More Like this

1. Yield strength of CeO2 measured from static compression in a radial diamond anvil cell

   https://doi.org/10.1063/5.0097975  

   Huston, Larissa_Q; Couper, Samantha_C; Jacobsen, Matthew; Moss, Eric_K; Miyagi, Lowell; Smith, Jesse_S; Velisavljevic, Nenad; Sturtevant, Blake_T (September 2022, Journal of Applied Physics)

   Cerium oxide (ceria, CeO2) is frequently used as a standard in applications such as synchrotron and x-ray free electron lasers for calibrating x-ray wavelengths and offers the potential for understanding the high pressure properties and deformation mechanisms in a wide range of similar face centered cubic (fcc) materials. In this study, the pressure dependence of the strength of ceria was investigated up to 38 GPa using angle dispersive x-ray diffraction in a radial geometry in a diamond anvil cell. In this experiment, the difference in the stress along the axis of compression and perpendicular to the direction of compression can be determined, giving a quantity known as the differential stress. It was found that the differential stress (t), a measure of the lower bound for yield strength, initially increases rapidly from 0.35 ± 0.06 GPa to 2.2 ± 0.4 GPa at pressures of 1.8 and 3.8 GPa, respectively. Above 4 GPa, t increases more slowly to 13.8 ± 2.6 GPa at a pressure of 38 GPa. The changes in the preferred orientation (texture) of CeO2 with pressure were also measured, allowing for the determination of active deformation mechanisms using an elasto-viscoplastic self-consistent model (EVPSC). It was found that as pressure increased, the [001] direction had a slight preferred orientation along the axis of compression. Our EVPSC model of experimental fiber (cylindrically symmetric) textures and lattice strains were most consistent with dominant slip activity along {111}⟨11¯0⟩. 

   more » « less
2. Competing Deformation Mechanisms in Periclase: Implications for Lower Mantle Anisotropy

   https://doi.org/10.3390/min9110650  

   Lin, Feng; Couper, Samantha; Jugle, Mike; Miyagi, Lowell (November 2019, Minerals)

   Seismic anisotropy is observed above the core-mantle boundary in regions of slab subduction and near the margins of Large Low Shear Velocity Provinces (LLSVPs). Ferropericlase is believed to be the second most abundant phase in the lower mantle. As it is rheologically weak, it may be a dominant source for anisotropy in the lowermost mantle. Understanding deformation mechanisms in ferropericlase over a range of pressure and temperature conditions is crucial to interpret seismic anisotropy. The effect of temperature on deformation mechanisms of ferropericlase has been established, but the effects of pressure are still controversial. With the aim to clarify and quantify the effect of pressure on deformation mechanisms, we perform room temperature compression experiments on polycrystalline periclase to 50 GPa. Lattice strains and texture development are modeled using the Elasto-ViscoPlastic Self Consistent method (EVPSC). Based on modeling results, we find that { 110 } ⟨ 1 1 ¯ 0 ⟩ slip is increasingly activated with higher pressure and is fully activated at ~50 GPa. Pressure and temperature have a competing effect on activities of dominant slip systems. An increasing { 100 } ⟨ 011 ⟩ : { 110 } ⟨ 1 1 ¯ 0 ⟩ ratio of slip activity is expected as material moves from cold subduction regions towards hot upwelling region adjacent to LLSVPs. This could explain observed seismic anisotropy in the circum-Pacific region that appears to weaken near margins of LLVSPs. 

   more » « less
3. Texture Development and Stress–Strain Partitioning in Periclase + Halite Aggregates

   https://doi.org/10.3390/min9110679  

   Lin, F.; Giannetta, M.; Jugle, M.; Couper, S.; Dunleavy, B.; Miyagi, L. (November 2019, Minerals)

   Multiphase materials are widely applied in engineering due to desirable mechanical properties and are of interest to geoscience as rocks are multiphase. High-pressure mechanical behavior is important for understanding the deep Earth where rocks deform at extreme pressure and temperature. In order to systematically study the underlying physics of multiphase deformation at high pressure, we perform diamond anvil cell deformation experiments on MgO + NaCl aggregates with varying phase proportions. Lattice strain and texture evolution are recorded using in-situ synchrotron x-ray diffraction and are modeled using two-phase elasto-viscoplastic self-consistent (EVPSC) simulations to deduce stress, strain, and deformation mechanisms in individual phases and the aggregate. Texture development of MgO and NaCl are affected by phase proportions. In NaCl, a (100) compression texture is observed when small amounts of MgO are present. In contrast, when deformed as a single phase or when large amounts of MgO are present, NaCl develops a (110) texture. Stress and strain evolution in MgO and NaCl also show different trends with varying phase proportions. Based on the results from this study, we construct a general scheme of stress evolution as a function of phase proportion for individual phases and the aggregate. 

   more » « less
4. Recycled calcium carbonate is an efficient oxidation agent under deep upper mantle conditions

   https://doi.org/10.1038/s43247-021-00116-8  

   Tao, Renbiao; Fei, Yingwei (February 2021, Communications Earth & Environment)

   Abstract Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth’s surface by subduction could explain the observed variations. Here we present high-pressure high-temperature multi-anvil experiments to determine the redox reactions between calcium-, magnesium-, or iron-carbonate and ferrous iron-bearing silicate mineral (garnet or fayalite) at conditions representative of subduction zones with intermediate thermal structures. We show that both garnet and fayalite can be oxidized to ferric iron-rich garnets accompanied by reduction of calcium carbonate to form graphite. The ferric iron content in the synthetic garnets increases with increasing pressure, and is correlated with the Ca content in the garnets. We suggest that recycled sedimentary calcium carbonate could influence the evolution of the mantle oxidation state by efficiently increasing the ferric iron content in the deep upper mantle. 

   more » « less
5. Experimental and Computational Studies of Compression and Deformation Behavior of Hafnium Diboride to 208 GPa

   https://doi.org/10.3390/ma15082762  

   Burrage, Kaleb; Lin, Chia-Min; Chen, Cheng-Chien; Vohra, Yogesh K. (April 2022, Materials)

   The compression behavior of the hexagonal AlB2 phase of Hafnium Diboride (HfB2) was studied in a diamond anvil cell to a pressure of 208 GPa by axial X-ray diffraction employing platinum as an internal pressure standard. The deformation behavior of HfB2 was studied by radial X-ray diffraction technique to 50 GPa, which allows for measurement of maximum differential stress or compressive yield strength at high pressures. The hydrostatic compression curve deduced from radial X-ray diffraction measurements yielded an ambient-pressure volume V0 = 29.73 Å3/atom and a bulk modulus K0 = 282 GPa. Density functional theory calculations showed ambient-pressure volume V0 = 29.84 Å3/atom and bulk modulus K0 = 262 GPa, which are in good agreement with the hydrostatic experimental values. The measured compressive yield strength approaches 3% of the shear modulus at a pressure of 50 GPa. The theoretical strain-stress calculation shows a maximum shear stress τmax~39 GPa along the (1−10) [110] direction of the hexagonal lattice of HfB2, which thereby can be an incompressible high strength material for extreme-environment applications. 

   more » « less