ELECTRIC-FIELD EFFECT ON NQR IN FERROELECTRIC MATERIALS

The electric field effect on NQR in ferroelectric materials, Nb-93 in LiNbO3 and N-14 in NaNO2 and SC(NH2)(2), has been investigated at 77 K . In these crystals with single domain, only the line shift due to the external electric field was observed. In the case of NaNO2 powder and a crystal with multidomains, line broadening was observed in the exte rnal electric field. These phenomena can be explained with the fact th at the direction of spontaneous polarization in a domain is related to the direction of the applied electric field. The rate of the NQR line -shift due to the electric held is remarkably smaller in mostly ionic crystals, such as LiNbO3 and NaNO2, than in a molecular crystal such a s SC(NH2)(2). This is due to the strong ionic bonding in ionic crystal s. Also, the difference of the Stark shift between NaNO2 and SC(NH2)(2 ) is discussed in terms of the local electric field and polarizability at the resonant nuclear site.