Flux growth mechanisms of PZT cubic grains S. Devemy ⁎, C. Courtois, P. Champagne, G. Moreau, A. Leriche Université Lille Nord de France, F-59000 Lille, France UVHC, LMP, F-59600 Maubeuge, France abstract article info Available online 25 August 2010 Keywords: Flux PZT Mechanism Texture Growth Growth in a PbO flux is an appropriate method to synthesize large cubic grains of Pb(Zr x Ti 1-x )O 3 . An application could be PZT-based piezoceramics texturation. In order to optimize this synthesis, the flux synthesis has to be understood. In this study, water quenchings of PbO flux synthesis were realized at every stage of the thermal cycle including 6 steps. The oxide powders (PbO, ZrO 2 and TiO 2 ) were mixed and quickly heated up to 1200 °C for 2 h. The flux was then slowly cooled down to 900 °C for 10 h. Further cooling down to 750 °C was followed by a natural cooling to room temperature. SEM observations, X-EDS analysis and X-ray diffraction were performed on the PZT powders after each quench showing several specific growth sequences. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. 1. Introduction Lead zirconate titanate (PZT) ceramics are materials usually used for their good piezoelectric properties. The PZT properties optimiza- tion by adding doping agents is well known [1]. At this stage, to further increase the piezoelectric response, it is possible to develop a preferential crystalline orientation into the ceramic. Such a micro- structure can be obtained by both the synthesis in large and facetted grains and a tape-casting procedure [2–4]. Many works have shown that the PbO flux method is an appropriate process to synthesize large and facetted grains. This synthesis allowed to obtain large and cubic-like shaped grains of several types of perovskite structures as PT [5–7] or PMN-PT [3,8,9] using a PbO flux. More recently, grains of PZT have been synthesized in a PbO flux method [10–12]. The PZT solid solution presents a morphotropic phase transition near the X = 0.53 with x = Zr / (Ti + Zr) composition for which very good piezoelectric properties are observed. By using a flux method, we have shown [12] that it was not possible to synthesize cubic shape and coarse grains with the morphotropic composition. Nevertheless, it was demonstrated that such shaped grains can be obtained in the tetragonal area. It is expected that better piezoelectric response may be obtained by texturing the ceramic despite of a composition out of the morphotropic one and in the tetragonal one. These grains exhibited a cubic shape and a size between 50 and 70 μm. Size and shape were not good enough to enhance sufficiently their specific orientation during tape-casting. In order to optimize this synthesis route, we propose to investigate it by performing quenching at different steps of the synthesis protocol followed by appropriate observations and characterizations of the product. At the end, it is expected to clarify some of the precipitation mechanisms. The thermal cycle consists in 6 steps: a quick heating up to 1200 °C, a first dwell at this temperature during 2 h, a cooling down to 900 °C (60 °C/h) followed by a second dwell during 10 h, and a slow cooling down to 750 °C at a rate of 5 °C/h. The crucible is then cooled to room temperature. The target composition was X = 0.44. Between each step of the thermal process, the synthesis was abruptly stopped by water quenching. Grains were extracted from the solid melt and character- ized SEM observations, X-EDS analysis and X-ray diffraction measurements. 2. Experimental procedure The raw materials are reagent-grade PbO (Massicot, MERCK), TiO 2 (Anatase, LABOSI, N 99%) and ZrO 2 (Baddeleyite, ALDRICH, N 99%). Weighed powders were mixed using a planetary mill and then put in a platinum crucible. Molar composition and flux ratio are as follow: Zr/ Ti + Zr = 0.44, Flux/equivalent PZT = 60/40. For the following it is verified that Pb/(Zr + Ti) = 1 in the synthesized perovskite grains whatever their structural form. For quenching process, the crucible was taken up of the furnace and immersed as quick as possible in cold water. The different quenching temperatures are presented in Table 1. After quenching, the powder was milled with an agate mortar and pestle, washed with diluted acetic acid and dried at 100 °C for 12 h. Scanning electron micrographs of the powders were obtained on a HITACHI S-3500 N SEM, followed by a microanalysis with an X-EDS detector. Crystallization quality is analyzed by X-ray diffraction using a RIGAKU Miniflex diffractometer, parameterized in a speed of 1 s by Powder Technology 208 (2011) 351–354 ⁎ Corresponding author. UVHC, LMP, F-59600 Maubeuge, France. E-mail address: stephanie.devemy@univ-valenciennes.fr (S. Devemy). 0032-5910/$ – see front matter. Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2010.08.028 Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec