Local structure analysis of smoky and colorless topaz using single crystal Al-27 NMR

摘要

The angular dependence of the Al-27 NMR spectrum was measured for single crystals of smoky and colorless topaz, Al2SiO4(FOH)(2). Smoky topaz was obtained by irradiating high energy neutrons to colorless topaz. The quadrupole coupling constant e(2)Qq/h and the asymmetry parameter 17 were obtained from the analysis of the angular dependences of quadrupole splitting of the Al-27 NMR spectrum. The local structures around the aluminum atoms in smoky and colorless topaz were discussed from the magnitude and the direction of the electric field gradient. The directions of principal axes of the EFG tensor of Al-27 were close to the directions of Al-O and Al-F bonds. The difference in the bond lengths between Al(1)-F(1) and Al(1)-F(2) was found to affect the x and y components of the EFG tensor. (c) 2005 Elsevier Ltd. All rights reserved.