Precipitate splitting in Pb 0.91 La 0.09 Zr 0.65 Ti 0.35 O 3 films
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Cengiz Ozkan University of California Riverside, Department of Mechanical Engineering, Riverside, California 92521
Ali Ata Department of Materials Science, Gebze Institute of Technology, Gebze 41400, Kocaeli, Turkey (Received 22 January 2001; accepted 23 July 2001)
The transformation to perovskite phase of Pb0.91La0.09Zr0.65Ti0.35O3 (9/65/35) films on r-sapphire and resulting annealed microstructures were examined by transmission electron microscopy. A random equiaxed polycrystalline grain morphology (approximately 600 nm) was observed after rapid-thermal annealing or furnace annealing when the as-deposited (radio-frequency-magnetron sputtering) films were predominantly pyrochlore. However, an interesting paired-plate structure was revealed after furnace annealing when the as-deposited films were fully perovskite. The average size of such a split precipitate was 35 nm in width and 150 nm in length. Phase transformations in the solid state have been known to often generate coherent second-phase precipitate particles. Particle shape transitions occur with a coherent precipitate increasing its size during either coarsening or growth stages. Sphere-to-cube and cubeto-cuboid or ellipsoid shape transitions are common. Precipitates are spherical when they are small initially and they become cuboidal as their size increases. In exception to this trend, some cuboid particles were observed to evolve into plate-shaped particles that split or fission into two (or more) smaller particles. This different type of transition, splitting of cuboid into two parallel platelike smaller particles, is termed precipitate splitting. Precipitate pair formation or precipitate splitting has been reported in Ni-based superalloys.1–3 The splitting and coarsening processes in such alloys have received a great deal of attention from researchers due to the formation and evolution of a variety of complex morphologies of precipitate particles in a parent matrix because of their impact on material properties. Theoretical analyses generally agree that particle splitting is related to the existence of internal stress in two-phase systems with significant lattice mismatch and low interfacial energy density. The balance between the interfacial energy and the elastic energy is an important determination of the morphology and splitting.
a)
Present address: Kulicke and Soffa Test Products, 1150 N. Fiesta Blvd., Gilbert, Arizona 85233. b) Present address: Conexant Systems, 4311 Jamboree Rd., H01109, Newport Beach, California 92660. J. Mater. Res., Vol. 16, No. 10, Oct 2001
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Pb0.91La0.09Zr0.65Ti0.35O3 (PLZT) films are of interest for applications in pyroelectric, memory, and electrooptic devices integrated with semiconductors and the microstructure of the film directly influences the properties and thus the device performance. We reported the microstructures by scanning electron microscopy (SEM) featuring precipitate pairs in ferroelectric PLZT thin films for the first time.4 Phase transformation kin
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