Density-Driven Investigations of Ruthenium Binary Compounds RuX2 (X = O, S, N)

Exploration and fine-tuning of the energy landscape of materials can be accessed by means of changes in material density, a key principle of high pressure research. Density-driven changes impact variations in oxidation states and coordination numbers for the element constituents of a compound. Pressure-induced modification of intrinsic density can promote the formation of new materials, variations in physical properties, and transformations in crystallographic symmetry. With this as our foundation, we focus on ruthenium binary compounds - altering the anion species to change electronegativity while probing pressure and temperature effects. This led us to the present study of ruthenium oxide RuO2, nitride RuN2, and sulfide RuS2, wherein we measure the pressure response of physical properties and characterize corresponding crystal structures. We report the discovery of multiple new high pressure phases of RuO2, the first high pressure experiments on RuS2, and the formation of RuN2 while seeking to explore new materials through high-pressure, high-temperature synthesis. These works utilized a combination of high pressure synchrotron x-ray diffraction, in-house Raman spectroscopy, diamond anvil cell electrical transport, laser heating, and cryostat techniques, with additional support and insight from DFT simulations.