New aspects of axial-to-planar channeling transition in a noncubic compound crystal, $\alpha$-${\mathrm{Al}}_2$${\mathrm{O}}_3$

The axial-to-planar channeling transition in $\alpha$-${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ has been studied both experimentally and by computer simulation for various axes and planes. Particular interest has been turned to the $〈0001〉\to \left\{1\mathrm{}\overline{2}10\right\}$ transition, characterized by a shoulder, for the O sublattice, much higher than 100%. Both experiments and calculations, the latter carried out also varying the lattice arrangement, show that these shoulders are determined by the mutual flux peaking due to the two sublattices. In particular, calculations show that the relative spacing between the two sublattices in the real crystal is such as to maximize the effect. Computed trajectories are in agreement with the model of resonance dechanneling by Kumakhov and Wedell.