Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Dy2Ti2O7”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Suitability of the rare-earth compounds Dy2Ti2O7 and Gd3Al5O12 for low temperature (4K-20K) magnetic refrigeration cycle

Measurements were made of the magnetic entropy and magnetization of powered samples of the compounds Dy2Ti2O7 and Gd3Al5O12. The magnetization was measured for temperatures at and below 4.2 K, in applied fields ranging to 7.0 tesla. Isothermal changes in magnetic entropy were measured for temperatures from 1.2 to 20 K, in applied fields up to 10 tesla. The results of the measurements are consistent with a doublet ground state for Dy2Ti2O7, and an eight-fold degenerate ground state for Gd3Al5O12. Absolute values of magnetic entropy have been obtained at the lower temperatures, permitting the isotherms to be properly located in the S-H plane with the use of adiabatic magnetization data. The iso-field lines in the S-T plane were determined. The results indicate that Dy2Ti2O7 can absorb a maximum of 71 + or - 4 joules/kg of heat at 4.2 K, while Gd3Al5O12 can absorb 233 + or - joules/kg at the same temperature. The large difference between the two is most likely a result of crystal field interactions in the dysoprosium compound. Both materials can be cycled adiabatically between 4.2 and 20 K.

Flood, D. J.↗
NASA NTRS1974

Magnetization and magnetic entropy of Dy2Ti2O7

Isothermal measurements of the magnetic entropy, magnetization, and differential susceptibility of Dy2Ti2O7 have been made. Absolute values of magnetic entropy have been determined as a function of applied magnetic field for several temperatures in the range 2-20 K, and several isofield lines in the magnetic entropy-temperature plane have been determined. Magnetization measurements, which extended into the saturation region, yield a powder-average magnetic moment of about 4.7 Bohr magnetons per ion. A van Vleck contribution to M was also observed. The results are consistent with the assumption of a nearly pure Jz equals + or - 15/2 ground-state Kramers doublet for the Dy(+++) ion. Comments on the suitability of Dy2Ti2O7 for use in a magnetic refrigerator cycling between 4.2 and 20 K are included.

Flood, D. J.↗
DOE OSTI2020

Materials Data on Dy2Ti2O7 by Materials Project

Dy2Ti2O7 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share edges with six equivalent DyO8 hexagonal bipyramids and edges with six equivalent TiO6 octahedra. There are two shorter (2.20 Å) and six longer (2.49 Å) Dy–O bond lengths. Ti4+ is bonded to six equivalent O2- atoms to form TiO6 octahedra that share corners with six equivalent TiO6 octahedra and edges with six equivalent DyO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 49°. All Ti–O bond lengths are 1.97 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Dy3+ and two equivalent Ti4+ atoms. In the second O2- site, O2- is bonded to four equivalent Dy3+ atoms to form corner-sharing ODy4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy2Ti2O7 by Materials Project

