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 2.70 Å. There are four inequivalent Mg sites. In the first Mg site, Mg is bonded to five O atoms to form a mixture of edge and corner-sharing MgO5 square pyramids. There are four shorter (2.12 Å) and one longer (2.43 Å) Mg–O bond lengths. In the second Mg site, Mg is bonded to five O atoms to form MgO5 square pyramids that share corners with five MgO5 square pyramids, corners with four equivalent MgO5 trigonal bipyramids, and edges with four equivalent HfO6 octahedra. There are one shorter (2.01 Å) and four longer (2.15 Å) Mg–O bond lengths. In the third Mg site, Mg is bonded in a 2-coordinate geometry to three O atoms. There are two shorter (2.18 Å) and one longer (2.64 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 HfO6 octahedra, corners with two equivalent MgO5 square pyramids, corners with four equivalent MgO5 trigonal bipyramids, edges with two equivalent MgO5 square pyramids, and edges with four equivalent MgO5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 71°. There are a spread of Mg–O bond distances ranging from 1.92–2.24 Å. Hf is bonded to six O atoms to form HfO6 octahedra that share corners with four equivalent HfO6 octahedra, corners with four equivalent MgO5 trigonal bipyramids, and edges with four equivalent MgO5 square pyramids. The corner-sharing octahedral tilt angles are 2°. There are a spread of Hf–O bond distances ranging from 2.03–2.15 Å. 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 corner-sharing OHfMg4 trigonal bipyramids. In the second O site, O is bonded in a 5-coordinate geometry to four equivalent Mg and one Hf atom. 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 a mixture of distorted edge and corner-sharing ORb2Mg3 trigonal bipyramids. In the fifth O site, O is bonded in a 4-coordinate geometry to three Mg and two equivalent Hf atoms.