L Journal of Alloys and Compounds 340 (2002) 214–219 www.elsevier.com / locate / jallcom Characterization of hydrothermally prepared BaTi Zr O 1 2x x 3 a, a a a b * A. Outzourhit , M.A. El Idrissi Raghni , M.L. Hafid , F. Bensamka , Abdelkader Outzourhit a ´ ´ ´ Laboratoire des Sciences des Materiaux, Faculte des Sciences Semlalia, BP 2390, Universite Cadi Ayyad, Marrakech, Morocco b ´ ´ Laboratoire de Physique du Solide et des Couches Minces, Faculte des Sciences Semlalia, BP 2390, Universite Cadi Ayyad, Marrakech, Morocco Received 20 February 2001; accepted 30 November 2001 Abstract BaTiO (BTO) and BaTi Zr O (BZT) powders were prepared using the hydrothermal method, starting from BaO, TiO and 3 0.8 0.2 3 2 Zr(NO ) , 7H O. X-ray diffraction analysis showed that the cubic phase is stable at room-temperature and the pure perovskite phase is 3 2 2 obtained after heating the powders for 2 h at 1280 8C. The temperature dependence of the dielectric constant points to ferroelectric behavior. This ferroelectric behavior can likely be due to the presence of a possible quadraticity gradient in the grains since the cubic phase may not be ferroelectric. The diffuse character of the transition is attributed to this quadraticity gradient, to grain size distribution and (for BZT) to spatial fluctuations in the concentrations of the substituted ion (Zr) leading to the coexistence of regions of different Curie temperatures.  2002 Elsevier Science B.V. All rights reserved. Keywords: Ferroelectrics; Chemical synthesis; X-ray diffraction; Dielectric response 1. Introduction esting electrical properties. The preparation of BTO ceramics by wet chemical methods has been reported in Ferroelectric materials are increasingly used in elec- the literature. Among these techniques, the mostly used tronic and optoelectronic devices [1,2]. These materials methods are the hydrothermal process [11–21] and the cover a wide spectrum of applications ranging from simple sol–gel method [22–24]. dielectric capacitors to optical devices, piezoelectric filters, In this work, BaTiO (BTO) and BaTi Zr O (BZT) 3 0.8 0.2 3 pyro-electric detectors and acoustic transducers [2,3]. ceramics were synthesized by the hydrothermal technique. In particular, barium titanate (BaTiO ) ceramics, re- The structural and dielectric properties of the obtained 3 ferred to hereafter by BTO, are interesting because they materials are presented. The major advantage of this present a simple structure and their properties can be easily method is the moderate temperature employed during the controlled by introducing doping elements into the cationic synthesis (140 8C) and the inexpensive reactors used to 41 sub-lattice [4,5]. For example, the replacement of Ti by reduce the cost of the products. In addition, the resulting 41 Zr changes significantly the electrical and structural fine powders have improved sintering characteristics. properties of BaTiO . This allows to increase the ortho- 3 rhombic-tetragonal transition temperature and to decrease the Curie point [6]. Such changes are usually accompanied 2. Materials and methods by variation in the dielectric, electrical and optical prop- erties of the ceramics which can then be easily tailored to The flow diagram of the preparation method used in this specific applications. work is shown in Fig. 1. A solution of Ba(OH) is 2 The conventional method used for the preparation of prepared by dissolving barium oxide (BaO, 99.9%) in electronic ceramics is the solid-state reaction (SSR) meth- distilled water. On the other hand, zirconium nitrate od [7,8]. This technique is increasingly replaced by wet Zr(NO ) , 7H O was dissolved in water and ammonium 3 2 2 methods which, although still costly, have the advantage of hydroxide (NH OH) was subsequently added to this 4 yielding a higher purity and a more uniform grain size and solution to promote the formation of a ZrO , yH O precipi- 2 2 composition [9,10]. In addition, these techniques lead to tate. The mixture of Ba(OH) , TiO , and ZrO , yH O in 2 2 2 2 denser microstructures with smaller grain sizes and inter- appropriate amounts is then introduced in a Teflon-lined autoclave in the presence of sodium hydroxide (NaOH). *Corresponding author. Subsequently, the reactor is heated to a temperature 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01986-7