Anion order in perovskite oxynitrides

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Perovskite-type transition-metal oxynitrides are emerging materials with tunable properties.
• Understanding anion-ordering principles is crucial for controlling their optical, photocatalytic, dielectric, and magnetoresistive characteristics.
• Previous studies lacked clarity on the fundamental rules governing anion ordering in these compounds.

Purpose of the Study:

• To investigate the anion-ordering principles in representative perovskite-type oxynitrides, specifically SrMO(2)N (M = Nb, Ta).
• To elucidate the relationship between anion order and the structural and electronic properties of these materials.

Main Methods:

• Utilized neutron and electron diffraction techniques to analyze the crystal structure of SrMO(2)N compounds.
• Examined materials at various temperatures, including high temperatures up to 750 °C.
• Performed local structure predictions for a wider range of oxynitride perovskites.

Main Results:

• Revealed a robust 1O/2(O(0.5)N(0.5)) partial anion order in SrMO(2)N, stable up to at least 750 °C.
• Demonstrated that this anion order dictates the rotation of MO(4)N(2) octahedra in the room-temperature superstructure.
• Identified local cis-ordering of nitrides within octahedra, driven by covalency, leading to disordered zigzag M-N chains.

Conclusions:

• The study clarifies anion-ordering principles in perovskite oxynitrides, establishing a link between anion order and structural motifs.
• The findings provide a foundation for predicting local structures across the oxynitride perovskite family.
• Future research should focus on controlling anion order and dimensionality to tune material properties for specific applications.