Lead Zirconate Titanate Via Reaction Sintering of Hydroxide Precursors
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Lead zirconate titanate via reaction sintering of hydroxide precursors Xue Junmin and John Wanga) Department of Materials Science, Faculty of Science, National University of Singapore, 119260 Singapore (Received 26 July 1998; accepted 14 September 1998)
Lead zirconate titanate (PZT) has been successfully fabricated via a unique one-step sintering processing route, which is simpler than the traditional precursor-calcinationmilling-pelleting-sintering route and is able to deliver an enhanced sintered density at a much reduced sintering temperature. The hydroxide precursor was prepared by coprecipitation from a mixed nitrate solution containing Pb21 , Zr41 , and Ti41 ions, and it was then compacted into pellets without being calcined at a low temperature. The precursor pellets were dehydrated at 400, 500, and 600 ±C for 4 h, respectively, followed by an isostatic pressing at 350 MPa, prior to being sintered at a high temperature. Dehydration temperature has a large impact on the sintering behavior of these hydroxide-derived PZT ceramics. The PZT dehydrated at 400 ±C was seriously cracked when sintered at temperatures ranging from 950 to 1150 ±C, due to the incomplete dehydration. A sintered density of 99.2% theoretical density was obtained at 1050 ±C for 2 h for the powder pellet dehydrated at 500 ±C for 4 h. It exhibits a dielectric constant of 1024 and a dielectric loss of 2.1% at a frequency of 1 kHz at room temperature. A calcination at a too-high temperature, e.g., 600 ±C, results in a reduction in the sinterability of the precipitate-derived PZT ceramic.
I. INTRODUCTION
Lead zirconate titanate (PZT) is technologically important in electronics and microelectronics due to their excellent piezoelectric, ferroelectric, and many other electrical properties. High density and uniform microstructure are among the most desirable features for PZT and PZT-based electroceramics in obtaining many of these most wanted electrical properties. It is, however, difficult to achieve a sintered density close to the theoretical density via conventional ceramic processing routes using the mixed oxides as the starting materials. This, together with many of the undesirable features of sintered PZT, such as the nonstoichiometry in composition and wide fluctuation in composition and poor microstructure, is due to the loss in lead content during the calcination and sintering processes as a result of the high volatility of PbO at elevated temperatures.1 It is therefore desirable to process PZT and PZT-based ceramic materials at a temperature as low as possible, in order to alleviate, if not completely eliminate, these problems. One approach is the use of ultrafine ceramic powders as the starting materials, which may be synthesized via several chemistry-based novel preparation routes, such as oxalate route,2 co-precipitation,3,4 hydrothermal reaction,5 alkoxide hydrolysis,6 to name a few of the
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14,
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