Materials Data on RbHfMg6O7 by Materials Project

Abstract

RbMg6HfO7 crystallizes in the tetragonal P4mm space group. The structure is two-dimensional and consists of one RbMg6HfO7 sheet oriented in the (0, 0, 1) direction. Rb is bonded in a 4-coordinate geometry to four equivalent O atoms. All Rb–O bond lengths are 2.71 Å. There are four inequivalent Mg sites. In the first Mg site, Mg is bonded to five O atoms to form MgO5 square pyramids that share a cornercorner with one MgO6 octahedra and corners with four equivalent MgO5 square pyramids. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.12 Å) and one longer (2.51 Å) Mg–O bond lengths. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four equivalent MgO6 octahedra, a cornercorner with one MgO5 square pyramid, and edges with four equivalent HfO5 square pyramids. The corner-sharing octahedral tilt angles are 6°. There are a spread of Mg–O bond distances ranging from 2.12–2.16 Å. In the third Mg site, Mg is bonded in a distorted T-shaped geometry to three O atoms. There are two shorter (2.14 Å) and one longer (2.42 Å) Mg–O bond lengths. In the fourth Mg site, Mg is bonded in a 5-coordinate geometry to five O atoms. There are a spread of Mg–O bond distances ranging from 1.91–2.21 Å. Hf is bonded to five O atoms to form HfO5 square pyramids that share corners with four equivalent HfO5 square pyramids and edges with four equivalent MgO6 octahedra. There are one shorter (1.97 Å) and four longer (2.12 Å) Hf–O bond lengths. There are five inequivalent O sites. In the first O site, O is bonded to four equivalent Mg and one Hf atom to form distorted OHfMg4 trigonal bipyramids that share corners with four equivalent OHf2Mg3 square pyramids and corners with eight OHfMg4 trigonal bipyramids. In the second O site, O is bonded to five Mg atoms to form OMg5 square pyramids that share corners with four equivalent OMg5 square pyramids and edges with four equivalent OHf2Mg3 square pyramids. In the third O site, O is bonded in a 6-coordinate geometry to six Mg atoms. In the fourth O site, O is bonded to two equivalent Rb and three Mg atoms to form distorted ORb2Mg3 trigonal bipyramids that share corners with six OHfMg4 trigonal bipyramids and edges with four equivalent ORb2Mg3 trigonal bipyramids. In the fifth O site, O is bonded to three Mg and two equivalent Hf atoms to form distorted OHf2Mg3 square pyramids that share corners with four equivalent OHf2Mg3 square pyramids, corners with two equivalent OHfMg4 trigonal bipyramids, and edges with six OMg5 square pyramids.