Nuclear quadrupole interactions of the Rb-87 nuclear magnetic resonance in a nonlinear optical crystal RbTiOAsO4

Abstract

The Rb-87 nuclear magnetic resonance (NMR) in a RbTiOAsO4 single crystal was investigated by employing a Bruker FT NMR spectrometer. Instead of one central line, four central lines were obtained. There were two sets of crystallographically inequivalent Rb+ ions: Rb(1) and Rb(2). Two resonance lines in the Rb(1) nucleus and two resonance lines in the Rb(2) nucleus were caused by magnetically inequivalent sites. The angular dependences led to different values for the quadrupole coupling constant and the asymmetry parameter: e(2)qQ/h = 19.26 +/- 0.03 MHz and eta = 0.59 +/- 0.02 for the Rb(1) ion, and e(2)q Q / h = 23.58 +/- 0.07 MHz and eta = 0.44 +/- 0.05 for the Rb(2) ion. The EFG tensors of Rb(1) and Rb(2) were non-axially symmetric, and the orientations of their principal axes did not coincide. The Rb(1) ions, which are surrounded by nine oxygen atoms, are low in symmetry while the Rb(2) ions, which are surrounded by nine oxygen atoms, show high symmetry.