Nuclear quadrupole interactions of ¹¹B in -BaB₂O₄ single crystal studied by nuclear magnetic resonance

For the low-temperature phase -BaB₂O₄ single crystal, the rotation patterns of the nuclear magnetic resonance spectra of the ¹¹B nucleus were measured in the three mutually perpendicular crystal planes. We observed twelve sets of different spectra which can be divided into two groups. The six sets in each group have the same principal values of the electric field gradient tensor and originate from the chemically equivalent but magnetically inequivalent sites. The nuclear quadrupole coupling constant (e²qQ/h) and the asymmetry parameter () at room temperature were determined in this study for the first time, and are as follows: for B(1), e²qQ/h = 2.455±0.006 MHz and = 0.684±0.015; and for B(2), e²qQ/h = 2.486±0.006 MHz and = 0.644±0.019. The principal-axis orientations of the electric field gradient tensors were also determined. By investigating the temperature dependence of the quadrupole splittings, we find that the basic structural unit of the crystal hardly changes with temperature in the range 140-420 K.