Chemical ordering in PtNi nanocrystals

We investigated the chemical ordering in PtNi nanocrystals fabricated on sapphire substrate using in-situ synchrotron X-ray scattering. Nanocrystals with composition close to 1:1 were ordered in the tetragonal L10 structure at low temperatures. The transition to disordered FCC structure occurred at around 640 °C and substantial hysteresis of about 50 K was observed. Nanocrystals of smaller sizes fabricated under the same conditions were Ni rich and ordered into Cu3Au type L12 structure. Significantly higher degree of chemical ordering was observed in L12 structure than in L10 structure.