Surface concentration of defects at grain boundaries in sintered alumina determined by positron annihilation lifetime spectroscopy

Abstract

Sintered alumina samples of grain diameters spanning from 1.2 to 4: 5 ñm have been investigated by positron annihilation lifetime spectroscopy. One series of samples was produced from material containing about 150 ppm impurities (mainly SiO 2 ). T he second one was made from material having about 2700 ppm of various elements (SiO 2 , MgO , CaO). Two models of positron trapping at grain boundari es are compared : The first one relates to the diffusion -limited regime ; and the other one - to the transition -limited regime of trapping. As a result the relative change of surface concentration of defects at grain boundarie s is determined. Additionally , the positron diffusion constant in bulk alumina at room temperature, D + = 0: 3 6 Ï 10 cm 2 /s, is estimated.