Single-step deposition of gel-derived lead zirconate titanate films: Critical thickness and gel film to ceramic film conversion

PZT thin films were prepared on silica-glass substrates from Pb(CH3COO)(2).3H(2)O-Zr(n-OC3H7)(4)-Ti(i-OC3H7)(4)-H2O- CH3COOH-CH3OC2H4OH-n-C3H7OH solutions containing polyvinylpyrrolidone (PVP) via nonrepetitive dip-coating or spin-coating. The thickness of the gel films was varied by changing the substrate withdrawal and rotation speeds, and the crack formation was examined after firing the gel films at 700degreesC. The critical thickness, i.e., the maximum thickness achievable without crack formation, was maximized at a PZT/alkoxide mole ratio of similar to1, where crack-free PZT films as thick as 2 mum could be obtained via single-step deposition. Thermal analysis was conducted on gel films deposited on a glass substrate at similar to25degreesC and then peeled off the substrate. Infrared absorption spectroscopy and X-ray diffractometry measurements were conducted on films deposited on silicon wafers. These analyses revealed that PVP and CH3COO- were thermally decomposed at 250degrees-320degreesC, leaving carbonaceous species, followed by the crystallization of Pb-3(CO3)(2)(OH)(2) at similar to350degreesC. The oxidation of the carbonaceous; species occurred at similar to360degrees-460degreesC; perovskite PZT then was formed at similar to550degreesC. The film thickness decreased greatly at 200degrees-350degreesC, where thermal decomposition of PVP and CH3COO- occurred. The films fired at 700degreesC were rather porous and not very transparent. Preheating the gel films at 100degrees or 200degreesC resulted in particulate microstructure with gaps between the particles, and, at 350degreesC, caused crack formation, both of which further decreased the optical transmittance.