DOE OSTI2020
Mg30TiBO32 is Molybdenum Carbide MAX Phase-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are eight inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent MgO6 octahedra, corners with two equivalent TiO6 octahedra, corners with two equivalent BO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.00–2.19 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four equivalent MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.12 Å) and two longer (2.15 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Mg–O bond distances ranging from 2.12–2.15 Å. In the fourth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with two equivalent BO6 octahedra, corners with four equivalent MgO6 octahedra, and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.02 Å) and four longer (2.15 Å) Mg–O bond lengths. In the fifth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one TiO6 octahedra, an edgeedge with one BO6 octahedra, and edges with ten MgO6 octahedra. The corner-sharing octahedra tilt angles range from 3–10°. There are a spread of Mg–O bond distances ranging from 2.09–2.19 Å. In the sixth Mg site, Mg is bonded to six O atoms to form a mixture of edge and corner-sharing MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–3°. There are two shorter (2.12 Å) and four longer (2.15 Å) Mg–O bond lengths. In the seventh Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one TiO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–5°. There are a spread of Mg–O bond distances ranging from 2.11–2.16 Å. In the eighth Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with six MgO6 octahedra, an edgeedge with one BO6 octahedra, and edges with eleven MgO6 octahedra. The corner-sharing octahedra tilt angles range from 1–9°. There are a spread of Mg–O bond distances ranging from 2.11–2.16 Å. Ti is bonded to six O atoms to form TiO6 octahedra that share corners with six MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.08 Å) and two longer (2.12 Å) Ti–O bond lengths. B is bonded to six O atoms to form distorted BO6 octahedra that share corners with six MgO6 octahedra and edges with twelve MgO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.26 Å) and four longer (2.27 Å) B–O bond lengths. There are eleven inequivalent O sites. In the first O site, O is bonded to five Mg and one Ti atom to form a mixture of edge and corner-sharing OMg5Ti octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with ten OMg6 octahedra, and edges with two OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 0–1°. In the third O site, O is bonded to five Mg and one B atom to form distorted OMg5B square pyramids that share corners with four equivalent OMg6 octahedra, corners with two equivalent OMg5B square pyramids, edges with eight OMg6 octahedra, and edges with four OMg5B square pyramids. The corner-sharing octahedral tilt angles are 4°. In the fourth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with six equivalent OMg6 octahedra, edges with nine OMg5Ti octahedra, and edges with three OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 1–4°. In the fifth O site, O is bonded to five Mg and one Ti atom to form OMg5Ti octahedra that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with ten OMg5Ti octahedra, and edges with two OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 0–3°. In the sixth O site, O is bonded to five Mg and one B atom to form distorted OMg5B square pyramids that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with eight OMg6 octahedra, and edges with four OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 6–8°. The O–Mg bond length is 2.00 Å. In the seventh O site, O is bonded to five Mg and one B atom to form distorted OMg5B square pyramids that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with eight OMg6 octahedra, and edges with four OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 6–8°. There are a spread of O–Mg bond distances ranging from 2.00–2.13 Å. In the eighth O site, O is bonded to six Mg atoms to form a mixture of edge and corner-sharing OMg6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. In the ninth O site, O is bonded to six Mg atoms to form OMg6 octahedra that share corners with four OMg6 octahedra, corners with two equivalent OMg5B square pyramids, edges with ten OMg6 octahedra, and edges with two equivalent OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 0–2°. In the tenth O site, O is bonded to five Mg and one B atom to form distorted OMg5B square pyramids that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with eight OMg6 octahedra, and edges with four OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 6–8°. Both O–Mg bond lengths are 2.13 Å. In the eleventh O site, O is bonded to five Mg and one B atom to form distorted OMg5B square pyramids that share corners with four OMg5Ti octahedra, corners with two equivalent OMg5B square pyramids, edges with eight OMg6 octahedra, and edges with four OMg5B square pyramids. The corner-sharing octahedra tilt angles range from 6–8°. There are two shorter (2.09 Å) and two longer (2.13 Å) O–Mg bond lengths.