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DOE OSTI2020

Materials Data on Ho2O3 by Materials Project

Ho2O3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ho3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ho–O bond distances ranging from 2.20–2.57 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ho3+ atoms to form OHo4 tetrahedra that share corners with six equivalent OHo6 octahedra, corners with six equivalent OHo4 tetrahedra, edges with three equivalent OHo6 octahedra, and edges with three equivalent OHo4 tetrahedra. The corner-sharing octahedra tilt angles range from 19–55°. In the second O2- site, O2- is bonded to six equivalent Ho3+ atoms to form OHo6 octahedra that share corners with twelve equivalent OHo4 tetrahedra, edges with six equivalent OHo6 octahedra, and edges with six equivalent OHo4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ho2O3 by Materials Project

Ho2O3 crystallizes in the cubic Pn-3m space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. All Ho–O bond lengths are 2.08 Å. O2- is bonded to four equivalent Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Ho2O3 by Materials Project

Ho2O3 crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. Ho3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are four shorter (2.21 Å) and two longer (2.47 Å) Ho–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra. In the second O2- site, O2- is bonded to four equivalent Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra. In the third O2- site, O2- is bonded to four equivalent Ho3+ atoms to form a mixture of edge and corner-sharing OHo4 tetrahedra.

36 MATERIALS SCIENCE↗

NASA NTRS1985

Structure-property relations in lanthanide borate glasses

Glass formation in the system Ln2O3-B2O3 (Ln = Nd, Sm) was studied. Glasses could be formed in the range from 0 to 28 mol pct rare-earth oxide (Ln2O3), but liquid immiscibility in these systems limits the range of homogeneous glasses to 0 to 1.5 and 25 to 28 mol pct Ln2O3. The infrared spectra indicate that the rare-earth-rich glasses are structurally similar to rare-earth metaborates (LnB3O6) which contain (B3O6)-infinity chains. The variation in density, transformation temperature, thermal expansion coefficient, and transformation-range viscosity of these glasses with the size of the rare-earth ion is discussed. Glasses near the metaborate composition have a transformation temperature of about 700 C, which is high for binary borate glasses. Glasses could not be formed in the systems Eu2O3-, Gd2O3-, Ho2O3-, and Er2O3-B2O3, even by quenching at 1300 C/s. The sudden lack of glass formation in the system Ln2O3-B2O3 with Ln(3+) ions smaller than Sm(3+) is explained on the basis of the size effect of the Ln(3+) ion on the stability of (B3O6)-infinity chains in these metaborates.

Chakraborty, I. N.↗

NASA NTRS1989

Thermodynamic properties of some metal oxide-zirconia systems

Metal oxide-zirconia systems are a potential class of materials for use as structural materials at temperatures above 1900 K. These materials must have no destructive phase changes and low vapor pressures. Both alkaline earth oxide (MgO, CaO, SrO, and BaO)-zirconia and some rare earth oxide (Y2O3, Sc2O3, La2O3, CeO2, Sm2O3, Gd2O3, Yb2O3, Dy2O3, Ho2O3, and Er2O3)-zirconia system are examined. For each system, the phase diagram is discussed and the vapor pressure for each vapor species is calculated via a free energy minimization procedure. The available thermodynamic literature on each system is also surveyed. Some of the systems look promising for high temperature structural materials.

Jacobson, Nathan S.↗