Chemical Control of Spin‐Orbit Coupling and Charge Transfer in Vacancy‐Ordered Ruthenium(IV) Halide Perovskites
Pratap Vishnoi, Julia L. Zuo, Joya A. Cooley, Linus Kautzsch, Alejandra Gómez‐Torres, Jesse Murillo, Skye Fortier, Stephen D. Wilson, Ram Seshadri, Anthony K. Cheetham
Abstract
Abstract Vacancy‐ordered double perovskites are attracting significant attention due to their chemical diversity and interesting optoelectronic properties. With a view to understanding both the optical and magnetic properties of these compounds, two series of Ru IV halides are presented; A 2 RuCl 6 and A 2 RuBr 6 , where A is K, NH 4 , Rb or Cs. We show that the optical properties and spin‐orbit coupling (SOC) behavior can be tuned through changing the A cation and the halide. Within a series, the energy of the ligand‐to‐metal charge transfer increases as the unit cell expands with the larger A cation, and the band gaps are higher for the respective chlorides than for the bromides. The magnetic moments of the systems are temperature dependent due to a non‐magnetic ground state with J eff =0 caused by SOC. Ru‐ X covalency, and consequently, the delocalization of metal d ‐electrons, result in systematic trends of the SOC constants due to variations in the A cation and the halide anion.