27Al nuclear magnetic resonance of glassy and crystalline Zr(1-x)AlxO(2-x/2) materials prepared from solution precursors

Abstract

The local environment of the aluminum atoms in a series of metastable Zr(1-x)AlxO(2-x/2) crystalline materials (0.08 ≤ x ≤ 0.57), prepared by diffusion-limited crystallization of amorphous precursors, has been determined by 27Al magic angle spinning nuclear magnetic resonance (MAS NMR). Results show the existence of aluminum in 4-, 5-, and 6-fold coordination in both the amorphous and crystalline states. Although the relative amounts of each type of coordination show no compositional dependence in the amorphous state, the results for the crystalline materials show a systematic decrease in the average aluminum coordination number with increasing aluminum content. Comparisons of MAS NMR results between pure Al2O3 precursors and Zr(1-x)AlxO(2-x/2) crystalline materials processed under similar conditions show a profound effect of ZrO2 on the coordination environment of the aluminum atom. Both a random distribution model and a model that assumes small-scale clustering of aluminum ions are considered to explain the trends in the type of aluminum coordination as a function of composition.