Atomic-scale structure of ZrO₂: Formation of metastable polymorphs

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Metastable phases are crucial for technological applications but their stabilization mechanisms and atomic structures remain poorly understood.
• Kinetically trapped metastable phases arise from processing routes like thermal treatment, doping, or irradiation.
• Understanding the atomic-scale nature of metastable phases is key to harnessing their properties.

Purpose of the Study:

• To elucidate the underlying structural mechanisms and atomic-scale nature of metastable tetragonal zirconia.
• To investigate the role of processing routes, specifically ion irradiation and nanocrystallinity, on the stabilization of metastable phases.
• To provide insights into the synthesis and recovery of functional metastable materials.

Main Methods:

• Neutron total scattering experiments were employed to investigate ion-irradiated and nanocrystalline zirconia.
• Analysis focused on determining the structure and atomic arrangement within the metastable phase.
• The study utilized advanced scattering techniques to probe short-range and long-range order.

Main Results:

• Metastable tetragonal zirconia (ZrO₂) exhibits an underlying structure of ferroelastic, orthorhombic nanoscale domains.
• These domains are stabilized by an intricate network of domain walls.
• The observed long-range tetragonal structure is an ensemble average of these dynamic orthorhombic domains.

Conclusions:

• The true structure of metastable tetragonal zirconia is heterogeneous, characterized by nanoscale orthorhombic domains.
• Domain wall networks play a critical role in stabilizing these metastable phases.
• This findings are broadly applicable to other nonequilibrium materials, offering insights into their synthesis and property recovery.