SBIR-STTR Award

Single crystals of lead magnesium niobate-lead titanate have superior dielectric and piezoelectric properties. To date all crystals have been grown by flux techniques and sizes have been small. Also growth rates in flux systems are slow. In this study we will investigate growth of PMN-PT by a melt technique, specifically the Bridgman technique. We will study by DTA the liquidus and solidus temperature as a function of composition and from this data construct a preliminary phase diagram. Materials for and designs of crucibles will be evaluated to reduce or eliminate sticking of the grown crystal to the crucible. A two zone furnace will be used for Bridgman growth so that we will have more control over the temperature gradient at the melt-solid interface than would be possible with a single zone furnace. Using seeds cut from single crystals of PMN-PT we grow by the high temperature solution technique, seeded growth will be studied. Physical properties of crystals grown by the Bridgman technique will be measured for comparison with single crystals grown by other methods.

Single crystals of lead magnesium niobate-lead titanate solid solutions have been shown to have superior dielectric and piezoelectric properties. Initially growth of these crystals was accomplished by spontaneous nucleation and slow cooling. Crystals grown by this technique were small and inconsistant. More recently growth by the seeded high temperature solution growth technique has been shown to have promise. Phase I of Contract#: N00014-97-C-0439 provided an initial study of Bridgman growth of PMN-PT crystals. This study showed that compositionally uniform single crystals of PMN-PT could be grown by the Bridgeman method. Additionally it was shown that PMN-PT was compatible with platinum crucibles and that the vapor pressure at the melting point is low enough to be contained by sealed crucibles. This combination of properties makes Bridgman growth of PMN-PT viable. The work proposed within aims to bring this growth process to a manufacturing level. The study will start with seeded growth of one inch diameter boules. The perfection of the crystals will be determined as a function of crystallographic direction. Next the typical growth parameters such as thermal gradient at the melt-solidninterface, growth rate and cricible rotation rate will be optimized for growth of one inch diameter crystals. During the last part of the contract the conditions that gave the best growth will be used as a starting point for scale up to two inch diameter growth.