Exceptional surface stability in late transition metal alloys driven by lattice strain

Due to the lower compressibility of the close-packed crystallographic planes compared to the less close-packed ones, the open free surfaces of the late transition and noble metals are generally expected to become thermodynamically stable with increasing pressure. Surface segregation in concentrated alloys and heteroepitaxial growth are possible mechanisms to create additional lattice strain around the surface layer and, thus, alter the surface stability at ambient conditions. Here we demonstrate this phenomenon in the case of PdAg random alloys by performing ab initio density functional calculations for the surface energy and stress. Our findings reveal anomalous surface stability, so far experienced only in some magnetic transition metals, and exceptionally large excess surface stress as an indicator for surface reconstruction.