Pressure-composition phase diagram of Ti-C from first principles

In this paper, we report a theoretical prediction of the zero-temperature pressure-composition phase diagram for the binary Ti-C system using ab initio evolutionary methodology. Our ground state search successfully identifies the known stable Ti₂C, Ti₃C₂, Ti₆C₅, and TiC structures at 0GPa. Our study uncovers two new titanium carbides that are thermodynamically stable at high pressures: tetragonal Ti₂C with I4/m symmetry and tetragonal Ti₃C₂ with P4/mbm symmetry. Both carbides are quenchable to ambient pressure and remain mechanically stable, and are potential candidates for hard materials. The I4/m and P4/mbm structures are also expected to be stable in the isoelectronic Zr-C and Hf-C systems at high pressures. Experimental synthesis of these novel carbides will be of great interest.