On the reaction of Pt with SiO2 substrates : observation of the Pt3Si phase with the Cu3Au superstructure

The reaction of platinum with SiO2 substrates during thermal treatment in hydrogen has been studied by electron microscopy, electron diffraction and microdiffraction. Following prolonged heating at 840 K in H2 a new Pt-Si phase with the cubic Cu3Au structure (a=0.388 nm, Pm3̄m space group) could be identified. This phase can be transformed into the monoclinic Pt3Si alloy after heating at higher temperatures. The formation of the cubic structure is interpreted in terms of a platinum rich Pt3Si phase which is intermediate to the monoclinic Pt3Si.