Mechanism of solid-state amorphization of Se induced by mechanical milling

In this work, the solid-state amorphization process of elemental trigonal Se via mechanical milling was studied. Trigonal Se has a unique crystal structure consisting of helical [–Se–]n chains with strong intrachain covalent bonds and with weak interchain van der Waals bonds. It was found that the interchain coordination distance increased while the intrachain coordination distance decreased with increasing milling time. The crystalline Se transformed to the amorphous state once the interchain coordination distance reached a critical value. The intrachain coordination distance of amorphous Se continued to decrease with milling time, suggesting that molecular chain length decreased with milling time. Combined with the x-ray absorption near-edge structure calculations, it was concluded that the mechanical milling destroyed the interchain bonds of crystalline Se, resulting in the amorphization, while the intrachain bonds were strengthened during amorphization. The present results support a previous crystallite-destabilization model for solid-state amorphization.