New Li+ ferroelectric conductors with tetragonal tungsten bronze structure

The evolution of conductivity in tetragonal tungsten bronze (TTB) oxides be longing to the Pb5(1-x)Li10xTa10O30 solid solution was studied using two te chniques: a.c. complex impedance spectroscopy and the four-probe method. Th e results obtained from both techniques allowed the correlation of the evol ution of conductivity with composition. Indeed, the conductivity mainly app ears to be governed by the total number of Li+ ions in the structure. Furth ermore, it seems that when the number of Li+ ions in the structure is small , two separated regions appear: a low temperature region (LT), characterized by activation energy Delta E-L T, a very small number of mobile ions and a low value of the prefactor sigm a(0); a high temperature region (HT), characterized by activation energy Delta E- HT (Delta E-HT > Delta E-LT), a larger number of charge carriers and a high er value of the prefactor sigma(0). The existence of these two regions is explained in terms of extrinsic-intri nsic behavior. Dielectric measurements were also performed, with the substi tution 2Li(+)-Pb2+ leading to a decrease of the Curie temperature which is explained in terms of chemical bonding and antagonist effects. (C) 2000 Els evier Science B.V. All rights reserved.