Interfacial Mass Transfer and Morphological Instability of Oxide Crystal Growth

Abstract

Mass transfer near the solid-liquid interface is a fundamental problem in crystal growth and it is also a prerequisite for producing high-quality homogeneous crystals. It is desired that the mass transport phenomenon in the liquid phase can be visualized simultaneously with the growing interface. Such information is very helpful for the understanding of crystal growth mechanism. But little is known about the direct connection between mass transport and interfacial morphology in oxide crystal growth, mainly because it is technically difficult to visualize interface growth with mass flow in the high-temperature environment. In the present chapter of the book, we take high-temperature melt (or solution) growth of oxide crystal as an example, to study the interfacial mass transport and its effect on the interfacial morphology. Most of the results are based on the experiments performed in a high-temperature in situ observation system developed by the authors (W. Q. Jin, et al., 1993), which will be firstly introduced in the following. This system is designed specially for visualizing and recording the mass transport as well as the growth process under the condition of high temperature. After that we will show the typical buoyancy and Marangoni convections in-situ observed in high temperature oxide melt in a loop-like heater. The effect of convection on the thickness of interfacial boundary layer will also be demonstrated. Then, we will discuss the diffusion-induced microconvection near the solid-liquid interface and the mass transport in the boundary layer. The next section is devoted to deriving the correlation between the mass transfer and the interfacial morphology. After that, we shall see how external forces, such as magnetic field and mechanical vibration, stabilize the unsteady convection. Coupled with the help of external forces, effect of mass transfer near solid-liquid interface is optimized and then bulk oxide crystals with high quality are obtained by vertical zone-melting technique or vertical Bridgman growth technique. Finally, we will give a short summary and express our acknowledgments.