Discovery of highly-polarizable semiconductors BaZrS3 and Ba3Zr2S7

TL;DR

This paper introduces BaZrS3 and Ba3Zr2S7 as new highly polarizable semiconductors with strong optical response and large dielectric constants, expanding the family of materials suitable for optoelectronic applications.

Contribution

The study identifies and characterizes BaZrS3 and Ba3Zr2S7 as novel highly polarizable semiconductors with specific dielectric and electronic properties, using experimental and computational methods.

Findings

BaZrS3 has a dielectric constant of 50-100.

Band gaps range from 1.3 to 1.8 eV.

Enhanced dielectric response is linked to IR mode-effective charges.

Abstract

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.