Department or Program

Chemistry

Abstract

Structural distortions such as cation off-centering are frustrated in the pyrochlore structure due to the triangular arrangement of cations on the lattice. This geometric constraint inhibits a transition from a paraelectric to ferroelectric phase in majority of pyrochlore oxide materials. Few pyrochlore materials can overcome this frustration and exhibit polar crystal structures, and unraveling the origin of such leads to the understanding of polarity in complex materials. Herein we hypothesize that frustration on the pyrochlore lattice can be relieved through doping rare earth cations on the A site which do not possess stereochemically active lone pairs. To assess if frustration is relieved, we have analyzed cation off-centering in various Bi2–xRExTi2O7 (RE = Y, Ho) pyrochlores through neutron total scattering. We present our findings, motivated by known distortions from the pyrochlore literature, that most samples show local distortions similar to the β-cristobalite structure. We additionally comment on the complexity of factors that play a role in the structural behavior, including cation size, bond valence, electronic structure, and magnetic interactions. We posit that the addition of magnetic cations on the lattice may be responsible for an extension of the real-space correlation length in the Bi-Ho series, and offer considerations for driving long-range polarity on the pyrochlore lattice.

Level of Access

Restricted: Embargoed [Open Access After Expiration]

First Advisor

Laurita-Plankis, Geneva

Date of Graduation

5-2022

Degree Name

Bachelor of Science

Number of Pages

55

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Embargoed

Available to all on Tuesday, March 30, 2027

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