Hydrothermal Synthesis of a B-Site Magnetic Ruthenate Pyrochlore

The pyrochlore oxide (Ce IV 0.67 Na 0.33 ) 2 Ru IV 2 O 7 crystallizes directly as a phase-pure sample, without the need for postsynthesis annealing, from aqueous solutions of Ru 3+, Ce 3+, and sodium hydroxide in the presence of hydrogen peroxide as oxidizing agent at less than 250 °C. The structure has been refined using powder neutron diffraction and is consistent with electron diffraction and EDXA analysis performed using transmission electron microscopy (cubic Fd 3̅ m with a = 10.1659(1) Å). The pyrochlore phase is metastable and upon heating to ∼400 °C begins to phase separate to ultimately yield a mixture including Na 2 Ru 4 O 9, RuO 2, Ce 2 O 3, and CeO 2 . Magnetization measurements confirm that the material is a new example of a B-site magnetic pyrochlore, analogous to the known phase Y 2 Ru 2 O 7, but that show evidence for magnetic frustration at low temperatures. Heat capacity measurements and low-temperature neutron diffraction indicate the possibility of spin-glass-like behavior with no evidence of long-range magnetic order achieved at low temperature.