Combined 135/137Ba Solid-State NMR at an Ultrahigh Magnetic Field and Computational Study of β-Barium Borate

beta-Barium Borate beta-BBO or beta-BaB2O4) is all important nonlinear optical material with many practical applications. In this work, we have directly probed the local Ba environment in beta-BBO by acquiring static Ba-135 and Ba-137 solid-state NMR spectra at all ultrahigh magnetic field of 21.1 T The observed spectra ire completely dominated by the second-order quadrupolar interaction. The measured quadrupolar coupling constants ire 14.9 and 22.8 MHz for Ba-135 and Ba-137, respectively A computational study of the electric field gradient tensor at Ba2+ was also performed using both plane-wave pseudopotentials (CASTEP) and ab initio (Gaussian 03) methods. Combining the experimental and theoretical results allows One to shed some light on the controversy regarding the true space group of beta-BBO. We conclude that the space group R3c represents the true structure of beta-BBO rather than does the space group R3. This work demonstrates that a combination of Ba-135/137 NMR and theoretical calculations is a useful tool for characterization of Ba-containing materials with unknown or poorly described Structures.