Aluminum and Gallium Distribution in the Lu3(Al5-xGax)O12:Ce Multicomponent Garnet Scintillators Investigated by the Solid-State NMR and DFT calculations

TL;DR

This study combines solid-state NMR and DFT calculations to analyze how aluminum and gallium distribute over different sites in Lu3(Al5-xGax)O12 garnet crystals, revealing preferences influenced by ionic size.

Contribution

It provides new insights into the site preferences of Al and Ga in mixed garnets using combined experimental and theoretical approaches.

Findings

Ga prefers tetrahedral sites over octahedral ones.

Al and Ga distribution is non-uniform across sites.

Quadrupole coupling constants and chemical shifts were determined.

Abstract

Distribution of aluminum and gallium atoms over the tetrahedral and octahedral sites in the garnet structure was studied in the mixed Lu3Al5-xGaxO12 crystals using the 27Al and 71Ga MAS NMR together with the single crystal 71Ga NMR. The experimental study was accompanied by theoretical calculations based on the density functional theory in order to predict the tendency in substitutions of Al by Ga in the mixed garnets. Both experimental and theoretic results show a non-uniform distribution of Al and Ga over the tetrahedral and octahedral sites in the garnet structure, with strong preferences for Ga, having larger ionic radius than Al, to occupy the tetrahedral site with smaller volume in the garnet structure. The quadrupole coupling constants and chemical shift parameters for Al and Ga nuclei have been determined for all the studied compounds as well as electric field gradients at Al and Ga nuclei were calculated in the framework of the density functional theory.