Structural, optical and electronic properties of Ni_1- Co O in the complete composition range

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Investigating ternary solid solutions like NiₓCo₁₋ₓO is crucial for understanding structure-property relationships.
• Phase-pure materials are essential for accurate characterization of solid solutions.

Purpose of the Study:

• To elucidate the crystallographic and electronic structures of NiₓCo₁₋ₓO solid solutions.
• To correlate structural parameters with electronic properties, specifically the optical gap.

Main Methods:

• X-ray Diffraction (XRD) for crystallographic analysis.
• X-ray Absorption Spectroscopy (XAS), including EXAFS and XANES, for electronic structure and bonding.
• Diffuse reflectivity measurements for optical gap determination.

Main Results:

• Lattice parameter and bond lengths increase linearly with cobalt content, following Vegard's law with minimal local distortion.
• Optical gap does not vary linearly with composition and shows no bowing.
• Conduction band edge energy variation directly correlates with the optical gap variation.

Conclusions:

• The electronic structure, particularly the conduction band, plays a dominant role in determining the optical gap of NiₓCo₁₋ₓO.
• XAS at O K-edge and Ni/Co K- and L-edges provides insights into unoccupied O 2p-metal 3d hybridized states and their relation to bond lengths.