Phase Relations of Iron Carbides Fe₂C, Fe₃C, and Fe₇C₃ at the Earth’s Core Pressures and Temperatures

—Based on first-principle calculations in the framework of the density functional theory and structure prediction algorithms, we have determined iron carbide phases stable at the Earth’s core pressures and temperatures. It is shown that Fe₇C₃ is unstable and decomposes into the mixture Fe₂C + Fe₃C over the entire range of pressures and temperatures specific to the Earth’s inner core. Subsequent decomposition of Fe₃C into the mixture Fe + Fe₂C is unfavorable. We also predict a new low-temperature modification Fe₃C-C2/m-II dynamically and thermodynamically stable over the pressure range 290–305 GPa.