| Popis: |
47,49 Ti and 137 Ba NMR measurements were performed on single-domain pure BaTiO 3 crystals between room temperature and 1700 K. In the tetragonal phase ( T T c ≈ 400 K), the NMR lines show a temperature dependent quadrupole shift Δν Q associated with the electrical polarization P s . Relating P s with Δν Q , the underlying electric field gradient is found to be proportional to the square of the order parameter. The temperature variation of Δν Q is shown to fit Landau's relation of first-order phase transitions. The observed nuclear spin relaxation rates consist of three contributions: A classical phonon contribution, a diffusion-induced contribution above T c due to the motion of oxygen vacancies, and a contribution in the vicinity of T c related to the phase transition. From the latter, the correlation time associated with the dynamics of the phase transition was determined. |
