Title: Local structure and its implications for the relaxor ferroelectric ${\mathrm{Cd}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$

Abstract

The relaxor ferroelectric transition in Cd₂Nb₂O₇ is thought to be described by the unusual condensation of two Γ-centered phonon modes, $$Γ^–_4$$ and $$Γ^–_5$$. However, their respective roles have proven to be ambiguous, with disagreement between ab initio studies, which favor $$Γ^–_4$$ as the primary mode, and global crystal refinements, which point to $$Γ^–_5$$ instead. Here, we resolve this issue by demonstrating from x-ray pair distribution function measurements that locally, $$Γ^–_4$$ dominates, but globally, $$Γ^–_5$$ dominates. This behavior is consistent with the near degeneracy of the energy surfaces associated with these two distortion modes found in our own ab initio simulations. Our first-principles calculations also show that these energy surfaces are almost isotropic, providing an explanation for the numerous structural transitions found in Cd₂Nb₂O₇, as well as its relaxor behavior. Our results point to several candidate descriptions of the local structure, some of which demonstrate two-in/two-out behavior for Nb displacements within a given Nb tetrahedron. Although this suggests the possibility of a charge analog of spin ice in Cd₂Nb₂O₇, our results are more consistent with a Heisenberg-like description for dipolar fluctuations rather than an Ising one. We hope this encourages future experimental investigations of the Nb and Cd dipolar fluctuations, along with their associated mode dynamics.

Authors:

Hickox-Young, Daniel ;

• Search DOE PAGES for author "Hickox-Young, Daniel"
• Search DOE PAGES for ORCID "0000-0002-5411-0497"

Laurita, Geneva ;

• Search DOE PAGES for author "Laurita, Geneva"
• Search DOE PAGES for ORCID "0000-0001-9577-150X"

Meier, Quintin N. ;

• Search DOE PAGES for author "Meier, Quintin N."
• Search DOE PAGES for ORCID "0000-0001-5881-9551"

Olds, Daniel; Spaldin, Nicola A. ;

• Search DOE PAGES for author "Spaldin, Nicola A."
• Search DOE PAGES for ORCID "0000-0003-0709-9499"

Norman, Michael R. ;

• Search DOE PAGES for author "Norman, Michael R."
• Search DOE PAGES for ORCID "0000-0002-9459-078X"

Rondinelli, James M.

• Search DOE PAGES for author "Rondinelli, James M."
• Search DOE PAGES for ORCID "0000-0003-0508-2175"

Publication Date:

Tue Sep 06 00:00:00 EDT 2022

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States); Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Org.:

National Science Foundation (NSF); Bates College; USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; European Research Council (ERC); European Union (EU); Swiss National Science Foundation (SNF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division

OSTI Identifier:

1885603

Alternate Identifier(s):

OSTI ID: 1905069; OSTI ID: 1922724

Report Number(s):

BNL-223947-2023-JAAM
Journal ID: ISSN 2643-1564; PPRHAI; 033187

Grant/Contract Number:  

SC0012704; AC02-06CH11357; DMR-2011208; DMR-1904980; 810451

Resource Type:

Published Article

Journal Name:

Physical Review Research

Additional Journal Information:

Journal Name: Physical Review Research Journal Volume: 4 Journal Issue: 3; Journal ID: ISSN 2643-1564

Publisher:

American Physical Society

Country of Publication:

United States

Language:

English

Subject:

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; ferroelectricity; pyrochlores; relaxor ferroelectrics; density functional calculations; density functional theory; x-ray pair-distribution function analysis