Q/RT). The parameters are compared with similar analyses of the grain growth of pure ZnO. A pparent activation energies, Q's, for ZnO grain growth with alkali oxi de additions increase in the order: Li2O, Na2O and K2O. Two ZnO grain growth inhibition mechanisms appear to be active, including: (1) alkal i oxide solute segregation to the ZnO grain boundaries creating a drag mechanism that reduces the grain boundary mobility, and (2) a reducti on of the cation vacancy concentration and the occupation of interstit ial sites by the alkali cations in solution in the ZnO wurtzite struct ure. This latter mechanism reduces the rate of diffusion of Zn2+ durin g grain growth.