The high oxygen activity of perovskites makes them effective as solid oxide fuel cell (SOFC) cathodes. However, surface cation precipitation, especially Sr segregation, on La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathodes is a well-known issue that limits the cathode stability. Moreover, CO₂ is known to cause cathode degradation, but how CO₂ affects surface cation segregation is still unclear. Here, the formation of Sr-rich secondary phases on the surface of LSCF were evaluated systematically in a variety of conditions; including time, temperature, and oxygen partial pressure. This was done to better understand the mechanism and the contribution of each variable to surface cation segregation. Additionally, the CO₂ effect on the SrO segregation is also discussed. Our results demonstrate that SrO segregation on LSCF is thermodynamically favored as temperature increases, and a different segregation mechanism is observed above 850 °C. The nucleation sites are also determined, and the 3-step surface segregation process of nucleation, surface migration, and agglomeration, is proposed. We also observed that different gases (N₂, O₂, and CO₂) have different effects on the surface segregation. Meanwhile, the effects of underlying grain orientation on surface cation segregation is further discussed.