Abstract
The study of insulator-to-metal transitions is of interest from the viewpoint of fundamental understanding of the underlying physics, and materials at the brink of such transitions possess useful functionality. Driving this transition through compositional tuning can help engineer useful material properties. Here we study the role of disorder in the form of cation off-centering on the compositionally-controlled insulator-to-metal transition in the solid solution oxide pyrochlore (Pr1-xBix)2Ru2O7. Prior work has established site disorder by the Bi3+ cations shifting incoherently away from their ideal crystallographic site in the Bi end-member pyrochlore as a consequence of stereochemical activity of the lone pair of electrons. However, less is known about the consequences of such off-centering in solid solutions and its role in determining the electronic ground state. Here we demonstrate through total scattering studies that even a small substitution of Bi on the pyrochlore A site leads to site disorder that enhances the average effective size of the A-site cation. This indirectly increases Ru-O-Ru covalency, which appears to play a crucial role in the crossover from insulating to metallic behavior in the solid solution. Further, density functional electronic structure calculations suggest the combination of primary and secondary (due to size) electronic effects of the lone pair-driven incoherent cation displacements drive the solid solution into a metallic state.
| Original language | English (US) |
|---|---|
| Article number | 095003 |
| Journal | Physical Review Materials |
| Volume | 3 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 17 2019 |
Funding
G.L. gratefully acknowledges support for this work from Bates College and from the National Science Foundation (NSF) through DMR 1904980. The work at Northwestern and at UC Santa Barbara was supported by NSF DMR 1729303. The computational contributions of D.P. were supported by the Army Research Office under W911NF-15-1-0017. The use of DOD-HPCMP resources for the computational work reported here is gratefully acknowledged. M.W.G. thanks the Leverhulme Trust for funding via the Leverhulme Research Centre for Functional Materials Design. This work was performed, in part, at the Los Alamos Neutron Science Center (LANSCE), a NNSA User Facility operated for the U.S. Department of Energy (DOE) by Los Alamos National Laboratory (Contract 89233218CNA000001). We thank J. Siewenie for assistance with NPDF data collection. G.L. gratefully acknowledges support for this work from Bates College and from the National Science Foundation (NSF) through DMR 1904980. The work at Northwestern and at UC Santa Barbara was supported by NSF DMR 1729303. The computational contributions of D.P. were supported by the Army Research Office under W911NF-15-1-0017. The use of DOD-HPCMP resources for the computational work reported here is gratefully acknowledged. M.W.G. thanks the Leverhulme Trust for funding via the Leverhulme Research Centre for Functional Materials Design. This work was performed, in part, at the Los Alamos Neutron Science Center (LANSCE), a NNSA User Facility operated for the U.S. Department of Energy (DOE) by Los Alamos National Laboratory (Contract 89233218CNA000001). We thank J. Siewenie for assistance with NPDF data collection.
ASJC Scopus subject areas
- General Materials Science
- Physics and Astronomy (miscellaneous)