Observation of a dodecagonal oxide quasicrystal and its complex approximant in the SrTiO 3 -Pt(1 1 1) system

We report on the formation of a SrTiO 3 -derived dodecagonal oxide quasicrystal (OQC) at the interface to Pt(1 1 1). This is the second observation of a two-dimensional quasicrystal in the class of oxides. The SrTiO 3 -derived OQC exhibits strong similarities to the BaTiO 3 -derived OQC with respect to the local tiling geometry. However, the characteristic length scale of the SrTiO 3 -derived OQC is 1.8% smaller. Coexisting with the OQC a large scale approximant structure with a monoclinic unit cell is identified. It demonstrates the extraordinary level of complexity that oxide approximant structures can reach.