DOE OSTI2020
Tc2Al2O5 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Tc2+ sites. In the first Tc2+ site, Tc2+ is bonded in a body-centered cubic geometry to eight equivalent O2- atoms. All Tc–O bond lengths are 2.21 Å. In the second Tc2+ site, Tc2+ is bonded in a square co-planar geometry to four equivalent O2- atoms. All Tc–O bond lengths are 2.53 Å. Al3+ is bonded to five O2- atoms to form distorted corner-sharing AlO5 trigonal bipyramids. There is one shorter (1.86 Å) and four longer (1.87 Å) Al–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Tc2+ and two equivalent Al3+ atoms to form distorted OAl2Tc2 tetrahedra that share corners with two equivalent OAl2Tc4 octahedra, corners with ten equivalent OAl2Tc2 tetrahedra, and edges with five equivalent OAl2Tc2 tetrahedra. The corner-sharing octahedral tilt angles are 73°. In the second O2- site, O2- is bonded to four equivalent Tc2+ and two equivalent Al3+ atoms to form distorted OAl2Tc4 octahedra that share corners with four equivalent OAl2Tc4 octahedra, corners with eight equivalent OAl2Tc2 tetrahedra, and edges with four equivalent OAl2Tc4 octahedra. The corner-sharing octahedral tilt angles are 0°.