Short communication Microwave-hydrothermal synthesis of barium titanate under stirring condition Sridhar Komarneni a, * , Hiroaki Katsuki b a Materials Research Institute and Department of Crop and Soil Sciences, 205 Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA b Saga Ceramics Research Laboratory, 3037-7, Arita-machi, Saga 844-0022, Japan Received 1 October 2009; received in revised form 13 October 2009; accepted 22 November 2009 Available online 4 January 2010 Abstract The role of in situ stirring under microwave-hydrothermal (M-H) conditions on the synthesis of barium titanate was investigated for the first time by powder X-ray diffraction and scanning and transmission electron microscopy. Stirring under M-H conditions in the temperature range of 150–200 8C led to enhanced crystallization of Ba titanate as revealed by yields compared to the static condition. In addition, stirring led to smaller and more uniform crystals under M-H conditions compared to those crystallized without stirring. Powder X-ray diffraction revealed the formation of only cubic polymorph of Ba titanate at or below 200 8C in 4 h with or without in situ stirring under M-H conditions. These results show that stirring is an important parameter during M-H synthesis of nanophase Ba titanate. # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: Barium titanate; Cubic phase; Ferroelectric; Microwave-hydrothermal synthesis; Stirring 1. Introduction Barium titanate is by far the largest amount of dielectric material used in the ceramic capacitor industry. It is also a ferroelectric material with piezoelectric properties although lead zirconate titanate (PZT) replaced Ba titanate because PZT has better piezoelectric properties. Ba titanate material is widely used in multi-layer ceramic capacitors (MLCCs), piezoelectric and ferroelectric devices, positive temperature coefficient (PTC) thermistors, field-effect transistors, etc. Ba titanate has been prepared by the traditional solid-state process, sol–gel process and many other techniques including the hydrothermal process [1–3]. An excellent review of the various BT synthesis techniques was previously published [1]. Among these, the hydrothermal process is ideally suited for preparing nanopow- ders of Ba titanate (BT) and in fact, hydrothermally produced BT has been commercially sold [4] for several years. Nanophase Ba titanate is a necessity for making compact MLCCs. The main advantages of the hydrothermal process are (a) it is a low temperature process, (b) it is an environmentally benign process as the processing is done under closed system conditions and (c) it is easy to control the size and shape of the particles. The conventional-hydrothermal process has been extensively used in single crystal as well as powder preparation for over a century because of the above advantages [5,6]. Over the years, there are a few modifications to the conventional-hydrothermal (C-H) www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 36 (2010) 1165–1169 Table 1 Microwave-hydrothermal (M-H) and conventional-hydrothermal (C-H) synthe- ses of BaTiO 3 . a . Reaction Yield b (%) of BaTiO 3 No stirring Stirring at 157 rpm M-H 150 8C—10 min 90.7 96.4 M-H 150 8C—60 min 91.3 97.7 M-H 180 8C—10 min 86.7 91.9 M-H 180 8C—30 min 89.5 94.5 M-H 180 8C—120 min 95.9 96.4 M-H 200 8C—15 min 93.1 97.2 M-H 200 8C—2 h – 97.4 M-H 200 8C—4 h – 97.9 C-H 200 8C—24 h 96.6 – C-H 200 8C—48 h 97.2 – a Only cubic phase formed in all cases. b Yield (%) is calculated as the weight ratio of product obtained to that expected upon complete crystallization. * Corresponding author. Tel.: +1 814 865 1542; fax: +1 814 865 2326. E-mail address: Komarneni@psu.edu (S. Komarneni). 0272-8842/$36.00 # 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2009.12.016