DOE OSTI2020
HfRhAl crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are two inequivalent Hf sites. In the first Hf site, Hf is bonded in a 12-coordinate geometry to three equivalent Hf, five Rh, and four equivalent Al atoms. All Hf–Hf bond lengths are 3.20 Å. There are a spread of Hf–Rh bond distances ranging from 2.82–3.19 Å. There are two shorter (3.16 Å) and two longer (3.17 Å) Hf–Al bond lengths. In the second Hf site, Hf is bonded in a 7-coordinate geometry to four Hf, seven Rh, and five Al atoms. The Hf–Hf bond length is 2.95 Å. There are a spread of Hf–Rh bond distances ranging from 3.01–3.06 Å. There are three shorter (3.03 Å) and two longer (3.16 Å) Hf–Al bond lengths. There are three inequivalent Rh sites. In the first Rh site, Rh is bonded to six Hf and six Al atoms to form a mixture of distorted corner and edge-sharing RhHf6Al6 cuboctahedra. There are a spread of Rh–Al bond distances ranging from 2.57–2.73 Å. In the second Rh site, Rh is bonded in a 12-coordinate geometry to six Hf, four Rh, and two equivalent Al atoms. There are a spread of Rh–Rh bond distances ranging from 2.63–2.72 Å. Both Rh–Al bond lengths are 2.53 Å. In the third Rh site, Rh is bonded in a 12-coordinate geometry to six Hf, four equivalent Rh, and two equivalent Al atoms. Both Rh–Al bond lengths are 2.54 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 12-coordinate geometry to three equivalent Hf, four Rh, and two equivalent Al atoms. Both Al–Al bond lengths are 2.65 Å. In the second Al site, Al is bonded in a 12-coordinate geometry to six Hf, two equivalent Rh, and four Al atoms. There are one shorter (2.59 Å) and one longer (2.76 Å) Al–Al bond lengths.