Perovskite or double perovskite structures are adopted by a variety of compounds. They can have a range of applications, e.g., in optoelectronics. The stability and band gap of the materials need to be optimized for the specific type of application. Oxide perovskites, for example, can show higher stabilities than halide perovskite compounds.

Optimal band gaps for, e.g., solar cell applications are often in the near-IR range. For achieving these bands gaps, the inclusion of heavier elements can be useful. For example, the band gap of the oxide double perovskite Ba₂AgIO₆ could be optimized by replacing Ag with the heavier Au. However, there had been no gold oxide perovskites of this type reported so far.

Tyrel M. McQueen, Johns Hopkins University, Baltimore, MD, USA, and colleagues have synthesized the first gold-containing double perovskite, Ba₂AuIO₆ (pictured) and compared it with the “lighter” analogues Ba₂AgIO₆ and Ba₂NaIO₆. The team used hydrothermal syntheses to prepare Ba₂AgIO₆ and Ba₂AuIO₆ from either Au₂O₃ or Ag₂O, Ba(OH)₂·8H₂O, and H₅IO₆. Ba₂NaIO₆ was synthesized from NaIO₄ and Ba(OH)₂·8H₂O via a solid-state reaction.

The products were characterized using X-ray diffraction, confirming the double-perovskite structure. Ba₂NaIO₆ has a cubic perovskite structure, while Ba₂AuIO₆ and Ba₂AgIO₆ show a monoclinic distortion. The band gaps of Ba₂AuIO₆ and Ba₂AgIO₆ are ca. 1.3 eV and ca. 2.1 eV, respectively. These values are promising for solar and other optoelectronic applications, but the stability of the compounds still needs improvement.

• A Gold(I) Oxide Double Perovskite: Ba₂AuIO₆,
  Elizabeth A. Pogue, Jack Bond, Cassandra Imperato, John B. S. Abraham, Natalia Drichko, Tyrel M. McQueen,
  J. Am. Chem. Soc. 2021.
  https://doi.org/10.1021/jacs.1c08241