DOE OSTI2020
Ta4C3 is MAX Phase-derived structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three Ta4C3 sheets oriented in the (0, 0, 1) direction. there are four inequivalent Ta3+ sites. In the first Ta3+ site, Ta3+ is bonded to six C4- atoms to form a mixture of distorted corner and edge-sharing TaC6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 1°. There are three shorter (2.26 Å) and three longer (2.27 Å) Ta–C bond lengths. In the second Ta3+ site, Ta3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.15 Å. In the third Ta3+ site, Ta3+ is bonded in a distorted T-shaped geometry to three equivalent C4- atoms. All Ta–C bond lengths are 2.20 Å. In the fourth Ta3+ site, Ta3+ is bonded to six C4- atoms to form a mixture of corner and edge-sharing TaC6 octahedra. There are three shorter (2.22 Å) and three longer (2.24 Å) Ta–C bond lengths. There are three inequivalent C4- sites. In the first C4- site, C4- is bonded to six Ta3+ atoms to form a mixture of corner and edge-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second C4- site, C4- is bonded to six Ta3+ atoms to form a mixture of corner, edge, and face-sharing CTa6 octahedra. The corner-sharing octahedral tilt angles are 47°. In the third C4- site, C4- is bonded to six Ta3+ atoms to form a mixture of corner, edge, and face-sharing CTa6 octahedra. The corner-sharing octahedra tilt angles range from 1–47°.