Investigation of dielectric anomalies at cryogenic temperatures in the   (1-x)[Pb(Mg1/3 Nb2/3)O3]-xPbTiO3 system
  Complex electrical permittivity measurements in (1-x)[Pb(Mg1/3 Nb2/3)O3]-xPbTiO3 ceramics for 0.10 x 0.40 were performed in the frequency and temperature range from 1 kHz to 100 kHz and from 15 to 600 K, respectively. Unexpected dielectric anomalies, which were frequency dependent, were found at cryogenic temperatures. It was verified that this dielectric behavior is always observed, independently of whether the composition presents a "normal" ferroelectric or a relaxor characteristic. The results were analyzed within the framework of two current models found in the literature. It was concluded that none of the proposed mechanisms uniquely satisfies the experimental results in the composition range investigated here. 
M. H. Lente, A. L. Zanin, E. R. M. Andreeta, I. A. Santos, D. Garcia   and J. A. Eiras