Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; Processo FAPESP: 06/60013-5 ; Lanthanum modified lead zirconate titanate (PLZT) ceramics with a Zr/Ti (90/10) ratio were investigated for a 7 and 8 at% lanthanum content by dielectric spectroscopy, the Sawyer-Tower polarization technique and x-ray diffraction measurements. The ceramics were obtained using a standard ceramic method, showing an anti ferroelectric (orthorhombic) phase (Pbam). Electric field dependence of polarization (P-E) studies revealed slim-like hysteresis loop characteristics. The temperatures corresponding to the maximum real and imaginary parts of the dielectric permittivity were not only coincident, but also shown to be frequency independent. Results on dielectric response suggest a thermodynamic phase transition rather than a dipole glass/relaxor ferroelectric transition. on the other hand, the Curie temperature (T-C) was found to be negative. Using Landau's theory considerations, the obtained results have been interpreted in terms of an antiferroelectric-paraelectric (AFE-PE) phase transition. (C) 2009 Elsevier Ltd. All rights reserved.