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DOE OSTI2023

Influence of cation species on thermal expansion of Y 2 Si 2 O 7 –Gd 2 Si 2 O 7 solid solutions

Mixtures of Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 were synthesized by solid-state reaction at 1600°C and characterized via in situ x-ray diffraction (XRD) to determine their coefficients of thermal expansion (CTE). All solid solutions within the system exhibited the orthorhombic δ-RE 2 Si 2 O 7 (Pna2 1 ) structure. Thermal expansion measurements of Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 correlated well with reported values in literature, and all synthesized solid solutions exhibited CTEs between Y 2 Si 2 O 7 and Gd 2 Si 2 O 7 . Generally, there was a slight decrease in CTE exhibited by the materials with increasing Gd 2 Si 2 O 7 content, with Gd 2 Si 2 O 7 having the lowest CTEs and Y 2 Si 2 O 7 the highest CTEs. Here, the decrease in CTE was attributed to stronger bonds of Gd-O over Y-O, as determined by calculated crystal orbital Hamilton populations using density functional theory. However, such differences were very small and crystal structure was the dominating factor in CTE trends.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Materials Data on Gd2O3 by Materials Project

Gd2O3 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Gd3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Gd–O bond distances ranging from 2.25–2.62 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to six equivalent Gd3+ atoms to form OGd6 octahedra that share corners with twelve equivalent OGd4 tetrahedra, edges with six equivalent OGd6 octahedra, and edges with six equivalent OGd4 tetrahedra. In the second O2- site, O2- is bonded to four equivalent Gd3+ atoms to form OGd4 tetrahedra that share corners with six equivalent OGd6 octahedra, corners with six equivalent OGd4 tetrahedra, edges with three equivalent OGd6 octahedra, and edges with three equivalent OGd4 tetrahedra. The corner-sharing octahedra tilt angles range from 18–56°.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on GdO2 by Materials Project

GdO2 crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Gd is bonded in a 9-coordinate geometry to nine O atoms. There are a spread of Gd–O bond distances ranging from 2.38–2.47 Å. There are two inequivalent O sites. In the first O site, O is bonded in a 4-coordinate geometry to four equivalent Gd atoms. In the second O site, O is bonded to five equivalent Gd atoms to form a mixture of distorted edge and corner-sharing OGd5 trigonal bipyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Gd2O3 by Materials Project

Gd2O3 is Corundum-like structured and crystallizes in the cubic I2_13 space group. The structure is three-dimensional. there are three inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded to six O2- atoms to form a mixture of corner and edge-sharing GdO6 octahedra. The corner-sharing octahedra tilt angles range from 56–57°. All Gd–O bond lengths are 2.34 Å. In the second Gd3+ site, Gd3+ is bonded to six O2- atoms to form a mixture of distorted corner and edge-sharing GdO6 octahedra. The corner-sharing octahedra tilt angles range from 54–57°. There are a spread of Gd–O bond distances ranging from 2.30–2.40 Å. In the third Gd3+ site, Gd3+ is bonded to six O2- atoms to form a mixture of distorted corner and edge-sharing GdO6 octahedra. The corner-sharing octahedra tilt angles range from 55–56°. There are a spread of Gd–O bond distances ranging from 2.30–2.40 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four Gd3+ atoms to form a mixture of distorted corner and edge-sharing OGd4 trigonal pyramids. In the second O2- site, O2- is bonded to four Gd3+ atoms to form a mixture of distorted corner and edge-sharing OGd4 trigonal pyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Gd2O3 by Materials Project

Gd2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Gd3+ sites. In the first Gd3+ site, Gd3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing GdO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Gd–O bond distances ranging from 2.26–2.52 Å. In the second Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Gd–O bond distances ranging from 2.29–2.81 Å. In the third Gd3+ site, Gd3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Gd–O bond distances ranging from 2.28–2.69 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to five Gd3+ atoms to form distorted OGd5 trigonal bipyramids that share corners with seven OGd4 tetrahedra, corners with two equivalent OGd4 trigonal pyramids, edges with two equivalent OGd6 octahedra, edges with three OGd4 tetrahedra, edges with two equivalent OGd5 trigonal bipyramids, and edges with three equivalent OGd4 trigonal pyramids. In the second O2- site, O2- is bonded to four Gd3+ atoms to form OGd4 tetrahedra that share a cornercorner with one OGd6 octahedra, corners with four OGd4 tetrahedra, corners with five equivalent OGd5 trigonal bipyramids, corners with three equivalent OGd4 trigonal pyramids, edges with two equivalent OGd6 octahedra, edges with two equivalent OGd4 tetrahedra, and an edgeedge with one OGd5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 49°. In the third O2- site, O2- is bonded to four Gd3+ atoms to form distorted OGd4 tetrahedra that share corners with two equivalent OGd6 octahedra, corners with four OGd4 tetrahedra, corners with two equivalent OGd5 trigonal bipyramids, corners with six equivalent OGd4 trigonal pyramids, an edgeedge with one OGd6 octahedra, an edgeedge with one OGd4 tetrahedra, and edges with two equivalent OGd5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 12°. In the fourth O2- site, O2- is bonded to four Gd3+ atoms to form distorted OGd4 trigonal pyramids that share a cornercorner with one OGd6 octahedra, corners with nine OGd4 tetrahedra, corners with two equivalent OGd5 trigonal bipyramids, corners with two equivalent OGd4 trigonal pyramids, edges with three equivalent OGd5 trigonal bipyramids, and edges with two equivalent OGd4 trigonal pyramids. The corner-sharing octahedral tilt angles are 37°. In the fifth O2- site, O2- is bonded to six Gd3+ atoms to form OGd6 octahedra that share corners with six OGd4 tetrahedra, corners with two equivalent OGd4 trigonal pyramids, edges with two equivalent OGd6 octahedra, edges with six OGd4 tetrahedra, and edges with four equivalent OGd5 trigonal bipyramids.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Gd2O3 by Materials Project

Gd2O3 crystallizes in the cubic Pn-3m space group. The structure is three-dimensional. Gd3+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. All Gd–O bond lengths are 2.32 Å. O2- is bonded to four equivalent Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on GdO by Materials Project

GdO is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Gd is bonded to four equivalent O atoms to form corner-sharing GdO4 tetrahedra. All Gd–O bond lengths are 2.33 Å. O is bonded to four equivalent Gd atoms to form corner-sharing OGd4 tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on GdO3 by Materials Project

GdO3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Gd is bonded in a 9-coordinate geometry to nine equivalent O atoms. There are three shorter (2.36 Å) and six longer (2.37 Å) Gd–O bond lengths. O is bonded in a trigonal non-coplanar geometry to three equivalent Gd atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Gd2O3 by Materials Project

Gd2O3 crystallizes in the tetragonal P-4m2 space group. The structure is three-dimensional. Gd3+ is bonded in a 6-coordinate geometry to six O2- atoms. There are four shorter (2.27 Å) and two longer (2.50 Å) Gd–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 tetrahedra. In the second O2- site, O2- is bonded to four equivalent Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 tetrahedra. In the third O2- site, O2- is bonded to four equivalent Gd3+ atoms to form a mixture of edge and corner-sharing OGd4 tetrahedra.

36 MATERIALS SCIENCE↗