Dy2Ti2O7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are seven inequivalent Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.27–2.88 Å. In the second Dy3+ site, Dy3+ is bonded to six O2- atoms to form distorted DyO6 octahedra that share corners with four equivalent TiO6 octahedra and edges with two equivalent TiO6 octahedra. The corner-sharing octahedral tilt angles are 68°. There are two shorter (2.27 Å) and four longer (2.39 Å) Dy–O bond lengths. In the third Dy3+ site, Dy3+ is bonded to seven O2- atoms to form DyO7 pentagonal bipyramids that share corners with four TiO6 octahedra and edges with two equivalent TiO6 octahedra. The corner-sharing octahedra tilt angles range from 49–66°. There are a spread of Dy–O bond distances ranging from 2.19–2.39 Å. In the fourth Dy3+ site, Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share edges with six DyO8 hexagonal bipyramids and edges with six TiO6 octahedra. There are a spread of Dy–O bond distances ranging from 2.21–2.54 Å. In the fifth Dy3+ site, Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share edges with six DyO8 hexagonal bipyramids and edges with six TiO6 octahedra. There are a spread of Dy–O bond distances ranging from 2.20–2.52 Å. In the sixth Dy3+ site, Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share edges with six DyO8 hexagonal bipyramids and edges with six TiO6 octahedra. There are a spread of Dy–O bond distances ranging from 2.20–2.53 Å. In the seventh Dy3+ site, Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share edges with three DyO8 hexagonal bipyramids and edges with six TiO6 octahedra. There are a spread of Dy–O bond distances ranging from 2.15–2.67 Å. There are eight inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ti–O bond distances ranging from 1.88–2.45 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent DyO6 octahedra, corners with four TiO6 octahedra, and edges with two equivalent DyO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–68°. There are a spread of Ti–O bond distances ranging from 1.91–2.01 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with four equivalent TiO6 octahedra, corners with two equivalent DyO7 pentagonal bipyramids, and edges with two equivalent DyO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There is two shorter (1.92 Å) and four longer (2.03 Å) Ti–O bond length. In the fourth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with five TiO6 octahedra, a cornercorner with one DyO7 pentagonal bipyramid, and edges with four DyO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 47–52°. There are a spread of Ti–O bond distances ranging from 1.89–2.06 Å. In the fifth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with five TiO6 octahedra, a cornercorner with one DyO7 pentagonal bipyramid, and edges with four DyO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 47–52°. There are a spread of Ti–O bond distances ranging from 1.91–2.07 Å. In the sixth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six TiO6 octahedra and edges with six DyO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 49°. There are a spread of Ti–O bond distances ranging from 1.97–1.99 Å. In the seventh Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six TiO6 octahedra and edges with six DyO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 47–52°. There are a spread of Ti–O bond distances ranging from 1.94–2.00 Å. In the eighth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with six TiO6 octahedra and edges with six DyO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 47–49°. There is two shorter (1.96 Å) and four longer (1.98 Å) Ti–O bond length. There are twenty inequivalent O2- sites. In the first O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of edge and corner-sharing ODy3Ti tetrahedra. In the second O2- site, O2- is bonded in a 3-coordinate geometry to one Dy3+ and two equivalent Ti4+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the fifth O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form ODy3Ti tetrahedra that share corners with six ODy3Ti tetrahedra and edges with two ODyTi3 tetrahedra. In the sixth O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of distorted edge and corner-sharing ODy3Ti tetrahedra. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Dy3+ and two equivalent Ti4+ atoms. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the tenth O2- site, O2- is bonded to four Dy3+ atoms to form corner-sharing ODy4 tetrahedra. In the eleventh O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of edge and corner-sharing ODy3Ti tetrahedra. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the thirteenth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Dy3+ and two Ti4+ atoms. In the fourteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the fifteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two equivalent Ti4+ atoms. In the sixteenth O2- site, O2- is bonded to four Dy3+ atoms to form corner-sharing ODy4 tetrahedra. In the seventeenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the eighteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the nineteenth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Dy3+ and two Ti4+ atoms. In the twentieth O2- site, O2- is bonded to one Dy3+ and three Ti4+ atoms to form a mixture of distorted edge and corner-sharing ODyTi3 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy2Ti2O7 by Materials Project

