OXYGEN DISPLACEMENT THROUGH THE FERROELECTRIC PHASE-TRANSITION OF BARIUM-TITANATE - HIGH-TEMPERATURE O-17 NMR

Perovskite-structured BaTiO3 undergoes a ferroelectric tetragonal-to-c ubic phase transition at 130 degrees C. High-temperature O-17 MAS and static NMR line shapes and relaxation times were examined to elucidate the nature of the anion motions associated with the transition. O-17 MAS spectra show a gradual shift of the two oxygen peaks toward one an other with increasing temperature, and a sudden collapse to one peak a t the transition, which is consistent with its first-order character. O-17 T-1 data are relatively imprecise below the transition, but appea r to decrease above it, indicating an increase in low-frequency motion s, suggesting a dynamically averaged high-temperature phase.