Determination of the electric field gradient tensor by 2D NQR

Abstract

For a full specification of the Electric Field Gradient (EFG) tensor, five independent parameters are necessary: the asymmetry parameter (η), the largest component of the EFG ( eq), and three angles which determine the orientation of the EFG principal axis with respect to the crystallographic frame. The parameters eq and η can be determined independently by pure Nuclear Quadrupole Resonance (NQR) (for nuclear spin I = 1 and I > 3 2 ). However, to determine the orientation angles one needs to use other methods such as X-ray Crystallography, Nuclear Magnetic Resonance (NMR), NQR with external field, EPR, Mössbauer spectroscopy or Perturbed Angular Correlations (PAC). In this paper we propose a new 2D NQR method which permits the full determination of the EFG tensor in a monocrystalline sample. It can be used to determine the preferential orientation of small monocrystals in a polycrystalline sample. The angular precision of the method is ± 2.5°.