Dy2Ti2O7 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are eight inequivalent Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded to seven O2- atoms to form distorted DyO7 pentagonal bipyramids that share a cornercorner with one DyO7 hexagonal pyramid, a cornercorner with one TiO6 octahedra, a cornercorner with one TiO6 pentagonal pyramid, an edgeedge with one DyO6 octahedra, and an edgeedge with one TiO6 octahedra. The corner-sharing octahedral tilt angles are 74°. There are a spread of Dy–O bond distances ranging from 2.29–2.54 Å. In the second Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.25–2.78 Å. In the third Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to six O2- atoms. There are a spread of Dy–O bond distances ranging from 2.27–2.60 Å. In the fourth Dy3+ site, Dy3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Dy–O bond distances ranging from 2.20–2.53 Å. In the fifth Dy3+ site, Dy3+ is bonded to seven O2- atoms to form distorted DyO7 hexagonal pyramids that share a cornercorner with one DyO7 pentagonal bipyramid, a cornercorner with one TiO6 pentagonal pyramid, an edgeedge with one DyO8 hexagonal bipyramid, an edgeedge with one TiO6 octahedra, and an edgeedge with one TiO6 pentagonal pyramid. There are a spread of Dy–O bond distances ranging from 2.24–2.43 Å. In the sixth Dy3+ site, Dy3+ is bonded to six O2- atoms to form DyO6 octahedra that share corners with four TiO6 octahedra and edges with two equivalent DyO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 56–60°. There are a spread of Dy–O bond distances ranging from 2.19–2.24 Å. In the seventh Dy3+ site, Dy3+ is bonded in a distorted body-centered cubic geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.37–2.71 Å. In the eighth Dy3+ site, Dy3+ is bonded to eight O2- atoms to form distorted DyO8 hexagonal bipyramids that share corners with two equivalent TiO6 octahedra, edges with two equivalent DyO7 hexagonal pyramids, edges with two equivalent TiO6 octahedra, and edges with two equivalent TiO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 57°. There are a spread of Dy–O bond distances ranging from 2.19–2.65 Å. There are eight inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded in a 4-coordinate geometry to five O2- atoms. There are a spread of Ti–O bond distances ranging from 1.78–2.44 Å. In the second Ti4+ site, Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.85–2.38 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent DyO6 octahedra, corners with two equivalent TiO6 octahedra, and edges with two equivalent DyO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 28–60°. There are a spread of Ti–O bond distances ranging from 1.90–2.15 Å. In the fourth Ti4+ site, Ti4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Ti–O bond distances ranging from 1.89–2.11 Å. In the fifth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent DyO6 octahedra, corners with two equivalent TiO6 octahedra, and corners with two equivalent DyO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 28–56°. There are a spread of Ti–O bond distances ranging from 1.90–2.09 Å. In the sixth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with two equivalent TiO6 pentagonal pyramids, and edges with two equivalent DyO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 55°. There are a spread of Ti–O bond distances ranging from 1.89–2.10 Å. In the seventh Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 pentagonal pyramids that share a cornercorner with one DyO7 hexagonal pyramid, corners with two TiO6 octahedra, a cornercorner with one DyO7 pentagonal bipyramid, an edgeedge with one DyO8 hexagonal bipyramid, and an edgeedge with one DyO7 hexagonal pyramid. The corner-sharing octahedra tilt angles range from 24–53°. There are a spread of Ti–O bond distances ranging from 1.87–2.09 Å. In the eighth Ti4+ site, Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with two equivalent DyO8 hexagonal bipyramids, corners with two equivalent TiO6 octahedra, corners with two equivalent TiO6 pentagonal pyramids, and edges with two equivalent DyO7 hexagonal pyramids. The corner-sharing octahedral tilt angles are 55°. There are two shorter (1.96 Å) and four longer (2.08 Å) Ti–O bond lengths. There are twenty-one inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two Dy3+ and one Ti4+ atom. In the second O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Dy3+ and two Ti4+ atoms. In the third O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Dy3+ and two Ti4+ atoms. In the fifth O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form distorted ODy2Ti2 trigonal pyramids that share corners with seven ODy3Ti tetrahedra and a cornercorner with one ODy2Ti2 trigonal pyramid. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Ti4+ atom. In the seventh O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form distorted ODy2Ti2 tetrahedra that share corners with four ODy3Ti tetrahedra, corners with two equivalent ODy2Ti2 trigonal pyramids, and an edgeedge with one ODy3Ti tetrahedra. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Dy3+ and one Ti4+ atom. In the ninth O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form distorted ODy2Ti2 tetrahedra that share corners with five ODy2Ti2 tetrahedra and edges with four ODy3Ti tetrahedra. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the eleventh O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form distorted ODy3Ti tetrahedra that share corners with three ODy2Ti2 tetrahedra, corners with three equivalent ODy2Ti2 trigonal pyramids, and edges with three ODy3Ti tetrahedra. In the twelfth O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of distorted edge and corner-sharing ODy3Ti tetrahedra. In the thirteenth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Dy3+ and two Ti4+ atoms. In the fourteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the fifteenth O2- site, O2- is bonded in a 3-coordinate geometry to two Dy3+ and one Ti4+ atom. In the sixteenth O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form a mixture of distorted edge and corner-sharing ODy2Ti2 tetrahedra. In the seventeenth O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form ODy2Ti2 tetrahedra that share corners with seven ODy3Ti tetrahedra, a cornercorner with one ODy2Ti2 trigonal pyramid, and edges with three ODy2Ti2 tetrahedra. In the eighteenth O2- site, O2- is bonded in a 4-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the nineteenth O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of distorted edge and corner-sharing ODy3Ti tetrahedra. In the twentieth O2- site, O2- is bonded to one Dy3+ and three Ti4+ atoms to form ODyTi3 tetrahedra that share corners with six ODy3Ti tetrahedra and edges with two ODy2Ti2 tetrahedra. In the twenty-first O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form a mixture of distorted edge and corner-sharing ODy3Ti tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Dy2Ti2O7 by Materials Project

