Low temperature synthesis of ultrafine Pb(Zr, Ti)O 3 powder by sol-gel combustion
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Low temperature synthesis of ultrafine Pb(Zr, Ti)O3 powder by sol-gel combustion J. Sch¨afer, W. Sigmund, S. Roy, and F. Aldinger Max-Planck-Institut f¨ur Metallforschung, Pulvermetallurgisches Laboratorium und Institut f¨ur Nichtmetallische Anorganische Materialien, Universit¨at Stuttgart, Heisenbergstrasse 5, 70569 Stuttgart, Germany (Received 11 November 1996; accepted 17 February 1997)
Lead zirconate titanate powders are derived from a novel aqueous-based citrate-nitrate/oxynitrate sol-gel combustion process. Aqueous solutions of metal nitrates or oxynitrates are transformed into gels with citric acid under heating. The received gels undergo a self-propagating combustion reaction on heating to 180 ±C and subsequently yield voluminous ashes. These ashes form single phase perovskite Pb(Zr0.53 Ti0.47 )O3 powder with a specific surface area of 8 m2yg upon calcination at 550 ±C. The ashes show a homogeneous distribution of lead, zirconium, and titanium ions which guarantees short diffusion paths in solid state formation of PZT perovskite. The redox behavior of the gels was studied with the help of DTA experiments. Powders are characterized in terms of XRD, SEM, and EDX analysis.
Solid solutions of PZT contribute in a wide range of ZryTi stoichiometry to a group of electroceramic materials with exceptional piezoelectric-ferroelectric, dielectric, and electro-optic properties.1 The quality of the sintered PZT specimen strongly depends on the chemical homogeneity, particle size, and morphology of the starting powder. Thus processing routes2 for the synthesis of PZT powders always play a major role for the properties of the sintered material. Various synthetic routes like the conventional mixedoxide process,3,4 the hydrothermal route,5,6 sol-gel route,7–9 and other chemical processes2,10,11 are studied in order to prepare a more homogeneous PZT powder. PZT with ZryTi ratios near the morphotropic phase boundary (MPB) respectively Pb(Zr0.53 Ti0.47 )O3 has the highest dielectric constant and is therefore a preferred capacitor material. The “width” of the MPB’s two-phase region,12–15 where ferroelectric rhombohedral and ferroelectric tetragonal phases coexist, depends according to some authors5 on the atomistic distribution of Zr and Ti ions. In this work, we focus on the synthesis of PZT powders by a sol-gel combustion technique— a novel way and unique combination of the combustion process and the chemical gelation process. The process exploits the advantages of inexpensive precursors, a simple preparation method, and a resulting ultrafine, homogeneous, highly reactive powder. The synthesis has been studied in different ceramic systems as published elsewhere.16,17 Pb(Zr0.53 Ti0.47 )O3 as composition near the MPB of the PZT system was chosen for the present investigation. It is also understood that the width of the MPB’s two-phase region is very narrow and strongly depends on the extent of Zr and Ti ion distribution in the composition.5 2518
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