Lead magnesium niobate (PMN) and its solid solution with lead titanate (PMN-PT) are known for many technologically important applications such as high dielectrics, actuators, transducers, electro-opics, etc. Because of their potential use as ferroelectric relaxors and capacitors, there is a need to produce homogenous powders that are phase pure with the perovskite structure. It is important that the appearance of the pyrochlore structure be avoided. This phase often appears as an impurity that is known to significantly degrade the dielectric constant and other physical properties of dense PMN-PT ceramics. The pyrochlore phase is also a hindrance to solid state conversion processes leading to the growth of large PMN-PT single crystals.Besides other limitations, most of the synthesis methodologies devised up to now have not overcome the problem of pyrochlore formation. These methods include the columbite process, the sol-gel process and co-precipitation process. The columbite process is most widely employed, but requires excess lead and magnesium oxides for efficient fabrication but cannot be tolerated for most applications. The sol-gel process is thought to be the best but is costly, complicated and a difficult process for handling. It also relies heavily on the used of metal organic compounds which sometimes lead to the incorporation of carbon - a sometimes problematic impurity. Co-precipitation is more economical and simple but is fraught with issues of irreproducibility. Generally, all of these current processes have yet to be improved to the point that they yield highly phase-pure PMN and PMN-PT. Researchers at Arizona State University have developed a low cost method for producing highly reactive and well sinterable powders of lead magnesium niobate and its solid solution with lead titanate. These powders are converted to the perovskite structure and are completely free of the pyrochlore phase that typically appears impurity in other processes. They are expected to be important in the production of dielectric ceramics for capacitor and ferroelectric applications. Moreover, they are likely to be an appropriate precursor for the solid state, crystal growth conversion of powders directly into single crystals for ferroelectric relaxor applications.
|Published - Jul 12 1999