Positron annihilation studies on nasicon analogues containing cation vacancies

Abstract

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. Keywortk. Nasicon analogue; positron annihilation spectroscopy; cation vacancies; trapping rate.

Influence of Reduced Na Vacancy Concentrations in the Sodium Superionic Conductors Na11+xSn2P1–xMxS12 (M = Sn, Ge)

“…In addition, changes in the carrier density are most likely expected to change the defect formation enthalpy. While defect formation enthalpies are often disregarded in superionic conductors, as they are thought to be negligible compared to migration enthalpy, recent reports suggest non-negligible influences of sodium or sodium vacancy concentrations in the fast ionic conductors Na 3– x PS 4– x Cl x and Na 3– x M 1– x Zr x Cl 6 . ,, Assessing changes in defect structures is experimentally challenging, but should be investigated prospectively with positron annihilation (lifetime) spectroscopy, which has been carried out on sodium solid electrolytes before, and may lead to further insights into vacancy-influenced ionic transport in this class of materials.…”