John S. Wright

Phase development in Si modified sol-gel-derived lead titanate

Sol-gel methods were used to prepare chemically modified lead titanate (PT) powders. A PT alkoxide solution was synthesized and doped with Si (2–12 mole%) or with equimolar amounts (2–12 mole%) of Si and Pb through the addition of Si and Pb–Si alkoxide solutions, respectively. PT alkoxide solutions were also prepared with excess Pb and Ti (7 and 10 mole%). Gels were prepared through controlled additions of water. Crystalline phase development of gel-derived powders with heat treatment (400–700 °C) was studied using x-ray diffraction (XRD) and differential thermal analysis (DTA). While PT powders without added Si crystallized directly into a perovskite phase, Si modified materials crystallized first into a pyrochlore phase and at a higher temperature transformed into perovskite. The pyrochlore lattice parameter and the temperature for the transformation to perovskite increased with Si content. In all cases, the crystal structure of the final perovskite phase was not affected by the Si addition. The effect of Si on phase development and mechanisms of transformation is discussed.

Processing and Piezoelectric Properties of Mod Pzt Films and Pzt/Polymer Composite Coatings

Lead zirconate titanate, Pb(Zr 0.53 Ti 0.47 )O 3 (PZT), coatings were prepared using a metallorganic decomposition (MOD) route with lead and titanium acetates and zirconium acetylacetonate in acetic acid and water. Films with thickness of 0.66 μm were prepared on (100) Si with a layered bottom electrode (Pt/Ti/TiO 2 /SiO 2 ). Dielectric constant and loss were 1100 and 0.04 (1 kHz), respectively, and remnant polarization and coercive field were 30 μC/cm 2 and 40 kV/cm. Piezoelectric coefficient (d 33 ) of the PZT film, measured with a singlebeam laser interferometer, was 41 pm/V. Standard micromachining techniques were used to etch the PZT to form discrete PZT posts for preparation of the ceramic phase for composite coatings with a 1–3 connectivity. SEM was used to determine the dense and etched film microstructure. Preliminary ion milling results, used to etch the PZT, are also presented.

Effect of solution processing on PZT thin films prepared by a hybrid MOD solution deposition route

Lead zirconate titanate, Pb(Zr0.53Ti0.47)O3 (PZT), thin films were prepared by a hybrid metalorganic decomposition (MOD) solution deposition route; the effects of processing conditions on the film structure and properties were investigated. Solutions were synthesized by mixing and reacting Zr acetylacetonate and Pb acetate trihydrate with a solution prepared from Ti isopropoxide, acetic acid and water. Chemical changes in the solution during preparation and solution storage (i.e., aging) were investigated by visual observation and FTIR, and were evidenced by changes in phase content and properties of the final PZT films. Results suggest that Zr acetylacetonate and Pb acetate trihydrate react with a Ti oxoacetate-based precursor, and that this reaction continues during aging at room temperature. The PZT film quality and properties improved with aging time of the solution before deposition. To achieve good properties and design a convenient processing route, an accelerated aging scheme, including a brief aging at 60°C and freezing to prevent further reaction, was developed. PZT films prepared from these solutions had average dielectric constants of ∼1040, loss tangents of ∼0.05, remnant polarizations of ∼26 μC/cm2, and coercive fields of ∼39 kV/cm.

Characterization of sol-gel derived (Pb,Ba)(Zr,Ti,Nb)O3 thin films for optical waveguide development

(PbBa)(ZrTiNb)0 3 thin films and powders have been prepared using the sol-gel technique. Solutions were synthesized in 2-methoxyethanol based upon our previous PZT solution preparation. Three different approaches were used for incorporating barium into PZT alkoxide solutions. Thermal analysis and x-ray diffraction results indicated that barium methoxypropoxide gave the best results. PBZTN (71% Pb and 71% Zr) was deposited onto sapphire substrates as well as oxidized silicon substrates. Optical transmission measurements showed greater than 80% transmission for wavelengths longer than 400 nm. Films with thickness of 3000 A on sapphire exhibited a refractive index of 2.19 at λ=633 nm.

Sol-gel processing and structure development of lead titanate particles

Spherical particles of lead titanate, PbTiO{sub 3}, (PT) were prepared from partially hydrolyzed alkoxide solutions modified with benzoic acid. Modified and aged alkoxide solutions were added dropwise to isopropyl alcohol, forming particles (0.2 to 1.0 {mu}m in diameter). FTIR spectroscopy results demonstrate chelation of the PT alkoxide which prevented the formation of an extended gel network. Diffuse reflectance FTIR (DRIFT) spectra indicate the benzoate ligands are present until 450 C; TGA results show significant weight loss at 450 C. PT particles crystallize into the perovskite phase at {approx}450 C, as determined by DTA and XRD. The relatively low crystallization temperature may be due to the effect of benzoate ligands on amorphous structure and presence of internal surfaces.