Comparative High-Pressure Study on Rare-Earth Entropy Fluorite-Type Oxides

Area of Science:

• Materials Science
• Solid State Chemistry
• High-Pressure Physics

Background:

• Rare-earth oxides with fluorite structures are crucial in advanced materials.
• Configurational entropy significantly influences the properties of high-entropy materials.
• Understanding material behavior under extreme pressure is vital for technological applications.

Purpose of the Study:

• To comparatively investigate the high-pressure structural response of two fluorite-type rare-earth oxides with varying configurational entropy.
• To elucidate the mechanisms behind structural stability and vibrational property changes under extreme compression.
• To explore the role of cationic disorder in the resilience of these materials.

Main Methods:

• Synchrotron-based powder X-ray diffraction up to 30 GPa.
• Raman spectroscopy up to 20 GPa.
• Analysis of compressibility, vibrational modes, and structural phase transitions.

Main Results:

• Both (CePr)-O_2-δ and (CePrLa)-O_2-δ retained the fluorite structure, with an anomaly (compressibility plateau, vibrational mode changes) between 9-16 GPa attributed to lattice distortions.
• (CePrLa)-O_2-δ showed amorphization above 22 GPa, indicating reduced stability.
• A slight decrease in bulk modulus post-anomaly suggested lattice softening; Raman data indicated suppression of F_2g mode with disorder and partial reordering under pressure.

Conclusions:

• Configurational entropy, cation size, and pressure intricately govern the structural stability and vibrational properties of rare-earth high-entropy oxides.
• Local lattice distortions and bond angle bending, rather than abrupt phase transitions, characterize the observed anomaly.
• The study provides insights into the resilience and disorder mechanisms in these materials under extreme conditions.