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The 93Nb NMR spectra of a mixed KTa1-x Nbx O3 (KTN) single crystal with x = 15% have been measured. The observation of an unresolved quadrupole-induced first-order satellite background below the sharp central ½ ↔ -½ transition already in the cubic phase demonstrates that the Nb ions occupy off-center positions rather than the high symmetry central perovskite site. The angular dependence of the second moments of the satellite background further shows that these distortions are of rhombohedral symmetry, i.e. the Nb ions are displaced along the [111] body diagonals. [ABSTRACT FROM AUTHOR]

The 93Nb NMR spectra of a mixed KTa1-x Nbx O3 (KTN) single crystal with x = 15% have been measured. The observation of an unresolved quadrupole-induced first-order satellite background below the sharp central ½ ↔ -½ transition already in the cubic phase demonstrates that the Nb ions occupy off-center positions rather than the high symmetry central perovskite site. The angular dependence of the second moments of the satellite background further shows that these distortions are of rhombohedral symmetry, i.e. the Nb ions are displaced along the [111] body diagonals. [ABSTRACT FROM AUTHOR]

A coupled spherical random bond--random field pseudospin phonon model is presented, which explains the effects of pressure on the relative stability of the ferroelectric, relaxor-, and paraelectric-like phases and thus the temperature-pressure phase diagram of relaxor systems. Within this model we derived an expression for the dynamic susceptibility of relaxors, which describes the pressure and temperature dependence of the peak in the dynamic dielectric permittivity. The NMR spectral line shapes of PMN as well agree with the proposed model. [ABSTRACT FROM AUTHOR]

A 2.8 kV/cm electric field has been applied parallel to the external magnetic field along the [111] direction of a PMN single crystal and the 207Pb NMR spectra were measured at 9.1 T. Whereas the zero field cooled (ZFC) spectrum exhibits a Gaussian-like line shape, the FC spectrum clearly shows a two peak structure. One of the two peaks coincides with the ZFC spectrum. The other peak is shifted by about 100 kHz towards lower frequencies with respect to the ZFC peak and seems to be characteristic for the ferroelectric state. The ferroelectric shift agrees with the predictions of the spherical random bond–random field model. [Copyright &y& Elsevier]