Abstract
Spiral steps observed on hematite crystals from Sasazawa, Nagano Prefecture, Japan show undulation of varying degrees depending on their heights and on the faces. Laboratorical etching produced etch hillocks, instead of etch pits, along the steps, corresponding to the undulation. At the summits of etch hillocks, crystallites of Mn–Ti rich phase were observed. From these, it was concluded that the observed step undulation was due to the precipitation of these crystallites, which played a role of obstacles against the advancement of spiral steps, and of heterogeneous two-dimensional nucleation site. The crystallites precipitated epitaxially on the {0001} surface, whereas they adhered selectively along the steps on the {10-11}. On the {11-20} surfaces, they selectively precipitated along the cliff created by twinning, and played a role of heterogeneous two-dimensional nucleation sites.
