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suggesting that the rate determining step was viscous

flow.

The n value was influenced by the particle size, the

agglomeration shape and impurities type and content.

The Consideration of all this results suggests that per-

haps a grain growth mechanism occurs at critical impuri-

ties content and the mixing of dopants modified very

much the sintering kinetics.

4. Conclusions

From the point of view of the sintering, the same dopant

concentrations in A and B, the results for rel

, *

and

are similar. For the combination A + B, the sintered

state was not obtained. Both dopants inhibit the grain

growth and accelerate the sintering process. This effect

increases with the dopant concentration and with the

combination of both dopants. The phenomenological

model for viscous sintering suggests, in all the cases, that

sintering is governed by a reactive liquid process. The

phenomenological model for solid state sintering sug-

gests for PLZT and PZTN that the sintering rate deter-

mining step was coalescence and for PLZTN the rate

determining step was viscous flow. As the actual grains

are not identical in size and shape, the theoretical results

differs form the experimental ones to the Skorohod-

Olevsky Model.

5. Acknowledgments

The authors gratefu lly acknowledge the support from the

project PNCB 10/04, Cuba, and Prof. Dr. Jose Antonio

Eiras, Head of Department of Physics, Science and

Technology Center, UFSCar, Brazil, for providing SEM

facilities.

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