Discovery of highly-polarizable semiconductors BaZrS3 and Ba3Zr2S7

• Published in: arXiv.org 2020-06
• Main Authors: Filippone, Stephen, Zhao, Boyang, Niu, Shanyuan, Koocher, Nathan Z, Silevitch, Daniel, Fina, Ignasi, Rondinelli, James M, Ravichandran, Jayakanth, Jaramillo, R
• Format: Article
• Language: English
• Subjects: Chalcogenides; Crystal structure; Current carriers; Dielectric strength; Electronic structure; Energy gap; Infrared radiation; Inorganic materials; Perovskites; Semiconductors; Single crystals; Stiffness; Zirconium
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2006.10655

There are few known semiconductors exhibiting both strong optical response and large dielectric polarizability. Inorganic materials with large dielectric polarizability tend to be wide-band gap complex oxides. Semiconductors with strong photoresponse to visible and infrared light tend to be weakly polarizable. Interesting exceptions to these trends are halide perovskites and phase-change chalcogenides. Here we introduce complex chalcogenides in the Ba-Zr-S system in perovskite and Ruddlesden-Popper structures as a new family of highly polarizable semiconductors. We report the results of impedance spectroscopy on single crystals that establish BaZrS3 and Ba3Zr2S7 as semiconductors with low-frequency relative dielectric constant (\({\epsilon}_0\)) in the range 50 - 100, and band gap in the range 1.3 - 1.8 eV. Our electronic structure calculations indicate the enhanced dielectric response in perovskite BaZrS3 versus Ruddlesden-Popper Ba3Zr2S7 is primarily due to enhanced IR mode-effective charges, and variations in phonon frequencies along \(\langle 001 \rangle\); differences in the Born effective charges and the lattice stiffness are of secondary importance. This combination of covalent bonding in crystal structures more common to complex oxides results in a sizable Fr\"ohlich coupling constant, which suggests that charge carriers are large polarons.