Journal of Sol-Gel Science and Technology 15, 13–22 (1999) c  1999 Kluwer Academic Publishers. Manufactured in The Netherlands. A Comparison of the Nanostructure of Lead Zirconate, Lead Titanate and Lead Zirconate Titanate Sols Q. ZHANG AND R. WHATMORE Advanced Material Group, Cranfield University, SIMS, Cranfield, Beds, MK43 0AL, UK M.E. VICKERS Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB2 3QZ, UK Received September 8, 1997; Accepted December 29, 1998 Abstract. Sol-gel processing has been widely used for the fabrication of lead zirconate titanate (PZT) thin films. To successfully and consistently make high quality thin films for different applications, we must develop a fundamental understanding of the structures of the sols. In this study, the characters of lead titanate (PT) and lead zirconate (PZ) sols were studied by measuring the rheological properties and particle sizes in them and comparing their behaviours. The average particle sizes in unhydrolysed PT, PZ and PZT sols are 11.5, 1.0, and 6.0 nm, respectively. PT sol has the highest rate of hydrolysis. It gels at about 24 h after hydrolysis. PZ and PZT sols have a quite similar feature in hydrolysis. The reasons for the differences in the hydrolysis behaviour of the different types of sol are discussed in terms of a model which indicates that the inhomogeneous sols consist of 5 to 6 nm PT particles surrounded by much smaller PZ particles, which tend to dominate the sol behaviour. Keywords: precursor chemistry, lead zirconate titanate, hydrolysis, PCS, SAXS 1. Introduction Ferroelectric lead zirconate titanate (PZT) thin films have potential applications for integrated devices such as ferroelectric memories, infrared sensors and micro- actuators [1–5]. Sol-gel processing has been widely used to make PZT thin films because it can provide relatively easy control of composition. The uses of organometallic starting materials, additives, solvents, and even the route of synthesis are frequently chosen empirically, leading to the layers having a wide range of electrical properties. Therefore, a basic understanding of sol physics and chemistry, starting from precursor solutions to the development of the desired crystalline microstructures is very desirable for industrial scale manufacture of good quality PZT thin layers with re- producible properties. The first step of sol-gel processing includes the mix- ture of the starting metal precursors in a pure solvent or a hybrid solvent. It is normally thought that this mixture would lead to the formation of a new multimetal com- plex and all the metal atoms would be bonded to one another through oxygen atoms or organic ligands at the molecular level. However, in some cases, such a mix- ture of starting materials leads to a heterogeneous sol [6]. The resulting thin films spin- or dip-coated by us- ing such a solution appear to have cracks and/or pores after the final annealing due to the different thermal shrinkage of inhomogeneous unhydrolysed oligomeric species in solution, which damages the ferroelectric properties of the films [7]. For the synthesis of PZT alkoxide complexes, the synthesis routes, for example the mixing order of start- ing metal precursors and the choice of solvents, play an important role in the preparation of a molecule-level homogeneous sol. Frequently, it has been found that when Ti alkoxide mixes with Pb acetate in a hybrid solvent of alcohol and acetic acid, titanium alkoxide reacts with acetic acid to form mono or diacetates and condensation occurs with the formation of polytitanyl