Hydrothermal Synthesis of a B-Site Magnetic Ruthenate Pyrochlore

• Published in: Crystal growth & design Vol. 10; no. 8; pp. 3819 - 3823
• Main Authors: Darton, Richard J, Turner, Scott S, Sloan, Jeremy, Lees, Martin R, Walton, Richard I
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 04.08.2010
• Subjects: Condensed matter: structure, mechanical and thermal properties; Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction; Electron diffraction and scattering; Exact sciences and technology; Neutron diffraction and scattering; Physics; Single-crystal and powder diffraction; Structure of solids and liquids; crystallography; Pyrochlore; Cubic lattices; Spin glasses; Annealing; Hydroxides; Hydrogen peroxide; Magnetization; Metastable phases; Neutron diffraction; Electron diffraction; Long-range order; Heat capacity; Ruthenium oxide; Cerium oxide; Heat treatments; Powder pattern; Transmission electron microscopy; Ruthenates; Hydrothermal synthesis; Sodium; Aqueous solutions; Magnetic frustration
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg100728s

The pyrochlore oxide (CeIV 0.67Na0.33)2RuIV 2O7 crystallizes directly as a phase-pure sample, without the need for postsynthesis annealing, from aqueous solutions of Ru3+, Ce3+, 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 Fd3̅m 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 Na2Ru4O9, RuO2, Ce2O3, and CeO2. Magnetization measurements confirm that the material is a new example of a B-site magnetic pyrochlore, analogous to the known phase Y2Ru2O7, 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.