Anion diffusion in Y- and N-doped ZrO2.

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Zirconia (ZrO2) is a key material in various high-temperature applications.
• Understanding anion diffusion mechanisms in doped zirconia is crucial for optimizing its performance.
• Previous studies have investigated diffusion using tracer measurements, but direct observation of anion motion is needed.

Purpose of the Study:

• To determine the effective single particle potentials for O2 and N3- anions in yttria-doped ZrO2.
• To elucidate the diffusion pathways and mechanisms of these anions at high temperatures.
• To investigate the influence of local order and thermal vibrations on the diffusion process.

Main Methods:

• Single crystal neutron diffraction was employed to study three samples of ZrO2 doped with varying amounts of Y and N.
• High-temperature measurements were conducted to observe anion motion.
• Analysis of diffraction data allowed for the determination of single particle potentials and diffusion pathways.

Main Results:

• Diffusion jumps for O2 and N3- anions were observed to occur directly to vacant nearest neighbor anion sites.
• These jumps predominantly follow (100)-directions, passing through the edges of surrounding cation tetrahedra.
• Activation enthalpies for migration were determined: 1.09 eV for O and 1.99 eV for N, consistent with tracer diffusion data.
• The diffusion process is significantly influenced by local short-range order and anharmonic thermal vibrations.

Conclusions:

• The study provides direct evidence for the anion diffusion mechanism in doped zirconia.
• Phonon interactions play a critical role and must be considered in models describing the diffusion process.
• The findings contribute to a deeper understanding of ionic conductivity in solid electrolytes.