A study of inter-crystallite spaces in some polycrystalline inorganic systems using positron annihilation lifetime spectroscopy

Abstract

Positron annihilation lifetime spectroscopy (PALS) was used for calculation of number density and effective sizes of free volume holes (inter-crystallite spaces) in polycrystal CaSO4, CaCO3 (vaterit) and Ca10(PO4)6(OH)2 (apatite). The effect of substitution of two-valence Ca(II) for three-valence Eu(III) on annihilation characteristics of apatite, studied together with the data on thermo-stimulated luminescence (TSL) and low-temperature sorption of gas (N2), helped to elucidate mechanism of positronium atom (Ps) localization in the free volume holes and perform corresponding calculations. It came out that PALS is more sensitive to inter-crystallite sites (1016 cm-3) in polycrystallites than to the free volume holes in polymer glasses (1019 cm-3). This is due to higher mobility of the precursor of localized Ps in crystallites. © 2006 Elsevier Ltd. All rights reserved.