Seeded Hydrothermal Growth of Large PZT Crystals and Single-Crystal Array Transducers

This SBIR Phase I project seeks to provide large seeds for the hydrothermal growth of centimeter-size lead zirconate titanate (PZT) crystals. Large crystals of strontium titanate (ST) and lanthanum alumminate (LA) share the same perovskite crystal structure with PZT and are readily available candidate for the heteroepitaxial growth of PZT. There is, however, a large a-axis lattice mismatch that inhibits nucleation of the PZT phase. Our preliminary experiments suggest that a sputtered nanolayer of PZT on ST substrated provides numerous nucleation sited for the hydrothermal growth of a dense single-crystal PZT overlayer ( as shown by our FESEM and X-ray diffraction studies). The nanostructured interlayer eases the transition between the substrate lattice and the PZT lattice, accommodating the lattice mismatch and relieving the accompanying stress. Having circumvented the lattice mismatch problem, hydrothermal processing should provide a high growth rate leading to a large single crystals of PZT in reasonably short time. In Phase I program we will test the feasibility of hydrothermally growing single crystals of PZT on interlayer prepared ST and LA seeds (5mm x 5mm). We will also examine the feasibility of growing single crystal arrays on substrates that have an interlayer pattern written upon them.