Electric field gradient in Mg and Zn detected by β-emitters,⁸Li and¹²x0392;x0392;x0392;

Abstract

The quadrupole coupling constants of⁸Li and¹²B in hcp Mg and Zn are determined by use of a newly developed nuclear quadrupole resonance technique (NNQR) as ¦eqQ(⁸Li in Mg)/h¦=3.0±0.3 kHz, ¦eqQ(⁸Li in Zn)/h¦=33.5±2 kHz, and ¦eqQ(¹²B in Mg)/h¦=47.0±0.1 kHz. Correspondingly, the electric field gradients at room temperature are deduced: ¦q(⁸Li in Mg)¦=(3.81±0.39)×10¹⁸, ¦q(⁸Li in Zn)¦=(4.25±0.27)×10¹⁹, and ¦q(¹²B in Mg)¦=(1.47±0.03)×10²⁰, all in V/m². The experiments are compared with the results of first-principles super-cell band structure calculations which can treat local lattice relaxations around the impurity nuclei. The calculations show that the most favorable location of these light interstitials in hcp Mg is not the octahedral-like sites which have the biggest interstitial volume, but the basal trigonal sites with a local lattice expansion of as big as 30%. Calculated electric field gradients at the impurity nuclei reproduce the experimental values fairly well.