Morphology and etch figures of a Yb:YAl_3(BO_3)_4 crystal

摘要

Yb:YAl_3(BO_3)_4 is a good self-frequency-doubling crystal with the point group 32. In this paper, atomic force microscopy (AFM) has been used to observe the etch figures of the three forms (positive trigonal prism {1120}, negative trigonal prism {2110} and rhombohedron {10111) on the crystal morphology of Yb:YAl_3(BO_3)_4. The etch figures display the point group 32 of the Yb:YAl_3(BO_3)_4 crystal. To compare the morphology and etch figures of Yb:YAl_3(BO_3)_4 with those of quartz, the classic crystal of point group 32, the etch figures of the three forms (hexagonal prism {1010}, positive rhombohedron {1011} and negative rhombohedron {0111}) on quartz were also observed using AFM. It is interesting that Yb:YAl_3(BO_3)_4 develops two prismatic forms (related by a positive–negative relationship) and one rhombohedral form, while quartz develops one prismatic form and two rhombohedral forms (also related by a positive–negative relationship). Etch figures of faces or sections with the same indices (or the same crystallographic orientations) in Yb:YA1_3(BO_3)_4 and quartz are very similar, although their crystal structures are very different. Besides diffraction methods, etch figures are a useful method for determining the point group of a crystal.