Journal of Crystal Growth 306 (2007) 94–101 Growth, morphology and mechanism of rare earth vanadate crystals under mild hydrothermal conditions K. Byrappa a,Ã , C.K. Chandrashekar a , B. Basavalingu a , K.M. LokanathaRai b , S. Ananda b , M. Yoshimura c a Department of Geology, University of Mysore, Manasagangotri, Mysore 570 006, India b Department of Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India c Materials Structures Laboratory, Center for Materials Design, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama 226, Japan Received 18 July 2006; received in revised form 20 January 2007; accepted 8 March 2007 Communicated by T. Hibiya Available online 20 April 2007 Abstract Single crystals of RVO 4 (R ¼ Y,Gd) doped with optically active element like Nd have been obtained under mild hydrothermal conditions (T ¼ 240 1C, P80 bars). A detailed mechanism of the crystallization process, which helps in the considerable reduction of the PT conditions of the growth of these high-melting (m.p.41800 1C) crystals has been formulated. The crystals obtained have been subjected to morphological, X-ray powder diffraction and infrared spectroscopic studies. r 2007 Elsevier B.V. All rights reserved. PACS: 81.10.h; 42.70.Hj; 64.70Dv; 81.10.Aj Keywords: A1. Morphological stability; A2. Hydrothermal crystal growth; A2. Single crystal growth; B1. Rare earth compounds; B1. Vanadates; B2. Phosphors; B3. Solid state lasers 1. Introduction Growth of laser crystals is an attractive field in solid-state science owing to their technological significance. There exists a large number of solid-state laser host crystals from the family of phosphates, vanadates, fluorides, tungstates, etc. Amongst them, the yttrium orthovanadate-based laser- diode pumped solid-state lasers are the frontier materials and carry a wide variety of applications in science and technology because of its high stability, compactness, high efficiency and long life time [1–3]. Nd:YVO 4 crystals have been employed as highly efficient laser-diode pumped microlasers [4], an efficient phosphors [5], very attractive polarizer materials [6] and low-threshold laser hosts [7], etc. In comparison with the conventional Nd: YAG crystal, Nd:YVO 4 offers many advantages such as larger absorption co-efficient and gain cross section [8–10]. The rare earth vanadates are known as the high-melting materials (melting point 41800 1C) with low solubility and obviously their synthesis by any technique usually insists upon higher temperature conditions. That is one of the main reasons why most of the earlier workers have obtained these laser crystals by flux or melt methods [11–14]. In spite of its excellent physical properties, the high-tech applications have not been realized due to the crystal growth difficulties. One of the major problems encountered in the growth of RVO 4 crystals is the presence of oxygen imperfections (color centers and inclusions), which are introduced during the crystal growth processes. Although YVO 4 melts congruently [15], vanadium oxides vaporize incongruently, causing changes in Y/V ratio and oxygen stoichiometry in the melt. These undesired effects could generate additional phases and oxygen defects in theYVO 4 crystals grown especially from the melt [16]. Efforts to eliminate these defects did not yield significant success in the flux and melt techniques. Rubin and Vanuitert [11] were the first to obtain large bulk crystals ARTICLE IN PRESS www.elsevier.com/locate/jcrysgro 0022-0248/$ - see front matter r 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2007.03.055 Ã Corresponding author. Tel.: +91 821 2419720; fax: +91 821 2419720. E-mail address: byrappak@yahoo.com (K. Byrappa).