Stoichiometric lithium niobate (LiNbO₃, sLN) shows improved performance for a number of applications compared to the congruent crystal, because of its nearly perfect crystal lattice containing low concentration of intrinsic structural defects ([Nb_Li] < 0.01%). The photorefractive damage of sLN crystals is usually suppressed by less than 1mol% MgO doping. Optical device applications impose the growth of crystals in high quality and increased sizes.

Up to now methods have been applied for the preparation of sLN crystals, the one which resulted in the composition closest to 50% Li₂O is the high temperature top seeded solution growth (HTTSSG) method using potassium oxide containing flux [1]. Crystals grown by this technique show a pronounced tendency towards faceting. Pyramidal facets formed in sLN deteriorate the crystal quality, as the related strains may induce domain inversion, mechanical twinning and cracks. Faceted growth may enhance incorporation of flux inclusions and bubbles as well [2]. Near planar solid liquid interface can be ensured by applying gradually variable rotation rate all along the crystal growth process resulting in non-faceted crystal growth [3].

In this work we present investigations on the characteristics of the melt flow patterns during the growth process of Mg-doped sLN crystals from Li₂O–Nb₂O₅–K₂O flux (in diameter of 20-55 mm) using resistant heating furnace. Temperature gradient and fluctuations are measured in order to determine the Grashof and Reynolds numbers characterizing the flow patterns in the melt. A specific effort is made to determine the critical rotation rate and crystal diameter, optimal for establishing non-faceted growth.

References:

[1] K. Polgár, Á. Péter, L. Kovács, G. Corradi, Zs. Szaller: Growth of stoichiometric LiNbO₃ by Top seeded solution growth, J. Crystal Growth, vol. 177, pp. 211-216 (1997)

[2] K. Polgár, Á. Péter, I. Földvári, Zs. Szaller: Structural defects in flux grown stoichiometric LiNbO₃ single crystals, J. Crystal Growth, vol. 218, No.2-4, pp.327-333, (2000).

[3] Zs. Szaller, Á. Péter, K. Polgár, Gy. Szabó: High temperature top seeded solution growth of stoichiometric lithium niobate LiNbO₃ (sLN) with planar interface,  J. Crystal Growth vol. 360 pp181-184 (2012)

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29754 must be provided.

1. Phase relations in the growth of stoichiometric LiNbO₃