Magnetic and Intercalation Properties of BaRu2O6 and SrRu2O6

Ruthenium oxides have been extensively studied for their attractive magnetic properties. For instance, the honeycomb-layered ruthenate SrRu2O6 has attracted a lot of attention in the last years for its unusually high Néel temperature (565 K), which is among the highest for 4d transition-metal oxides. Motivated by this intriguing feature, several authors suggested to tune the magnetic properties via atomic substitutions. However, in spite of intense efforts, this could not happen because of the instability of the targeted phases at high temperature. We unlocked this bottleneck and succeeded in synthetizing the Ba-based analogue BaRu2O6 by a microwave-assisted hydrothermal process. We describe herein for the first time its structure and physico-chemical properties. Synchrotron X-ray, neutron powder diffraction, and transmission electron microscopy confirm this new compound to be structurally related to SrRu2O6 with however a different oxygen layer stacking. Thereafter, BaRu2O6 is shown to be an antiferromagnet with a high Néel temperature (525 K), and this behavior is discussed in light of its crystal structure. Finally, both SrRu2O6 and BaRu2O6 can electrochemically insert lithium, and the interlayer alkali-earth cations act as pillars, which strongly affect the structural evolution through lithiation. Our results offer new keys toward a better understanding of the magnetic and electrochemical properties of complex ruthenium-based layered oxides.