No abstract

No abstract

KTa& Nb 03 (KTN) in an intermediate-concentration range (x= 15.7%) has been studied using dielectric-constant and spontaneous-polarization measurements. A large peak in the dielectric constant (e,"=70000)is observed at the temperature T, *. From room temperature down to T, *+20 K, e obeys a Curie-gneiss law with To-142.3 K. Below, e deviates from this law and P-E hysteresis loops are observed. These results indicate that the phase transition exhibits a diffuse character which is related to the appearance of microscopic polarized regions or cells. The e peak at T, * exhibits a cusp shape and becomes Battened upon application of low dc-bias fields. A corresponding dielectric loss peak is also observed, the position of which reveals the relaxational character of the transition. Through measurements of e(E, T) for different dc-bias fields, we have characterized the dielectric nonlinearities in the transition range; the first nonlinear coefficient, e(', diverges in two distinct ranges, as (T-T,) ", with n-9 initially and with n = 2 closer to T, *. These results suggest that diffuse phase transitions in mixed ferroelectrics are due to the ordering of polar cells modified by mutual strain interactions.

Dielectric and elastic constant measurements have been performed on a KTN crystal with 15.7% Nb crystal at various DC bias electric fields. The temperature and field dependences of the two constants are shown t c b e related to the presence of polarization fluctuations. Near the transition, both constants exhibit non-linearities that have been experimentally characterized.

No abstract