The aim of our study is to analyze the surface of higher-temperature tetragonal (white) beta-tin, which tends to transform into stable alfa-tin (grey) under several conditions that have not yet been sufficiently explained. The beta-tin typically starts to transform upon cooling under 13.2°C, and its transformation rate accelerates with undercooling to its maximum at -53°C. But that process itself is taking an immensely long time (up to years). The transformation rate increases with the help of nucleation by alfa-tin particles (so-called inoculation) and pressure (resulting in a reduction of the transformation time to days and hours). The transformation also starts by helping the different types of compounds, e.g. CdTe, InSb, etc., and the pressure magnitude changes the transformation rate too. The surface of beta-tin is passivated by SnO the same way as the surface of Al and stainless steel by AlxOy and CrxOy.
We study the very thin passivating oxide layer by different methods, which are more sensitive to the surface than X-ray powder diffraction (XRPD), e.g. GIXRD, CEMS, XPS and FTIR. The surface study shows the SnO could also be nuclei of the whole transformation process.
The financial support from the Czech Science Foundation received under Project No. 22-05801S is gratefully acknowledged