Local structure of LiB3O5 single crystal from Li-7 nuclear magnetic resonance

Abstract

The local structure of LiB3O5 single crystal was investigated with Li-7 (I=3/2) nuclear magnetic resonance measurements. We observed four different spectra, which could be divided into two groups corresponding to two kinds of lithium atoms, Li-A and Li-B, lying at crystallographically equivalent sites and magnetically inequivalent sites. From these results, the quadrupole coupling constants and the asymmetry parameters were determined at room temperature and are e(2)qQ/h=143+/-1 kHz and eta=0.6+/-0.1 for Li-7. The directions of the principal axes of the electric field gradient tensors were also determined. The spectra for the two groups have the same principal values of the electric field gradient tensor, but different orientations, and originate from magnetically inequivalent sites. Also, the Li-7 spin-lattice relaxation rate was measured, and the measured relaxation rate was found to be proportional to the temperature. The temperature-dependent single phonon process is considered to be more effective than the Raman process for nuclear quadrupole relaxation. In addition, we discuss the correlation between the asymmetry parameter and the largest nonlinear optical coefficient. (C) 2003 American Institute of Physics.