Anionic and Magnetic Ordering in Rare Earth Tantalum Oxynitrides with an n = 1 Ruddlesden-Popper Structure.

Area of Science:

• Solid-state chemistry
• Materials science
• Inorganic chemistry

Background:

• Rare earth transition metal oxynitrides are an emerging class of materials with potential applications in catalysis and electronics.
• The Ruddlesden-Popper (RP) phases, characterized by their layered perovskite-like structures, offer tunable properties based on their composition and structure.
• Understanding the synthesis, structure, and properties of new RP phases is crucial for developing advanced functional materials.

Purpose of the Study:

• To synthesize and characterize new rare earth transition metal oxynitrides with an n=1 Ruddlesden-Popper structure.
• To investigate the anion stoichiometry, crystal structure, and magnetic properties of these novel compounds.
• To explore the relationship between crystal structure, anion ordering, and magnetic behavior.

Main Methods:

• Solid-state reaction of metal nitrides and oxides/oxynitrides under N2 gas at high temperatures (1200–1700 °C).
• Synchrotron X-ray powder diffraction and electron diffraction for crystal structure determination.
• Neutron powder diffraction for detailed anion ordering analysis.
• Magnetization measurements to probe magnetic properties.

Main Results:

• Successful synthesis of new R2TaO4-xNx compounds (R = La, Ce, Nd, Eu) with n=1 RP structure.
• Orthorhombic (Pccn) and tetragonal (I41/acd) crystal structures were observed, with varying anion stoichiometries.
• Neutron diffraction revealed specific nitrogen ordering within the tantalum octahedron in Ce2TaO1.19N2.81.
• Magnetic ordering was observed in Ce and Eu compounds at low temperatures, while Nd remained paramagnetic.

Conclusions:

• The study presents the first rare earth transition metal oxynitrides with an n=1 RP structure.
• The diverse crystal structures and anion ordering highlight the tunability of these materials.
• The observed magnetic properties are linked to the specific rare earth element and crystal structure, offering insights for magnetic material design.