Barium-137 nuclear magnetic resonance study in the various phases of BaTiO3

Ba-137 quadrupole perturbed NMR measurements on a multidomain crystal were performed in order to determine the quadrupole tensors (which are proportio nal to the electric field gradient (EFG) tensors) in the tetragonal, orthor hombic and rhombohedral phase of BaTiO3. Because of the relatively large qu adrupole splitting, only the central transitions were analysed. By means of the well known Volkoff theory the principal values and the directions of t he principal axes were evaluated from the angular dependent NMR spectra. Fu rthermore, the correct determination of the principal values of the quadrup ole tensors has been controlled by means of measurements on polycrystalline BaTiO3 samples of the same origin. The conclusions from the measurements o n the multidomain crystals are in very good agreement with the results of B a-137 NMR line shape measurements on powdered samples. Moreover, the NMR st udies on the crystal sample allow a study of the domain structure in the di fferent ferroelectric phases in complete agreement with the predictions fro m symmetry considerations.