137Ba and 47,49Ti NMR: electric field gradients in the non-cubic phases of BaTiO3

Electric field gradients have been measured at the Ba, and Ti sites in BaTiO3 from 137Ba and 47,49Ti NMR spectra of a recrystallized, strain-free polycrystalline specimen in the ferroelectric tetragonal, orthorhombic and rhombohedral phases. The strain-free nature of the recrystallized material has been established with convergent beam electron diffraction patterns and electron micrographs. The electric field gradients at the Ba and Ti sites in the rhombohedral phase are compared with recent theoretical predictions.