Exsolution of SrO during the Topochemical Conversion of LaSr₃CoRuO₈ to the Oxyhydride LaSr₃CoRuO₄H₄

Abstract

Reaction of the <i>n</i> = 1 Ruddlesden-Popper oxide LaSr₃CoRuO₈ with CaH₂ yields the oxyhydride phase LaSr₃CoRuO₄H₄ via a topochemical anion exchange. Close inspection of the X-ray and neutron powder diffraction data in combination with HAADF-STEM images reveals that the nanoparticles of SrO are exsolved from the system during the reaction, with the change in cation stoichiometry accommodated by the inclusion of <i>n</i> > 1 (Co/Ru)<i>_n</i>O_<i>n</i>+1H_2<i>n</i> "perovskite" layers into the Ruddlesden-Popper stacking sequence. This novel pseudotopochemical process offers a new route for the formation of <i>n</i> > 1 Ruddlesden-Popper structured materials. Magnetization data are consistent with a LaSr₃Co⁺Ru²⁺O₄H₄ (Co⁺, d⁸, <i>S</i> = 1; Ru²⁺, d⁶, <i>S</i> = 0) oxidation/spin state combination. Neutron diffraction and μ⁺SR data show no evidence for long-range magnetic order down to 2 K, suggesting the diamagnetic Ru²⁺ centers impede the Co-Co magnetic-exchange interactions.