Geneva Laurita-Plankis, Bates College

Polar materials play a large role in the electronics industry, but many of the leading materials rely on the chemistry of lead for enhanced performance. Several types of materials have been explored in an effort to find lead-free alternatives for use in electronic devices, but there are still many challenges to replacing lead. One type of material that has been relatively unexplored for these applications is the pyrochlore family of crystalline materials, with the chemical formula A2B2O7. The triangular arrangement of cations on the pyrochlore lattice leads to frustration of electronic dipoles, which prevents the formation of a long-range polar materials. However, several pyrochlore materials overcome this frustration and exhibit polar crystal structures, and unraveling the origin of such leads to the understanding of polarity in complex materials. Herein I will discuss variations in local distortions and crystallographic polarity in niobate and titanate pyrochlores with chemical substitution on various sites of the A2B2O6O’ pyrochlore structure: namely, A-site cations with an s2 lone pair of electrons, and anions with varying electronegativity on the O’ site. Analysis of neutron and X-ray scattering data reveals local dipoles are induced with lone pair-bearing cations, and changes in polar distortions of the pyrochlore lattice accompany varying anion composition. This work informs on the interactions between the networks in the pyrochlore structure, and suggests routes for manipulating polar behavior in pyrochlores towards the design of new materials for electronic applications.