Determination of the electric field gradient tensor by 2D NQR

For a full specification of the Electric Field Gradient (EFG) tensor, five independent parameters are necessary: the asymmetry parameter (eta), the largest component of the EFG leg), and three angles which determine the orientation of the EFG principal axis with respect to the crystallographic frame. The parameters eq and eta 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, Mossbauer 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 degrees. (C) 1997 Elsevier Science Ltd.