On the reaction of Pt with SiO sub(2) substrates: Observation of the Pt sub(3)Si phase with the Cu sub(3)Au superstructure

The reaction of platinum with SiO sub(2) substrates during thermal treatment in hydrogen has been studied by electron microscopy, electron diffraction and microdiffraction. Following prolonged heating at 840 K in H sub(2) a new Pt-Si phase with the cubic Cu sub(3)Au structure (a = 0.388 nm, Pm3m space group) could be identified. This phase can be transformed into the monoclinic Pt sub(3)Si alloy after heating at higher temperatures. The formation of the cubic structure is interpreted in terms of a platinum rich Pt sub(3)Si phase which is intermediate to the monoclinic Pt sub(3)Si.