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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LaOF by Materials Project

LaOF is half-Heusler structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. La3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All La–O bond lengths are 2.50 Å. All La–F bond lengths are 2.50 Å. O2- is bonded to four equivalent La3+ atoms to form OLa4 tetrahedra that share corners with four equivalent FLa4 tetrahedra, corners with twelve equivalent OLa4 tetrahedra, and edges with six equivalent FLa4 tetrahedra. F1- is bonded to four equivalent La3+ atoms to form FLa4 tetrahedra that share corners with four equivalent OLa4 tetrahedra, corners with twelve equivalent FLa4 tetrahedra, and edges with six equivalent OLa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaOF by Materials Project

LaOF crystallizes in the trigonal R-3m space group. The structure is three-dimensional. La3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. There are one shorter (2.40 Å) and three longer (2.43 Å) La–O bond lengths. There are three shorter (2.59 Å) and one longer (2.65 Å) La–F bond lengths. O2- is bonded to four equivalent La3+ atoms to form OLa4 tetrahedra that share corners with six equivalent OLa4 tetrahedra, corners with ten equivalent FLa4 tetrahedra, edges with three equivalent OLa4 tetrahedra, and edges with three equivalent FLa4 tetrahedra. F1- is bonded to four equivalent La3+ atoms to form distorted FLa4 tetrahedra that share corners with six equivalent FLa4 tetrahedra, corners with ten equivalent OLa4 tetrahedra, edges with three equivalent OLa4 tetrahedra, and edges with three equivalent FLa4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaOF by Materials Project

LaOF crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. La3+ is bonded in a body-centered cubic geometry to four equivalent O2- and four equivalent F1- atoms. All La–O bond lengths are 2.40 Å. All La–F bond lengths are 2.64 Å. O2- is bonded to four equivalent La3+ atoms to form distorted OLa4 tetrahedra that share corners with four equivalent OLa4 tetrahedra, corners with twelve equivalent FLa4 tetrahedra, edges with two equivalent FLa4 tetrahedra, and edges with four equivalent OLa4 tetrahedra. F1- is bonded to four equivalent La3+ atoms to form distorted FLa4 tetrahedra that share corners with four equivalent FLa4 tetrahedra, corners with twelve equivalent OLa4 tetrahedra, edges with two equivalent OLa4 tetrahedra, and edges with four equivalent FLa4 tetrahedra.

36 MATERIALS SCIENCE↗
NASA NTRS2020

Thermal Analysis, Compressibility, and Decomposition of Synthetic Bastnäsite-(La) to Lanthanum Oxyfluoride

Understanding basic material properties of rare earth element (REE) bearing minerals such as their phase stability and equations of state can assist in understanding how economically viable deposits might form. Bastnäsite is the most commonly mined REE bearing mineral. We synthesized the lanthanum-fluoride end member, bastnäsite-(La) (LaCO3F), and investigated its thermal behavior and decomposition products from 298 K to 1173 K under ambient pressure conditions through thermogravimetric analysis, differential scanning calorimetry, evolved gas analysis, and high temperature powder X-ray diffraction. We also investigated the compressibility of bastnäsite-(La) via single crystal X-ray diffraction in diamond anvil cells at an ambient temperature up to 11.3 GPa and from 4.9 GPa to 7.7 GPa up to 673 K. At ambient pressure, bastnäsite-(La) was stable up to 598 K in air, where it decomposed into CO2 and tetragonal γ-LaOF. Above 948 K, cubic α-LaOF is stable. High temperature X-ray diffraction data were used to fit the Fei thermal equation of state and the thermal expansion coefficient α(sub 298) for all three materials. Bastnäsite-(La) was fit from 298 K to 723 K with V(sub 0) = 439.82 Å(exp 3), α(sub 298) = 4.32 × 10(exp -5) K(exp -1), a(sub 0) = −1.68 × 10(exp -5) K(exp -1), a(sub 1) = 8.34 × 10(exp -8) K(exp -1), and a(sub 2) = 3.126 K(exp -1). Tetragonal γ-LaOF was fit from 723 K to 948 K with V(sub 0) = 96.51 Å(exp 3), α(sub 298) = 2.95×10(exp -4) K(exp -1), a(sub 0) = −2.41×10(exp -5) K(exp -1), a(sub 1) = 2.42×10(exp -7) K(exp -1), and a(sub 2) = 41.147 K(exp -1). Cubic α-LaOF was fit from 973 K to 1123 K with V(sub 0) = 190.71 Å(exp 3), α(sub 298) = −1.12×10(exp -5) K(exp -1), a(sub 0) = 2.36×10(exp -4) K(exp -1), a(sub 1) = −1.73 × 10(exp -7) K(exp -1), and a(sub 2) = −17.362 K(exp -1). An ambient temperature third order Birch–Murnaghan equation of state was fit with V(sub 0) = 439.82 Å(exp 3), K(sub 0) = 105 GPa, and K’ = 5.58.

Bastnäsite↗