Abstract
It is shown that structural disorder—in the form of anisotropic, picoscale atomic displacements—modulates the refractive index tensor and results in the giant optical anisotropy observed in BaTiS3, a quasi-1D hexagonal chalcogenide. Single-crystal X-ray diffraction studies reveal the presence of antipolar displacements of Ti atoms within adjacent TiS6 chains along the c-axis, and threefold degenerate Ti displacements in the a–b plane. 47/49Ti solid-state NMR provides additional evidence for those Ti displacements in the form of a three-horned NMR lineshape resulting from a low symmetry local environment around Ti atoms. Scanning transmission electron microscopy is used to directly observe the globally disordered Ti a–b plane displacements and find them to be ordered locally over a few unit cells. First-principles calculations show that the Ti a–b plane displacements selectively reduce the refractive index along the ab-plane, while having minimal impact on the refractive index along the chain direction, thus resulting in a giant enhancement in the optical anisotropy. By showing a strong connection between structural disorder with picoscale displacements and the optical response in BaTiS3, this study opens a pathway for designing optical materials with high refractive index and functionalities such as large optical anisotropy and nonlinearity.
| Original language | English |
|---|---|
| Article number | 2311559 |
| Journal | Advanced Materials |
| Volume | 36 |
| Issue number | 24 |
| DOIs | |
| State | Published - Jun 13 2024 |
Funding
This work was supported by the Army Research Office (ARO) under Award No. W911NF\u201019\u20101\u20100137 and via an ARO MURI program with Award No. W911NF\u201021\u20101\u20100327, the National Science Foundation under Grant Nos. DMR\u20102122070, 2122071, and 2145797, an Air Force Office of Scientific Research Grant No. FA9550\u201022\u20101\u20100117, and the USC Provost New Strategic Directions for Research Award. The crystal growth equipment were in part supported by an Office of Naval Research grant no. N00014\u201023\u20101\u20102818. The ssNMR research was partially supported by the UCSB NSF Quantum Foundry through Q\u2010AMASE\u2010i program Award No. DMR\u20101906325. The synchrotron research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under Contract No. DE\u2010AC02\u201005CH11231. Electron microscopy was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division and conducted at the Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. Neutron scattering work by M.E.M. and R.P.H. supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division. A portion of this research used resources at the Spallation Neutron Source, supported by DOE, BES, Scientific User Facilities Division. This work used computational resources through allocation DMR160007 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which was supported by NSF Grant Nos. 2138259, 2138286, 2138307, 2137603, and 2138296. H.M. and M.K. acknowledge the support from the Office of Naval Research (N00014\u201020\u20101\u20102297). The authors gratefully acknowledge the use of facilities at the Core Center for Excellence in Nano Imaging at the University of Southern California. Dr. Dominique Massiot is gratefully acknowledged for providing a special build version of the DMfit software and useful discussions on Ti ssNMR. B.Z acknowledges technical assistance from Mythili Surendran, Thomas Orvis, and Harish Kumarasubramanian in collaboration with the related projects.
Keywords
- DFT
- NMR
- STEM
- anisotropy
- refractive index
- structural disorder
- synchrotron diffraction