Dy2Ti2O7 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent Dy3+ sites. In the first Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.26–2.72 Å. In the second Dy3+ site, Dy3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Dy–O bond distances ranging from 2.23–2.40 Å. In the third Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.24–2.45 Å. In the fourth Dy3+ site, Dy3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Dy–O bond distances ranging from 2.34–2.60 Å. There are four inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 31–46°. There are a spread of Ti–O bond distances ranging from 1.88–2.21 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 26–46°. There are a spread of Ti–O bond distances ranging from 1.83–2.31 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 31–50°. There are a spread of Ti–O bond distances ranging from 1.78–2.28 Å. In the fourth Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted corner-sharing TiO6 octahedra. The corner-sharing octahedra tilt angles range from 26–50°. There are a spread of Ti–O bond distances ranging from 1.83–2.36 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form distorted ODy2Ti2 tetrahedra that share corners with four ODy3Ti tetrahedra and an edgeedge with one ODy2Ti2 tetrahedra. In the second O2- site, O2- is bonded to three Dy3+ and one Ti4+ atom to form distorted corner-sharing ODy3Ti tetrahedra. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Dy3+ and two Ti4+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Dy3+ and two Ti4+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Ti4+ atom. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to three Dy3+ and two equivalent Ti4+ atoms. In the seventh O2- site, O2- is bonded in a 1-coordinate geometry to two Dy3+ and two Ti4+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Dy3+ and one Ti4+ atom. In the ninth O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form a mixture of distorted edge and corner-sharing ODy2Ti2 tetrahedra. In the tenth O2- site, O2- is bonded in a distorted see-saw-like geometry to two Dy3+ and two Ti4+ atoms. In the eleventh O2- site, O2- is bonded to two Dy3+ and two Ti4+ atoms to form a mixture of distorted edge and corner-sharing ODy2Ti2 tetrahedra. In the twelfth O2- site, O2- is bonded in a 4-coordinate geometry to three Dy3+ and one Ti4+ atom. In the thirteenth O2- site, O2- is bonded in a 5-coordinate geometry to three Dy3+ and two equivalent Ti4+ atoms. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Dy3+ and two Ti4+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1973

Magnetic properties of Dy2Ti2O7

Measurements were made of the magnetization, differential magnetic susceptibility, and magnetic entropy of powered samples of Dy2Ti2O7. The saturation magnetic moment is 4.7 + or - 0.2 Bohr magnetons per Dy ion, instead of 10 as predicted by Hund's rules. A temperature-independent magnetization is observed in the saturation region. Absolute values of magnetic entropy have been obtained for temperatures from 1.25 to 20 K, in applied fields up to 10.4 tesla. The magnetic entropy approaches a maximum value consistent with a ground-state multiplicity of 2. Low field magnetization and differential susceptibility data show a transition to antiferromagnetism near 1.35 K. A construction of the magnetic specific heat from the zero field entropy shows an anomaly near the same temperature.

Flood, D. J.↗
DOE OSTI2024

Pyrochlore-type lanthanide titanates and zirconates: Synthesis, structural peculiarities, and properties

