Hidden Complexity in the TiO₂ to TiN Transformation Unveiled through Compositional Analysis.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• Heteroanionic materials, specifically oxynitrides, are crucial for tuning electronic and structural properties.
• Titanium dioxide (TiO2) serves as a versatile precursor for creating novel oxynitride compounds.

Purpose of the Study:

• To synthesize titanium oxynitride (TiOₓNᵧ) from TiO2 by heating in ammonia (NH3).
• To quantitatively determine the composition of the synthesized TiOₓNᵧ.
• To investigate the transformation kinetics and mechanism of TiO2 to TiOₓNᵧ.

Main Methods:

• Quantitative composition analysis using the indophenol blue method and thermogravimetric analysis (TGA).
• Qualitative compositional confirmation and oxidation state analysis via X-ray absorption spectroscopy (XAS).
• Mechanism elucidation using extended X-ray absorption fine structure (EXAFS) and comparison across different TiO2 nanoparticle morphologies.

Main Results:

• The transformation of TiO2 to TiOₓNᵧ proceeds in two distinct kinetic steps: a rapid phase transition followed by slower nitrogen incorporation.
• Particle size influences transformation kinetics, with smaller particles reacting faster.
• EXAFS data indicates the formation of an amorphous intermediate phase during the transformation process.
• XAS confirms the reduction of Ti(IV) to Ti(III) during the conversion.

Conclusions:

• Accurate determination of oxygen/nitrogen ratios is vital for understanding oxynitride chemistry and structure-property relationships.
• The transformation mechanism involves an amorphous intermediate, highlighting the complexity of oxynitride formation.
• This research provides a detailed understanding of the synthesis and transformation pathways of titanium oxynitrides.