Morphology and etch figures of a Yb:YAl 3 (BO 3 ) 4 crystal

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 {110}, negative trigonal prism {20} and rhombohedron {101}) 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 {100}, positive rhombohedron {101} and negative rhombohedron {011}) 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:YAl 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.