Resolving a structural issue in cerium-nickel-based oxide: a single compound or a two-phase system?

Area of Science:

• Materials Science
• Inorganic Chemistry
• Nanotechnology

Background:

• Cerium nickelate (CeNiO3) is a novel LnNiO3 compound with potential catalytic applications.
• Previous literature reports have not accurately defined the structure of CeNiO3.
• Understanding the precise structure is crucial for optimizing its catalytic performance.

Purpose of the Study:

• To synthesize nanocrystalline CeNiO3 (RB1), CeO2, and NiO.
• To compare the structure of RB1 with an equimolar physical mixture of CeO2 and NiO.
• To elucidate the true crystal structure of CeNiO3 using advanced characterization techniques.

Main Methods:

• Modified citrate aqueous sol-gel route for synthesis.
• Laboratory powder X-ray diffraction (PXRD), SAED, TEM-EDS, Raman spectroscopy, XPS, TGA for initial characterization.
• Synchrotron-based methods including atomic pair distribution function analysis (PDF), XANES, and EXAFS for detailed structural analysis.

Main Results:

• Clear structural and property differences were observed between RB1 and the physical mixture (CeO2 + NiO).
• Advanced synchrotron analyses provided detailed insights into the complex structure of RB1.
• Three structural models were proposed for RB1: a single-phase pyrochlore (Ce2Ni2O7) or a two-phase system (CeO2 + NiO or Ce1-xNixO2 + NiO).

Conclusions:

• The study successfully differentiated the structure of synthesized CeNiO3 (RB1) from a simple physical mixture.
• The precise crystallographic structure of CeNiO3 remains complex and requires further investigation.
• The findings provide a foundation for future research into the catalytic applications of CeNiO3.