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DOE OSTI2020

Materials Data on ZrTiO4 by Materials Project

ZrTiO4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to six O2- atoms to form distorted ZrO6 octahedra that share corners with eight TiO6 octahedra and an edgeedge with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 46–60°. There are a spread of Zr–O bond distances ranging from 2.05–2.31 Å. In the second Zr4+ site, Zr4+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Zr–O bond distances ranging from 2.05–2.31 Å. In the third Zr4+ site, Zr4+ is bonded to six O2- atoms to form distorted ZrO6 octahedra that share corners with four equivalent ZrO6 octahedra, corners with four TiO6 octahedra, and an edgeedge with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 49–62°. There are a spread of Zr–O bond distances ranging from 2.06–2.22 Å. In the fourth Zr4+ site, Zr4+ is bonded to six O2- atoms to form distorted ZrO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four equivalent ZrO6 octahedra, and edges with two TiO6 octahedra. The corner-sharing octahedra tilt angles range from 54–62°. There are a spread of Zr–O bond distances ranging from 2.04–2.23 Å. There are four inequivalent Ti4+ sites. In the first Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with two equivalent ZrO6 octahedra, corners with six TiO6 octahedra, and edges with two ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 47–55°. There are a spread of Ti–O bond distances ranging from 1.88–2.27 Å. In the second Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with two equivalent TiO6 octahedra, corners with four equivalent ZrO6 octahedra, and edges with two TiO6 octahedra. The corner-sharing octahedra tilt angles range from 46–60°. There are a spread of Ti–O bond distances ranging from 1.89–2.16 Å. In the third Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with four ZrO6 octahedra, an edgeedge with one ZrO6 octahedra, and an edgeedge with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Ti–O bond distances ranging from 1.88–2.16 Å. In the fourth Ti4+ site, Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with four ZrO6 octahedra, corners with four equivalent TiO6 octahedra, an edgeedge with one ZrO6 octahedra, and an edgeedge with one TiO6 octahedra. The corner-sharing octahedra tilt angles range from 47–56°. There are a spread of Ti–O bond distances ranging from 1.86–2.25 Å. There are sixteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Zr4+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the seventh O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the ninth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the tenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to three Ti4+ atoms. In the twelfth O2- site, O2- is bonded in a trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the thirteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the fourteenth O2- site, O2- is bonded in a trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the fifteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Zr4+ and one Ti4+ atom. In the sixteenth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two Ti4+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on ZrTiO4 by Materials Project

ZrTiO4 is zeta iron carbide-derived structured and crystallizes in the orthorhombic P2_12_12 space group. The structure is three-dimensional. Zr4+ is bonded to six O2- atoms to form distorted ZrO6 octahedra that share corners with four equivalent ZrO6 octahedra, corners with four equivalent TiO6 octahedra, and edges with two equivalent TiO6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Zr–O bond distances ranging from 2.05–2.25 Å. Ti4+ is bonded to six O2- atoms to form distorted TiO6 octahedra that share corners with four equivalent ZrO6 octahedra, corners with four equivalent TiO6 octahedra, and edges with two equivalent ZrO6 octahedra. The corner-sharing octahedra tilt angles range from 48–55°. There are a spread of Ti–O bond distances ranging from 1.90–2.09 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Zr4+ and one Ti4+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to one Zr4+ and two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗

NASA NTRS2004

Increasing the Thermal Stability of Aluminum Titanate for Solid Oxide Fuel Cell Anodes

Solid-oxide fuel cells (SOFCs) show great potential as a power source for future space exploration missions. Because SOFCs operate at temperatures significantly higher than other types of fuel cells, they can reach overall efficiencies of up to 60% and are able to utilize fossil fuels. The SOFC team at GRC is leading NASA's effort to develop a solid oxide fuel cell with a power density high enough to be used for aeronautics and space applications, which is approximately ten times higher than ground transport targets. layers must be able to operate as a single unit at temperatures upwards of 900'C for at least 40,000 hours with less than ten percent degradation. One key challenge to meeting this goal arises from the thermal expansion mismatch between different layers. The amount a material expands upon heating is expressed by its coefficient of thermal expansion (CTE). If the CTEs of adjacent layers are substantially different, thermal stresses will arise during the cell's fabrication and operation. These stresses, accompanied by thermal cycling, can fracture and destroy the cell. While this is not an issue at the electrolyte-cathode interface, it is a major concern at the electrolyte-anode interface, especially in high power anode-supported systems. electrolyte are nearly identical. Conventionally, this has been accomplished by varying the composition of the anode to match the CTE of the yittria-stabilized zirconia (YSZ) electrolyte (approx.10.8x10(exp -6/degC). A Ni/YSZ composite is typically used as a base material for the anode due to its excellent electrochemical properties, but its CTE is about 13.4x10(exp -6/degC). One potential way to lower the CTE of this anode is to add a small percentage of polycrystalline Al2TiO5, with a CTE of 0.68x10(exp -6/degC, to the Ni/YSZ base. However, Al2TiO5 is thermally unstable and loses its effectiveness as it decomposes to Al2O3 and TiO2 between 750 C and 1280 C. be used as additives to increase the thermal stability of Al2TiO5 in SOFC operating conditions without adversely affecting the electrochemical properties of the SOFC anode. Three candidate materials were chosen through an extensive literature review: MgO, Fe2O3, and ZrTiO4. Although all three have been shown to prevent Al2TiO5 decomposition under various conditions, their effectiveness in the temperature range and atmosphere of the SOFC has not yet been evaluated. Several batches of Al2TiO5 with varying amounts of additives were prepared, exposed to reducing and oxidizing atmospheres at elevated temperatures, and the resulting decomposition of Al2TiO5 was measured. The most promising additives were further evaluated with the goal of ultimately preparing low CTE anodes that are chemically compatible to current systems. Adding minor constituents to stabilize Al2TiO5 could ultimately preserve its low CTE for the life of the fuel cell and improve the cell's long-term performance without a drop in anode conductivity. Further, these low CTE filler additions could allow the use of new sulfur tolerant anode materials, improving the viability of SOFCs for future aeronautics and space applications. Every SOFC consists of a cathode and an anode separated by an electrolyte, These three One way to avoid this problem is to design the cell such that the CTEs of the anode and The objective of this summer research project was to evaluate several materials that could

Bender, Jeffrey B.↗