Multiple magnetic field Al-27 solid-state NMR study of the calcium aluminates CaAl4O7 and CaAl12O19

Al-27 NMR spectra are reported for the crystalline aluminates CaAl4O7 and C aAL2019 at three magnetic fields (8.45, 11.7, 14.1 T) using conventional an d 3Q fast magic angle spinning (MAS) NMR techniques. For CaAl4O7 two distin ct aluminate tetrahedra are observed, both of which are in triclusters and can be assigned on the basis of the structural distortion index. The NMR in teraction parameters deduced for these units allow useful comparison with o ther tetrahedra in triclusters. The spectra from CaAl12O19 can be simulated using five distinct signals (3 x AlO6, 1 x AlO5, Ix AlO4) which are assign ed to specific sites within the structure. Comparison is made with previous NMR studies of CaAl12O19 and with the structurally closely related phase S TAl12O19 Copyright (C) 2001 John Wiley & Sons, Ltd.