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6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Y2Si2O7 by Materials Project

Y2Si2O7 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to eight O2- atoms to form distorted YO8 hexagonal bipyramids that share corners with two equivalent SiO4 tetrahedra, edges with two equivalent YO8 hexagonal bipyramids, edges with two equivalent YO6 octahedra, and edges with four SiO4 tetrahedra. There are a spread of Y–O bond distances ranging from 2.33–2.61 Å. In the second Y3+ site, Y3+ is bonded to six O2- atoms to form YO6 octahedra that share corners with two equivalent YO6 octahedra, corners with six SiO4 tetrahedra, and edges with two equivalent YO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 59°. There are four shorter (2.26 Å) and two longer (2.34 Å) Y–O bond lengths. 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 two equivalent YO8 hexagonal bipyramids, corners with two equivalent YO6 octahedra, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent YO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 45°. There is three shorter (1.63 Å) and one longer (1.66 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 YO6 octahedra, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent YO8 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 45–61°. There is three shorter (1.63 Å) and one longer (1.67 Å) Si–O bond length. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Y3+ and two Si4+ atoms. In the second O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Y3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Y3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Y3+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to two Y3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2Si2O7 by Materials Project

Y2Si2O7 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Y3+ is bonded to seven O2- atoms to form distorted YO7 pentagonal bipyramids that share a cornercorner with one YO7 pentagonal bipyramid, corners with four SiO4 tetrahedra, edges with three equivalent YO7 pentagonal bipyramids, and edges with two SiO4 tetrahedra. There are a spread of Y–O bond distances ranging from 2.23–2.50 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 YO7 pentagonal bipyramids, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent YO7 pentagonal bipyramids. There are a spread of Si–O bond distances ranging from 1.62–1.70 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with four equivalent YO7 pentagonal bipyramids, a cornercorner with one SiO4 tetrahedra, and edges with two equivalent YO7 pentagonal bipyramids. There is three shorter (1.63 Å) and one longer (1.69 Å) Si–O bond length. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Y3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Y3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to two equivalent Y3+ and two Si4+ atoms. In the fourth O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Y3+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Y3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2Si2O7 by Materials Project

Y2Si2O7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Y3+ is bonded to six O2- atoms to form distorted YO6 octahedra that share corners with six equivalent SiO4 tetrahedra and edges with three equivalent YO6 octahedra. There are four shorter (2.27 Å) and two longer (2.34 Å) Y–O bond lengths. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six equivalent YO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–57°. There is one shorter (1.64 Å) and three longer (1.65 Å) Si–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Y3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Y3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Y2Si2O7 by Materials Project

Y2Si2O7 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Y3+ is bonded to six O2- atoms to form distorted YO6 octahedra that share corners with six equivalent SiO4 tetrahedra and edges with three equivalent YO6 octahedra. There are a spread of Y–O bond distances ranging from 2.27–2.35 Å. Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with six equivalent YO6 octahedra and a cornercorner with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 42–61°. There are a spread of Si–O bond distances ranging from 1.64–1.66 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Y3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Y3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a linear geometry to two equivalent Si4+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Y3+ and one Si4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Accelerated Design of Cost-Effective Thermal/Environmental Barrier Coatings based on High-Entropy Rare Earth Disilicates: A First-Principles Study

This project aims to design cost-effective thermal/environmental barrier coatings (TEBC) based on high entropy rare earth disilicates to protect SiC-based ceramic matrix composites from chemical and thermal attack for better performance of components in the hot section of gas turbine engines. To accelerate the alloy design, we utilize first-principles density functional theory (DFT) together with combinatorial chemistry methodology to predict key properties including phase stability, apparent bulk coefficient of thermal expansion (ABCTE), intrinsic lattice thermal conductivity, and temperature-dependent elastic constants. Specifically, this project focuses on β-RE2Si2O7 (RE=Yb, Y, Er, Lu, La, Ce,) with β-Yb2Si2O7 and β-Y2Si2O7 as the benchmark. Our DFT calculations predict that Er1/4Lu1/4Y3/4Yb3/4Si2O7 and Er1/2Lu1/2Y1/2Yb1/2Si2O7 have ultralow lattice thermal conductivity < 0.23 W/m/K at 1500 K and a good match of average ABCTE (5.1 - 5.2×10-6 K-1) with SiC. Owing to the low cost and abundant supply of Ce and La, the A- and G-La2Si2O7/Ce2Si2O7 disilicates are also studied. Our study shows that G-phase Ce2Si2O7 has an ultralow thermal conductivity (0.26 W/m/K at 1500 K) and the apparent bulk ABCTE (≈6.9×10-6 K-1) slightly higher than SiC, demonstrating great potential as low-cost high-performance T/EBC. However, La2Si2O7 and Ce2Si2O7 undergo an A-phase to G-phase polymorphic transition at around 1470 K.

environmental barrier coatings↗
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↗