High-Pressure Synthesis of Manganese Oxyhydride with Partial Anion Order.

The high-pressure synthesis of a manganese oxyhydride LaSrMnO3.3H0.7 is reported. Neutron and X-ray Rietveld analyses showed that this compound adopts the K2NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen-deficient phases down to LaSrMnO3.5. This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition-metal oxyhydrides. Magnetic susceptibility revealed a spin-glass transition at 24 K that is due to competing ferromagnetic (Mn2+–Mn3+) and antiferromagnetic (Mn2+–Mn2, Mn3+–Mn3+) interactions.