ABSTRACT
Heteroanionic compounds continue to gain interest in materials design because the expanded composition space provides opportunities to discover new phases and tune physical properties. Among heteroanionic materials, oxytellurides comprised of oxygen and tellurium anions are relatively underexplored despite the significant role of tellurium in emerging technologies. Herein, we present synthetic strategies toward oxytelluride Ln2O2Te (Ln = La-Pr), whose layered structure features square nets of Te2- anions. Upon heating in H2 or air, we find a reversible phase transition between the oxytelluride and tellurate Ln2TeO6 (Ln = La, Pr), wherein Te is octahedrally coordinated and a 6+ oxidation state is corroborated by bond valence analysis. We use X-ray diffraction along with thermogravimetric analyses to confirm the presence of oxytelluride and tellurate phases and emphasize key structural distinctions. In contrast, we find that Ce2O2Te decomposes to form CeO2 and demonstrate the instability of Ce2O2Te in ambient conditions by timelapse X-ray diffraction and diffuse-reflectance spectroscopy experiments. Band gaps of Ln2O2Te (Ln = La-Pr) were estimated from diffuse-reflectance spectroscopy in the semiconducting range â¼2.1-2.7 eV, while band gaps for La2TeO6 and Pr2TeO6 were much larger at â¼4.3 and â¼3.7 eV, respectively.
