Gradient-Elastic Tensor in Sodium Chloride and Sodium Bromide

Abstract

The effects of static elastic strain on the Nuclear Magnetic Resonance (NMR) spectra of NaCl and NaBr were used to determine the gradient elastic tensors for the ions in these crystals. The measured tensor components were compared with the results of a point-ion model to provide effective antishielding factors for the ions observed. The effective antishielding factors were found to be larger in the case of ${\mathrm{Na}}^{23}$ and smaller for ${\mathrm{Cl}}^{35}$ and ${\mathrm{Br}}^{79}$ than the corresponding theoretical antishielding factors. These discrepancies are explained by a consideration of first and second nearest-neighbor overlap effects.