Chemical Control of Spin-Orbit Coupling and Charge Transfer in Vacancy-Ordered Ruthenium(IV) Halide Perovskites

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, NH4, 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.

Automated summary

Vacancy-ordered double perovskites with Ru-IV halides A(2)RuCl(6) and A(2)RuBr(6) exhibit tunable optical properties and spin-orbit coupling behavior by changing the cation and halide present. The systematic trends in SOC constants are attributed to Ru-X covalency and delocalization of metal d-electrons due to variations in the cation and anion. Magnetic moments of the compounds are temperature dependent due to the non-magnetic ground state with J(eff)=0 caused by SOC.