LOCAL PIEZOELECTRICITY IN SrTiO3-BiTiO3 CERAMICS

Local piezoelectric properties of Bi-doped SrTiO3 ceramics have been investigated by piezoresponse force microscopy. The appearance of both out-of-plane and in-plane polarization components confirmed the piezoelectric nature of the obtained signal. The absence of labyrinth-like structures in observed piezoelectric contrast is not consistent with the expected existence of a relaxor ferroelectric state in this material. The close similarity of local piezoelectric properties in Bi-doped SrTiO3 with pure SrTiO3 suggests that the origin of obtained piezoresponse can be attributed to the flexoelectric phenomenon. Bi-doping leads to occurrence of oxygen vacancies and negative charge on the surface of the sample

Cu NMR Study of Detwinned Single Crystals of Ortho--II YBCO6.5

Copper NMR has been used as a local probe of the oxygen ordering in Ortho--II YBa2Cu3O6.5 crystals grown in BaZrO3 crucibles. Line assignments have been made to each of the expected crystallographically inequivalent sites. The presence of distinct and narrow lines for these sites as well as the lack of a line known to be associated with oxygen defects indicates that these crystals are highly stoichiometric. Our estimate of the lower limit on the chain length is consistent with that derived from X-ray diffraction measurements. In addition, we have found no evidence for static magnetic moments, in contrast to some previous results.Comment: 11 pages, 7 figures, submitted to Physica

Two-photon parametric pumping versus two-photon absorption: A quantum jump approach

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ON ERGODIC RELAXATION TIME IN THE THREE-DIMENSIONAL ISING MODEL

We have studied the dynamical decay of the autocorrelation function of the 3D Ising model for different sizes L = 20-52 of spin cluster-cubes. The behaviour of the longest, ergodic relaxation time, τ e , of a finite domain below the phase transition temperature T c was mostly considered for two types of phase transition dynamics. A study of the scaling properties of τ e demonstrates a negligible difference between the types of dynamics used, but a considerable difference for different boundary conditions. In contrast to the known result for periodic boundary conditions (τ e ~ L z exp [const(L