Modification of the micro-pulling-down method for high-temperature solution growth of miniature bulk crystals

doi:10.1016/j.jcrysgro.2004.11.030

Journal of Crystal Growth

Volume 275, Issues 1–2, 15 February 2005, Pages e867-e870

https://doi.org/10.1016/j.jcrysgro.2004.11.030 Get rights and content

Abstract

An effective use of the micro-pulling-down (μ-PD) growth method for high-temperature solution growth is shown to be feasible due to very strong Marangoni convection in the μ-PD meniscus. Modifications in the crucible geometry and in the growth procedure allow the growth of fiber samples in which an excessive flux is periodically captured, or even miniature bulk single crystals completely free of flux inclusions. This is demonstrated by successful growth of LiTb_0.9Eu_0.1P₄O₁₂ from LiPO₄ flux.

Introduction

The micro-pulling-down (μ-PD) method which has been developed at the Fukuda Laboratory of Tohoku University [1] is usually believed as being suitable only for melt growth of congruently melting compounds. Since the melt is delivered to the growth interface through the narrow capillary channel, only the diffusion controlled growth mode is considered [2]. In such case an effective distribution coefficient should always be equal to unity, and the melt and crystal compositions will be always equal, as it happens in the edge-defined film-fed (EFG) growth of bulk shaped crystals. However, this consideration does not take into account, that in the μ-PD the cross-sections of the capillary, the meniscus and the narrow fiber crystal itself are almost the same. Together with very intensive melt mixing in the meniscus cased by thermocapillary convection, this opens the possibility to use the μ-PD also for incongruent melts, or for solution growth, as it will be shown below. It should be mentioned, that the first successful attempt to use the μ-PD for solution growth of KNbO₃ has been made by Chani et al. in Ref. [3].

Section snippets

Melt stirring in μ-PD growth

The beneficial effect of melts stirring on the achievement of stable growth at high growth rates typical for the μ-PD method, comes from the reduction of the interface boundary layer thickness. As shown by Elwell and Scheel [4] an increase in the rate of solution flow along the interface surface always leads to stabilization, since the local temperature gradient on the interface is steepened by stirring to a greater extent than the solute gradient (see for details Chapter 6 in Ref. [4]). This

Discussion and conclusions

It is often discussed if the μ-PD method can be considered as a particular crystal growth method or it is just a miniaturized (and also turned up-side-down) version of the EFG method. On our opinion, the case of μ-PD is a convincing demonstration of how the miniaturization can bring about sufficiently new properties. The method of μ-PD in no case can be considered as a version of EFG at least because of totally different manner of segregation in the μ-PD. It may sound curious, but at least in

Acknowledgements

This work has been supported in part by Deutsche Forschungsgemeinschaft (DFG). The authors cordially acknowledge Prof. T. Fukuda of IMRAM of Tohoku University for stimulating discussions on the topic of μ-PD growth.

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Modification of the micro-pulling-down method for high-temperature solution growth of miniature bulk crystals

Abstract

Introduction

Section snippets

Melt stirring in μ-PD growth

Discussion and conclusions

Acknowledgements

J. Crystal Growth

J. Crystal Growth

J. Crystal Growth

Radiat. Meas.

Crystal Res. Technol.