The pressure-induced phase transition in SnO: a first-principles study

The structural modifications of SnO within the tetragonal phase (alpha-SnO) and the orthorhombic phase (gamma-SnO) with pressure were extensively studied by using the first-principles pseudopotential plane-wave method within the generalized gradient approximation. A structural phase transition from alpha-SnO to gamma-SnO is predicted at 1.1 GPa by evaluating the enthalpy difference of the two crystal structures. During the transition, the volume changes continuously with increasing pressure, and a linear increase of the spontaneous strain is predicted. These facts indicated the second-order nature of this phase transition. Moreover, the pressure dependences of the Raman shift for both a-SnO and. SnO structures are presented to show further evidence for the phase transition. A softening B-1g mode with pressure is suggested to be the physically driven force of the transition. The current theoretical results strongly suggest the existence of gamma-SnO phase in SnO under high pressure.