Materials Data on HfMg6AlO8 by Materials Project

Abstract

MgHfO2Mg5AlO6 crystallizes in the tetragonal P4/mmm space group. The structure is two-dimensional and consists of one Mg5AlO6 sheet oriented in the (0, 0, 1) direction and one MgHfO2 sheet oriented in the (0, 0, 1) direction. In the Mg5AlO6 sheet, there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four equivalent MgO6 octahedra, edges with four equivalent AlO6 octahedra, and edges with eight equivalent MgO5 square pyramids. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.09 Å) and two longer (2.28 Å) Mg–O bond lengths. In the second Mg site, Mg is bonded to five O atoms to form distorted MgO5 square pyramids that share corners with five equivalent MgO5 square pyramids, edges with two equivalent MgO6 octahedra, edges with two equivalent AlO6 octahedra, and edges with four equivalent MgO5 square pyramids. There are a spread of Mg–O bond distances ranging from 2.09–2.29 Å. Al is bonded to six O atoms to form AlO6 octahedra that share corners with four equivalent AlO6 octahedra, edges with four equivalent MgO6 octahedra, and edges with eight equivalent MgO5 square pyramids. The corner-sharing octahedral tilt angles are 0°. There is two shorter (1.83 Å) and four longer (2.09 Å) Al–O bond length. There are three inequivalent O sites. In the first O site, O is bonded to four equivalent Mg and one Al atom to form distorted OMg4Al square pyramids that share corners with five equivalent OMg4Al square pyramids, edges with four equivalent OMg4Al2 octahedra, and edges with four equivalent OMg5 square pyramids. In the second O site, O is bonded to five Mg atoms to form OMg5 square pyramids that share corners with five equivalent OMg5 square pyramids, edges with four equivalent OMg4Al2 octahedra, and edges with four equivalent OMg4Al square pyramids. In the third O site, O is bonded to four Mg and two equivalent Al atoms to form OMg4Al2 octahedra that share corners with four equivalent OMg4Al2 octahedra, edges with four equivalent OMg4Al2 octahedra, and edges with eight OMg4Al square pyramids. The corner-sharing octahedral tilt angles are 0°. In the MgHfO2 sheet, Mg is bonded in a square co-planar geometry to four equivalent O atoms. All Mg–O bond lengths are 2.09 Å. Hf is bonded in a square co-planar geometry to four equivalent O atoms. All Hf–O bond lengths are 2.09 Å. O is bonded in a square co-planar geometry to two equivalent Mg and two equivalent Hf atoms.