The local structure of LiB_(3)O_(5) single crystal was investigated with ~(7)Li (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 η=0.6±0.1 for ~(7)Li. 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 ~(7)Li 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.
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