Changes in dielectric response features of lead lanthanum zirconate titanate (PLZT) ceramics by manganese addition are reported in the present work. Both the PLZT relaxor behaviour and the frequency dependence of the room temperature dielectric constant are shown to be suppressed by the addition of manganese. Similar results are obtained by applying a bias external field or by chemical reduction of PLZT samples, thus indicating the presence of an interrelationship between oxygen vacancies and the random ‘bias’ electric field. Consequently, the defects created by oxygen vacancies appear as the most important factor causing the disappearance of relaxor behaviour in Mn-doped PLZT ceramics. No modifications in the diffuse phase transition with the manganese content are found, which may be due to the persistence of compositional disorder. Additionally, it was verified that the spin glass model cannot be used to describe these observed effects.

Temperature dielectric behavior in oxidized and non-oxidized PZT (60/40) and PZT (40/60) ceramics were analyzed in a frequency and temperature range of 1 kHz-10 MHz and from 15 to 400 K, respectively. The results revealed an anomalous dielectric behavior at temperatures closed to 250 K inoxidized and non-oxidized PZT samples. Temperature polarization behavior in pyro-electric measurementshows monotony changed in the same temperature range. Dipolar behavior could be the cause of detectedanomaly.Keywords: perovskite structure, temperature dielectric behavior, oxidation, reduction, PZT.

High-energy ball milling technique was successfully applied to calcinated lead zirconate titanate (PZT 60/40) powders. After 20 h of ball milling, large PZT particles were completely broken down, reducing its initial size in three orders of magnitude. Experimental results show a huge sinterability enhancement of the PZT powders by using this technique, achieving its maximum sintering rate at similar to 800 degrees C. Relatively low densities (similar to 91%) were achieved in stoichiometric samples, while in 3% lead excess samples sintered at 950 degrees C for 30, 45, 60, 90 and 120 min using a fast firing process and a post-annealing treatment at 800 degrees C for 4 h, densities of similar to 97% of the theoretical were achieved. PZT nanostructured ceramics prepared under optimized processing conditions (60 h of powder milling, 950 degrees C of sintering temperature, 60 min of sintering time and a post-annealing process at 800 degrees C during 4 h) show high dielectric constant (epsilon') values (900) and low dielectric loss (tan delta) at room temperature and a ferroelectric-paraelectric transition temperature at 375 degrees C.

Dielectric and direct piezoelectric responses in non-doped and Mn-doped Pb0.91La0.09(Zr0.65,Ti0.35)O3 ceramics are experimentally studied. The permittivity and the direct piezoelectric coefficient were measured by applying an ac electric field or a mechanical stress, respectively. The results show that the dielectric response is mainly due to an extrinsic contribution at room temperature. A notable reduction in room temperature dielectric losses by Mn-doping is verified. The temperature of the minimum of the losses depends on the Mn-content, enabling the Pb0.91La0.09(Zr0.65,Ti0.35)O3 properties to be tuned from soft to hard. A significant stabilization of the dielectric and piezoelectric responses, related to domain wall motion reduction, is confirmed in Mn-doped materials, so these materials become good candidates for transducer applications. The correlation between the dielectric constant and dielectric losses is discussed in terms of the Rayleigh model. Results show that Mn-doped PLZT response does not fit this model. This fact could be explained by taking into account the nature of the defects created by manganese addition. These complex defects act as pinning centers, and the reversible movement of domain walls provide a significant contribution to the response of these materials.

High-energy ball milling technique was successfully applied to a lead zirconate titanate_(PZT 60/40) powder to decrease its sintering temperature by 100 o C. The milling time was seen to have a marked effect on the refinement of the particles of PZT nanocrystalline powder. After ball milling for 20 h, the large particles were totally broken down and the grain size was reduced by three orders of magnitude. The results obtained are related to the rate of the injected energy and diffusion processes taken place.