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

For the low-temperature phase beta-BaB2O4 single crystal, the rotation patt erns of the nuclear magnetic resonance spectra of the B-11 nucleus were mea sured in the three mutually perpendicular crystal planes. We observed twelv e sets of different spectra which can be divided into two groups. The six s ets in each group have the same principal values of the electric field grad ient tensor and originate from the chemically equivalent but magnetically i nequivalent sites. The nuclear quadrupole coupling constant (e(2)qQ/h) sind the asymmetry parameter (eta) at room temperature were determined in this study for the first time, and are as follows: for B(1), e(2)qQ/h = 2.455 +/ - 0.006 MHz and eta = 0.684 +/- 0.015; and for B(2), e(2)qQ/h = 2.486 +/- 0 .006 MHz and eta = 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 rang e 140-420 K.