L Journal of Alloys and Compounds 308 (2000) 139–146 www.elsevier.com / locate / jallcom Synthesis of lead zirconate titanate from an amorphous precursor by mechanical activation * Xue Junmin, John Wang , Toh Weiseng Department of Materials Science, Faculty of Science, National University of Singapore, Singapore 119260, Singapore Received 24 March 2000; accepted 25 April 2000 Abstract Many of the chemistry-based processing routes for functional ceramics inevitably involve calcining the chemical-derived precursors at an intermediate / high temperature, in order to form the designed ceramic phase. This is very undesirable, although widely used, as the calcination can result in an extensive degree of crystal growth and particle coarsening at the calcination temperature and therefore ruins almost all the advantages offered by the chemistry-based processing routes, such as an ultrafine particle size and high sintering-reactivity. Using a specifically designed PZT precursor prepared by co-precipitation, it is demonstrated that the precursor-to-ceramic conversion can alternatively be realized by mechanical activation. In this connection, a single phase, nanocrystalline perovskite PZT powder has been successfully derived from an amorphous hydroxide precursor by mechanical activation. The resulting PZT powder was well dispersed, and the particle size was in the range of 30–50 nm, as observed using the scanning electron microscopy and transmission electron microscopy. This is in contrast to the poor particle characteristics, represented by very coarse and irregular particle and agglomerate sizes, for the powder derived from calcination at 7508C. The activation-triggered PZT powder was sintered to a density of 97.6% theoretical density at 11508C for 1 h. Sintered PZT ceramic exhibits a dielectric constant of 927 at room temperature and a peak dielectric constant of |9100 at the Curie point of 3808C when measured at the frequency of 1 kHz.  2000 Elsevier Science S.A. All rights reserved. Keywords: Lead zirconate titanate; Nanopowders; Mechanical activation; Dielectric properties; XRD 1. Introduction position of the resultant PZT often occurs as a result of the undesirable loss in lead content through volatilization of Lead zirconate titanate, Pb(Zr,Ti)O (PZT) of perov- PbO at elevated temperatures [4]. Many chemistry-based 3 skite structure, which was found to be piezoelectric in the processing routes, such as the oxalate route [5], co-precipi- 1950s, is widely used in various sensing and actuating tation [6], alkoxide hydrolysis [7] and hydrothermal re- devices [1]. They are often fabricated by first preparing a action [8], have thus been devised and employed to prepare fine and homogeneous PZT powder, followed by shape- ultrafine and sintering-reactive PZT powders. However, forming and sintering at an appropriate temperature to almost all of these chemistry-based processing routes achieve the required sintered density, microstructure and require the precursors be calcined at a temperature in the electrical properties [2]. The traditional method of syn- range of 600–9008C, in order to develop the designed PZT thesizing PZT powder is through solid-state reaction, perovskite phase. This often results in a considerable which involves mixing the constituent oxides (PbO, TiO degree of particle coarsening and agglomeration and thus 2 and ZrO ) in stoichiometric ratio, followed by calcination ruins the sintering-reactive nature of chemical-derived 2 for phase formation at an elevated temperature ( .7008C) precursors. In fact, the presence of hard particle aggregates [3]. However, this often leads to an incomplete reaction, adversely affects the sintering and microstructural develop- and in particular, particle coarsening and agglomeration in ment of PZT at the sintering temperature when differential the resulting PZT powder as a result of the multiple sintering among aggregates of differing green density interfacial diffusions and reactions involved at the calcina- occurs. tion temperature. Furthermore, nonstoichiometry in com- Following the pioneer work of Benjamin [9], who devised mechanical alloying for synthesizing novel nanocrystalline metal and alloying powders, there has been *Corresponding author. Tel.: 165-874-2958; fax: 165-776-3604. E-mail address: maswangj@nus.edu.sg (J. Wang). a surge of interest in mechanical activation over the past 0925-8388 / 00 / $ – see front matter  2000 Elsevier Science S.A. All rights reserved. PII: S0925-8388(00)00917-8