SOL-GEL PROCESSING AND PROPERTIES OF LEAD MAGNESIUM NIOBATE POWDERS AND THIN-LAYERS

Lead magnesium niobate powders and thin layers were formed from an alkoxide-based solution by sol-gel methods. The solution was synthesized by reacting a magnesium-niobium alkoxide solution with a lead acetate-based precursor solution. The effects of gelation conditions on the properties of the dried gel, and on the organic decomposition behaviour and crystalline phase development in gel-derived powders are reported. Gels prepared with greater molar ratios of water to alkoxide (3:1) had the largest surface areas (130 m22 g-1) and required the lowest temperature (320 ° C) for organic removal. The perovskite phase first appeared at temperatures near 700 ° C, and developed at a faster rate in gels prepared with higher water contents. Approximately 95% developed after 1 h at 700 ° C, or 5 min at 775 ° C. Dielectric thin layers were prepared on platinum-coated silicon substrates by a multilayered spin-casting method. The perovskite phase formed most readily in the thin layers by a fast-firing treatment at 800 ° C. Microstructures and electrical properties are reported for the integrated thin layer dielectrics. Ferroelectric hysteresis loops were observed. © 1990 Chapman and Hall Ltd.