Results for “Y2TiO5” | Engineering Papers

DOE OSTI2024

Unveiling and Mapping Polymorphs in Fluorite Y2TiO5 Using 4D-STEM and Unsupervised Machine Learning

Y2TiO5 belongs to the Ln2TiO5 (Ln = lanthanide or Y) family of ceramic materials and exhibits a range of desirable material properties such as radiation tolerance, frustrated magnetism, and large dielectric constant. However, understanding the complex crystal structure of Y2TiO5 remains elusive, given that Y2TiO5 can adopt multiple polymorphs such as cubic, orthorhombic, and hexagonal phases within the lattice. In this work, we report a detailed structural analysis of Y2TiO5 using four-dimensional scanning transmission electron microscopy coupled with unsupervised machine learning. The pyrochlore nanodomains, characterized by the ordered arrangement of yttrium cations on the A site of their A2BO5 structure, are present within the matrix of a predominantly fluorite-structured Y2TiO5 along with a third polymorph, the hexagonal phase. The pyrochlore phase is found to form 2 nm boundary regions around hexagonal phase stacking faults, highlighting the potential influence of the hexagonal phase on the occurrence and distribution of the pyrochlore phase. Lastly, we identify a unique pyrochlore phase with asymmetric arrangement of cation ordering along a single planar direction. Our findings provide invaluable insights into the possible mechanisms stabilizing pyrochlore nanodomains within the fluorite lattice of Y2TiO5.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Y2TiO5 by Materials Project

Y2TiO5 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Y3+ sites. In the first Y3+ site, Y3+ is bonded to seven O2- atoms to form distorted YO7 hexagonal pyramids that share corners with two equivalent YO7 pentagonal bipyramids, a cornercorner with one TiO5 trigonal bipyramid, edges with four equivalent YO7 hexagonal pyramids, edges with three equivalent YO7 pentagonal bipyramids, and edges with two equivalent TiO5 trigonal bipyramids. There are a spread of Y–O bond distances ranging from 2.34–2.37 Å. In the second Y3+ site, Y3+ is bonded to seven O2- atoms to form distorted YO7 pentagonal bipyramids that share corners with two equivalent YO7 hexagonal pyramids, corners with three equivalent TiO5 trigonal bipyramids, edges with three equivalent YO7 hexagonal pyramids, edges with two equivalent YO7 pentagonal bipyramids, and edges with two equivalent TiO5 trigonal bipyramids. There are a spread of Y–O bond distances ranging from 2.29–2.39 Å. Ti4+ is bonded to five O2- atoms to form distorted TiO5 trigonal bipyramids that share a cornercorner with one YO7 hexagonal pyramid, corners with three equivalent YO7 pentagonal bipyramids, corners with two equivalent TiO5 trigonal bipyramids, edges with two equivalent YO7 hexagonal pyramids, and edges with two equivalent YO7 pentagonal bipyramids. There are a spread of Ti–O bond distances ranging from 1.79–1.97 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to two Y3+ and two equivalent Ti4+ atoms to form distorted OY2Ti2 tetrahedra that share corners with six OY2Ti2 tetrahedra and edges with five OY4 tetrahedra. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Y3+ and one Ti4+ atom. In the third O2- site, O2- is bonded to three Y3+ and one Ti4+ atom to form a mixture of edge and corner-sharing OY3Ti tetrahedra. In the fourth O2- site, O2- is bonded to four Y3+ atoms to form OY4 tetrahedra that share corners with fourteen OY2Ti2 tetrahedra and edges with four OY4 tetrahedra. In the fifth O2- site, O2- is bonded to three Y3+ and one Ti4+ atom to form distorted OY3Ti tetrahedra that share corners with nine OY2Ti2 tetrahedra and edges with five OY4 tetrahedra.

36 MATERIALS SCIENCE↗