Anion Composition Control and Magnetic Short- and Long-Range Order in Transition Metal Oxide Hydrides

Abstract

Lanthanide transition metal oxide hydride phases, LnSrCoO3+αHβ (Ln = Pr, Nd), with variable H and O content, have been prepared by topotactic reduction of the parent n = 1 Ruddlesden−Popper phase, LnSrCoO4, with CaH2 via a LnSrCoO3.5 (Co2+) intermediate. The hydride anions occupy the site bridging the cations along the shorter in-plane direction in the CoOH plane. Substitution of oxide for hydride anions is incomplete leading to the compositions NdSrCoO3.084(4)H0.796(3) (A), NdSrCoO3.210(3)H0.580(6) (B), and PrSrCoO3.160(4)H0.680(7) (E) as determined by Rietveld refinement using powder neutron diffraction data. Diffraction, thermal gravimetry, and X-ray absorption spectroscopy show that the Co oxidation state remains close to +2 despite variation in hydride content. Variable temperature neutron powder diffraction studies show that the lanthanide size and H content strongly influence the Neel temperature (410 K (A), 375 K (B), and 445 K (E)). All the materials are antiferromagnets. Magnetic short-range ord...