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DOE OSTI2020

Materials Data on Gd2Si2O7 by Materials Project

Gd2Si2O7 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Gd3+ is bonded to seven O2- atoms to form distorted GdO7 pentagonal bipyramids that share corners with three equivalent GdO7 pentagonal bipyramids, corners with four SiO4 tetrahedra, edges with two equivalent GdO7 pentagonal bipyramids, and edges with two SiO4 tetrahedra. There are a spread of Gd–O bond distances ranging from 2.27–2.56 Å. There are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent GdO7 pentagonal bipyramids, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent GdO7 pentagonal bipyramids. There is three shorter (1.63 Å) and one longer (1.70 Å) Si–O bond length. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent GdO7 pentagonal bipyramids, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent GdO7 pentagonal bipyramids. There are a spread of Si–O bond distances ranging from 1.62–1.68 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Gd3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Gd3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Gd3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Gd3+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Gd3+ and two Si4+ atoms.

36 MATERIALS SCIENCE↗

NASA NTRS2023

Influence of Cation Species on Thermal Expansion of Y2Si2O7–Gd2Si2O7 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. 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.

rare earth silicates↗

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↗