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. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim