Novel stable hard transparent conductors in TiO₂-TiC system: design materials from scratch.

Two new ternary compounds in the TiO2-TiC system, Ti5C2O6 and Ti3C2O2, are reported for the first time based on ab initio evolutionary algorithm. Ti5C2O6 has a tube-structure in which sp(1) hybridized carbon chains run through the lattice along the b-axis; while in the Ti3C2O2 lattice, double TiO6 polyhedral are separated by the non-coplanar sp(2) hybridized hexagon graphite layers along the c-axis, forming a sandwich-like structure. At ambient conditions, the two compounds are found to be mechanically and dynamically stable and intrinsic transparent conductors with high hardness (about twice harder than the conventional transparent conducting oxides). These mechanical, electronic, and optical properties make Ti5C2O6 and Ti3C2O2 ternary compounds be promising robust, hard, transparent, and conductive materials.