High Pressure Brillouin Spectroscopy and X-ray Diffraction of Cerium Dioxide

Mungo Frost,John D. Lazarz,Hong Yang,Arianna E. Gleason,Abraham L. Levitan,Vitali B. Prakapenka,Siegfried H. Glenzer,Sergey N. Tkachev,Peihao Sun

doi:10.3390/ma14133683

Abstract

Simultaneous high-pressure Brillouin spectroscopy and powder X-ray diffraction of cerium dioxide powders are presented at room temperature to a pressure of 45 GPa. Micro- and nanocrystalline powders are studied and the density, acoustic velocities and elastic moduli determined. In contrast to recent reports of anomalous compressibility and strength in nanocrystalline cerium dioxide, the acoustic velocities are found to be insensitive to grain size and enhanced strength is not observed in nanocrystalline CeO. Discrepancies in the bulk moduli derived from Brillouin and powder X-ray diffraction studies suggest that the properties of CeO are sensitive to the hydrostaticity of its environment. Our Brillouin data give the shear modulus, = 63 (3) GPa, and adiabatic bulk modulus, = 142 (9) GPa, which is considerably lower than the isothermal bulk modulus, 230 GPa, determined by high-pressure X-ray diffraction experiments.

Highlights

Brillouin spectroscopy allows for the direct determination of acoustic velocities and elastic moduli of materials, and is ideally suited for measuring these at high-pressures in diamond anvil cells [1]
Cerium dioxide powders of nano- and micro-scale grain size were loaded without a pressure transmitting media (PTM) into diamond anvil cells equipped with wide angle Bohler—Almax anvils with 300 μm diameter culets
This suggests that the observations may be due to changes in the nonhydrostatic strain on the sample as PTMs harden at high pressure [17], or from more complex interactions between the nanoparticles and PTM, and are not representative of cerium dioxide alone under hydrostatic strain

Summary

Introduction

Brillouin spectroscopy allows for the direct determination of acoustic velocities and elastic moduli of materials, and is ideally suited for measuring these at high-pressures in diamond anvil cells [1]. It is well complemented by X-ray diffraction which allows a direct measurement of the density of the compressed material. CeO2 , has a number of uses including catalysis [2], sensors [3], and an emerging application as an oxygen ion conductor in solid oxide fuel cells [4] It is widely used as a non-hazardous analogue for the development of ceramic nuclear fuels, where its physical properties mimic those of oxide nuclear fuels [5,6,7]. Understanding its polycrystalline high-pressure behavior is vital where deep storage systems may collapse or be subject to seismic activity

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