This contribution provides a thorough examination of the structural characteristics of pyrochlore-type lanthanide titanates and zirconates Ln2Ti2O7 and Ln2Zr2O7, across various length scales. This paper also examines their processing, interesting physical properties (electrical, magnetic, and thermal characteristics), and responses to high pressure and ion irradiation. Brief sections on the elemental oxides' crystal chemistry, pertinent phase diagrams, and energetics of defect formation are also provided. Pyrochlore-type Ln2Ti2O7 and Ln2Zr2O7 stand out as truly multifunctional materials. Moreover, they have emerged as fascinating materials due to magnetic geometrical frustration, arising from the ordering of magnetic Ln3+ and non-magnetic Ti4+ (or Zr4+) cations into separate, interpenetrating lattices of corner-sharing tetrahedra. This results in a diverse array of exotic magnetic ground states, such as spin-ice (e.g., Dy2Ti2O7 or Ho2Ti2O7) or quantum spin ice (e.g., Tb2Ti2O7), observed at both low and room temperatures. They also exhibit varied electrical and electrochemical characteristics. Some members such as Gd2Zr2O7, function as fast ion conductors with a conductivity (σ) of ≈10−2 S·cm−1 at 800 °C and activation energy (Ea) ranging from 0.85 to 1.52 eV, depending on the degree of structural disorder. Others, such as Gd2TiMoO7, are mixed ionic-electronic conductors with σ ≈ 25 S·cm−1 at 1000 °C, making them promising candidate materials for applications in energy conversion and storage devices and oxygen separation membranes. Their exceptionally low thermal conductivity (e.g., κ ∼ 1.1–1.7 W·m−1·K−1 between 700 and 1200 °C for Ln2Zr2O7), close to the glass-like lower limit of highly disordered solids, positions them as valuable materials for thermal barrier coatings. They can also effectively accommodate actinides (e.g., Pu, Np, Cm, Am) in solid solutions and sustain prolonged exposure to radiation due to alpha-decay events, while preserving the integrity of the periodic atomic structure. Proposed as major components in actinide-bearing ceramics, they contribute to the long-term immobilization and disposal of long-lived waste radionuclides from nuclear programs. Some of these properties are displayed simultaneously, opening avenues for new applications. Despite the wealth of data available in the literature, this review highlights the need for a better understanding of order/disorder processes in pyrochlore-type materials and the influence of the structural length scale on their physical and chemical properties. Recent experimental evidence has revealed that pyrochlore short-range structure is far more complex than originally thought. Moreover, pyrochlore local structure is now believed to include short-range, lower symmetry, ordered domains, such as the orthorhombic weberite-type of structure. Notably, short- and long-range structures appear decoupled across different length scales and temperature regimes, and these differences persist even in well-ordered samples. We believe that the pyrochlore structure offers a unique opportunity for examining the interplay between chemical composition, defect chemistry, and properties. In Memoriam: Rodney C. Ewing, Fondly Remembered.

Physics↗
DOE OSTI2022

Machine Learning assisted optimization and parameter space exploration dataset of spin ice Hamiltonian

This repository contains both simulated and experimental structure factor data for the data challenge involving the inverse scattering problem. The simulated data were generated during a machine-learning-assisted optimization routine described in ref[1]. The experimental structure factor was measured on a rare-earth oxide, Dy2Ti2O7 using diffuse neutron scattering from time-of-flight techniques on the CORELLI instrument at the Spallation Neutron Source, Oak Ridge National Laboratory. A Metropolis Monte Carlo code implemented to run in a High-performance computing setting was used to calculated simulated structure factors for the spin-ice Hamiltonian at 680 mK, which is the same temperature as for the experimental data. The total size of all the files in this repository is 5.12 GB. A detailed description of the files is given below. ExperimentalData_630mK.dat – A linearized version of 3-dimensional experimental data of size 61×81×21. This data was processed to remove an estimation of non-magnetic background, including nuclear scattering signal and instrumentation background. Parameters.dat – 6700 samples were evaluated over the 4-dimensional parameter space (J_1, J_2, J_3 and J_(3^' )). There is an additional parameter, D in the spin Hamiltonian to mimic the dipolar interaction between magnetic ions. However, this parameter, D was fixed to a value determined by prior work. This file contains five columns for the parameters J_1, J_2, J_3, J_(3^' ) and D respectively. 3D_Simulation_Data.dat – The simulated structure factor, S(Q) data are included in this file. Each raw contains a linearized array of 3D volumes of S(Q) calculated for the parameter set given in the corresponding row of the file Parameters.dat. The size of the volume data was matched to the experimental data. Qx(h,-h,0).dat, Qy(k,k,-2k).dat, Qz(l,l,l).dat – These files contain the h, k, and l values along with the reciprocal vectors [h,-h,0], [k,k,-2k] and [l,l,l] respectively.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Technique for direct measurement of magnetic entropy of solids: Results for dysprosium titanium oxide

A measurement technique was devised which permits direct observation of the magnetic entropy of solids as a function of applied magnetic field. Measurements were made of the magnetic entropy, in the temperature range 2 to 20 K, of polycrystalline samples of dysprosium titanium oxide (Dy2Ti2O7) to determine its suitability for use as the working substance of a magnetic refrigerator. Magnetization measurements were also made at 4.2 K and below to provide additional information on the nature of the compound. The measurements indicated that crystalline electric fields perturbed the ground state of the dysprosium ions, removed the 16-fold degeneracy predicted by Hund's rules, and left only a twofold degeneracy in its place. A positive, temperature independent contribution to the magnetization was observed in the saturation region, which indicated that the doublet ground-state wave function was perturbed by a nearby unpopulated upper energy level.

Flood, D. J.↗