Defect structure of yttria-stabilized hafnia nanoparticles

Area of Science:

• Materials Science
• Solid State Chemistry
• Nanotechnology

Background:

• High-temperature polymorphs of hafnia (HfO₂) are crucial for electronics and fuel cells.
• Stabilizing these phases at ambient conditions is achievable via aliovalent substitution and nanosize effects.
• Yttria stabilization of hafnia (YSH) introduces cation disorder and oxygen vacancies.

Purpose of the Study:

• To determine the average and local structure of yttria-stabilized hafnia (YSH) nanoparticles.
• To investigate the formation mechanism and crystallization kinetics of YSH nanoparticles.

Main Methods:

• Synchrotron powder X-ray diffraction (PXRD) and pair distribution function (PDF) analysis.
• Continuous flow solvothermal synthesis followed by high-temperature annealing.
• In situ X-ray total scattering experiments.

Main Results:

• Phase-pure crystalline Hf_1-xY_xO_2-x/2 nanoparticles were synthesized, with cubic phase stabilization achieved at 13 at% Y³⁺.
• The average structure is cubic fluorite, but local displacive disorder exists due to oxygen vacancies.
• The Zr₃Y₄O₁₂ structure serves as a good model for YSH local structure.
• In situ studies revealed amorphous phase precipitation followed by crystallization, with kinetics dependent on temperature and doping level.

Conclusions:

• Yttria substitution effectively stabilizes the cubic phase of hafnia nanoparticles at ambient conditions.
• Local structural disorder is a key feature of YSH, impacting its properties.
• The synthesis method allows for controlled formation and crystallization of YSH nanoparticles.