Materials Data on HfMg6BO7 by Materials Project

Abstract

Mg6HfBO7 crystallizes in the tetragonal P4mm space group. The structure is two-dimensional and consists of one Mg6HfBO7 sheet oriented in the (0, 0, 1) direction. there are four inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form distorted MgO6 octahedra that share corners with four equivalent MgO6 octahedra, corners with four equivalent MgO5 trigonal bipyramids, and edges with four equivalent MgO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 21°. There are a spread of Mg–O bond distances ranging from 1.99–2.31 Å. In the second Mg site, Mg is bonded to five O atoms to form distorted MgO5 trigonal bipyramids that share corners with eight MgO5 trigonal bipyramids and edges with four equivalent MgO6 octahedra. There are one shorter (2.04 Å) and four longer (2.10 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded in a T-shaped geometry to three O atoms. There are one shorter (2.03 Å) and two longer (2.04 Å) Mg–O bond lengths. In the fourth Mg site, Mg is bonded to five O atoms to form distorted MgO5 trigonal bipyramids that share corners with two equivalent MgO6 octahedra, corners with six MgO5 trigonal bipyramids, and edges with four equivalent MgO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 75°. There are a spread of Mg–O bond distances ranging from 2.00–2.11 Å. Hf is bonded in a 4-coordinate geometry to four equivalent O atoms. All Hf–O bond lengths are 2.13 Å. B is bonded in a single-bond geometry to one O atom. The B–O bond length is 1.46 Å. There are five inequivalent O sites. In the first O site, O is bonded to five Mg and one B atom to form distorted OMg5B octahedra that share corners with four equivalent OMg5B octahedra, a cornercorner with one OMg5 trigonal bipyramid, and edges with four equivalent OMg5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 6°. In the second O site, O is bonded to five Mg atoms to form distorted OMg5 trigonal bipyramids that share a cornercorner with one OMg5B octahedra, corners with eight OMg5 trigonal bipyramids, and edges with four equivalent OMg5 square pyramids. The corner-sharing octahedral tilt angles are 0°. In the third O site, O is bonded to five Mg atoms to form a mixture of distorted edge and corner-sharing OMg5 square pyramids. In the fourth O site, O is bonded in a distorted trigonal non-coplanar geometry to one Mg and two equivalent Hf atoms. In the fifth O site, O is bonded to five Mg atoms to form distorted OMg5 trigonal bipyramids that share corners with two equivalent OMg5 square pyramids, corners with six OMg5 trigonal bipyramids, edges with two equivalent OMg5B octahedra, and edges with four equivalent OMg5 trigonal bipyramids.