LiNbO3晶体-熔体界面的失稳及向胞状界面演化的实验研究

利用周期旋转生长条纹作为时标(timemarker),研究了直拉法掺钇LiNbO₃的各向异性生长系统中晶体-熔体界面的失稳及向胞状界面的演化。测得平界面失稳的临界条件,观测到失稳初期的界面上存在的两种干扰,即正弦式干扰和正弦式行波干扰。实验结果表明,平界面失稳后,经历正弦干扰、干扰振幅的增长、干扰的小面化、干扰的合并,最后演化为稳态胞状界面。实验观测还表明,稳态胞状界面的波长甚大于界面初始干扰的波长,且为初始干扰波长的整数倍;以及同一系统中平界面向胞状界面转变的临界生长速度小于胞状界面向平界面转变的临界速度,这表明小面化的胞比非小面的平面更为稳定。关键词：

EXPERIMENTAL INVESTIGATION OF STABILITY OF PLANAR CRYSTAL-MELT INTERFACE AND EVOLUTION OF CELLULAR INTERFACE DURING CZOCHRALSKI GROWTH OF LiNbO3 SINGLE CRYSTALS DOPED WITH YTTRIUM

By using periodic rotational striations as a time marker, the initial instability of a planar interface and the development of the cellular interface have been studied in Czochralski growth system of anisotropic LiNbO₃ crystals doped with yttrium. The critical condition for very birth of instability of planar interface has been obtained. And there are two kinds of initial perturbations to be observed, that is, sinusoidal perturbation and sinusoidal travelling wave perturbation. Experimental results revealed that the planar interface evolves from sinusoidal perturbation to facetted perturbation to coarse facetted perturbation, finally, to stable cellular interface. It has been found that the wave-length of stable cellular interface is different from that of initial perturbation and always integral times larger than that of initial one. There is also a difference to be found between critical velocity of the plane-to-cell transition and that of cell-to-plane transition for a same crystal grown from the same system. It may be implied that the facetted cell is more stable than the nonfacetted plane.