Solid-State Synthesis Enables Enhanced Crystallinity and Tunable Optical Properties in Lanthanum Oxytelluride

Abstract

Elucidating synthetic parameters to produce crystalline solid-state materials with specific properties remains an outstanding obstacle. Oxychalcogenide materials present their own challenges; gaseous reagents are difficult to control and quantify, and reactions cannot be monitored in situ at elevated temperatures. In this paper, we aim to address the lack of fundamental understanding of oxychalcogenides through the synthesis of La₂O₂Te, by two different routes: traditional solid-state and hydrogen gas-assisted methods. We elucidate the two synthetic pathways by X-ray diffraction (XRD) and scanning electron microscopy to demonstrate distinct characteristics between the crystalline and bulk structures, as well as the growth mechanisms of the oxytelluride products. The differences in optical properties at the macroscopic scale correlate with shifts and broadening of the XRD peaks that distinguish two oxytelluride products. The combination of DFT calculations and photoemission yield spectroscopy suggests that oxygen vacancies may explain differences in the optical properties. Finally, this work provides critical synthetic parameters that will enhance the exploratory synthesis of oxychalcogenide materials.