Journal of Crystal Growth 258 (2003) 211–222 Vibroconvective mixing applied to vertical Bridgman growth Kevin T. Zawilski a, *, M. Claudia, C. Custodio b,1 , Robert C. DeMattei b , Robert S. Feigelson a a Department of Materials Science and Engineering, Stanford University, McCullough Building, Rm 237, Stanford, CA 94305, USA b Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA Received 14 January 2003; accepted 25 June 2003 Communicated by J.J. Derby Abstract A promising method for stirring melts during vertical Bridgman growth is the coupled vibrational stirring (CVS) method. It involves the application of low frequency vibrations to the outside of the growth ampoule and produces strong flows emanating from the fluid surface. Although the technique was pioneered a number of years ago, previous studies have not provided sufficient information to explain how to control CVS generated flows in a particular system. This paper examines both the fluid flow produced by CVS and the effect of these flows on a model oxide growth system. CVS generated flows were studied using tracer particles in a water/glycerin system. The particle velocities were measured as a function of distance from the fluid surface. A large velocity gradient, decreasing from the surface, was found to be present. The velocity profile produced was dependent on the vibrational amplitude and frequency, the crucible diameter, and the fluid viscosity. The effects of CVS flows on the crystal growth interface were studied using NaNO 3 as a model oxide. Under non-growth conditions (i.e. no furnace or crucible translation), the solid–liquid interface position was found to be a strong function of vibrational frequency once CVS generated flows approached the interface. During crystal growth, undesirable growth rate fluctuations were found as the growth interface moved into regions of increasing fluid flow. This data suggests that a control system in which CVS flows are continuously decreased during growth to maintain a constant flow rate in the vicinity of the growth interface is necessary in order to prevent or reduce growth rate fluctuations. r 2003 Elsevier B.V. All rights reserved. Keywords: A1. Convection; A1. Directional solidification; A1. Fluid flows; A1. Stirring; A2. Bridgman technique; B1. Oxides 1. Introduction Fluid convection affects heat and mass trans- port during crystal growth from the melt. It often occurs spontaneously under the influence of gravity when temperature and concentration gradients are present. While this ‘‘natural’’ con- vection can be beneficial, it often adversely affects growth because it is uncontrollable and frequently unstable (often oscillatory) [1–3]. On the other hand, forced convection (i.e. stirring) is used in many crystal growth systems to improve crystal quality and growth rates by introducing controlled flows to the melt [1–6]. Controlling the convection ARTICLE IN PRESS *Corresponding author. Tel.: +6507234874; fax: +6507233752. E-mail address: zawilski@stanford.edu (K.T. Zawilski). 1 Present address: Crystal Technology, Inc., 1040 East Meadow Circle, Palo Alto, CA 94303, USA 0022-0248/$-see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0022-0248(03)01507-0