Hyperfine Interactions 136/137: 523–528, 2001. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 523 Concentration Dependence of the Electric Field Gradient in PbZr 1-x Ti x O 3 Ceramics M. OLZON-DIONYSIO 1 , S. D. SOUZA 1 , A. P. AYALA 2 , A. CARBONARI 3 and E. LONGO 4 1 Departamento de Física - UFSCar - São Carlos, SP, Brazil 2 Departamento de Física - UFC, Fortaleza, CE, Brazil 3 Institutode Pesquisas Energéticas e Nucleares - CNEN/SP, São Paulo, SP, Brazil 4 Departamento de Química - UFSCar - São Carlos, SP, Brazil Abstract. The concentration dependence of the electric field gradient (EFG) in PZT ceramics was studied by Time Differential Perturbed Angular Correlations (PAC) using the 181 Ta radioactive probe in samples with x = 0.3, 0.5 and 0.8 at room temperature. This phase presents two sites, probably related to defects close to probes, caused by oxygen and lead vacancies. We can also state that both the paraelectric and ferroelectric phases of these systems have two sites with different characteristics and that the high-frequency quadrupolar frequency site presents the highest fraction. The concen- tration dependence revealed by our results is discussed by comparing the latter with previous PAC studies. 1. Introduction Lead titanate zirconate or PZT (PbZr 1-x Ti x O 3 ) is one of the most intensively studied ferroelectric materials mainly due to its technological applications. In the course of time, PZT has been the subject of many experimental and theoretical research efforts. This system presents an interesting concentration–temperature (x –T ) phase diagram and its physical properties can be associated with the several structural modifications found in. The x –T phase diagram determined by Jaffe et al. [1] presents a variety of phase transitions among ferroelectric, antiferroelec- tric and paraelectric phases. Increasing the Ti composition progressively yields the following phases: an antiferroelectric orthorhombic (AO) phase for x  0.05, a fer- roelectric rhombohedral-low temperature (FR(LT)) phase for 0.05  x  0.37, an- other ferroelectric rhombohedral-high temperature (FR(HT)) phase for 0.37  x  0.47, and finally, a tetragonal ferroelectric (FT) phase for x larger than 47%. The high-temperature phase of this solid solution in all compositions is the paraelectric cubic (PC) perovskite structure. PZT type ceramics belong to the general class of ceramics classified as per- ovskites and have an ABX 3 composition in which A and B are metallic cations and X is the non-metallic anion. Their structure is cubic, with B located in the cube’s center, A in the 8 corners and X occupying the center of each of the cube’s faces.