Positron-annihilation studies on nasicon analogs containing cation vacancies

Positron annihilation studies were carried out on the Nasicon analogue Na2(La, AI)Zr(PO4)3 compound for three different concentrations (2-2, 2"8 and 5.2 by wt.%) of ZrO 2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2.8 (wt.%) of ZrO 2. Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a twostate trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies