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Under conditions of high stress or low temperature, glide of dislocations plays an important role in the deformation of UO 2. In this paper, the Peierls-Nabarro model is used to calculate the core widths and Peierls stresses of ½<110> edge and screw dislocations gliding on {100}, {110}, and {111}. The energy of the inelastic displacement field in the dislocation core is parameterized using generalized stacking fault energies, which are calculated atomistically using interatomic potentials. We use seven different interatomic potential models, representing the variety of different models available for UO 2. The different models broadly agree on the relative order of the strengths of the different slip systems, with the 1/2<110>{100} edge dislocation predicted to be the weakest slip system and 1/2<110>{110} the strongest. However, the calculated Peierls stresses depend strongly on the interatomic potential used, with values ranging between 2.7-12.9 GPa for glide of 1/2<110>{100} edge dislocations, 16.4-32.3 GPa for 1/2<110>{110} edge dislocations, and 6.8-13.6 GPa for 1/2<110>{111} edge dislocations. The glide of 1/2<110> screw dislocations in UO 2 is also found to depend on the interatomic potential used, with some models predicting similar Peierls stresses for glide on {100} and {111}, while others predict a unique easy glide direction. Comparison with previous fully atomistic calculations show that the Peierls-Nabarro model can accurately predict dislocation properties in UO 2 .

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9Omphacite, a clinopyroxene mineral with two distinct crystallographic sites, M1 and M2, and 10 composition intermediate between diopside and jadeite, is abundant throughout the Earth's upper 11 mantle, and is the dominant mineral in subducted oceanic crust. Unlike the end-members, 12 omphacite exists in two distinct phases, a P2/n ordered phase at low temperature and a high-13 temperature C2/c disordered phase. The crystal structure and full elastic constants tensor of ordered 14 P2/n omphacite have been calculated to 15 GPa using plane-wave density functional theory. Our 15 results show that several of the elastic constants, notably C 11 , C 12 , and C 13 deviate from linear-16 mixing between diopside and jadeite. The anisotropy of omphacite decreases with increasing 17 pressure and, at 10 GPa, is lower than that of either diopside or jadeite. The effect of cation disorder 18 is investigated through force-field calculations of the elastic constants of Special Quasirandom 19 2 Structures supercells with simulated disorder over the M2 sites only, and over both cation sites. 20These show that cation order influences the elasticity, with some components displaying particular 21 sensitivity to order on a specific cation site. C 11 , C 12 , and C 66 are sensitive to disorder on M1, while 22 C 22 is softened substantially by disorder on M2, but insensitive to disorder on M1. This shows that 23 the elasticity of omphacite is sensitive to the degree of disorder, and hence the temperature. We 24 expect these results to be relevant to other minerals with order-disorder phase transitions, implying 25 that care must be taken when considering the effects of composition on seismic anisotropy. 26

Ionogels are hybrid materials formed by impregnating the pore space of a solid matrix with a conducting ionic liquid. By combining the properties of both component materials, ionogels can act as self-supporting electrolytes in Li batteries. In this study, molecular dynamics simulations are used to investigate the dependence of mechanical properties of silica ionogels on solid fraction, temperature, and pore width. Comparisons are made with corresponding aerogels. We find that the solid matrix fraction increases the moduli and strength of the ionogel. This varies nonlinearly with temperature and strain rate, according to the contribution of the viscous ionic liquid to resisting deformation. Owing to the temperature and strain sensitivity of the ionic liquid viscosity, the mechanical properties approach a linear mixing law at high temperature and low strain rates. The median pore width of the solid matrix plays a complex role, with its influence varying qualitatively with deformation mode. Narrower pores increase the relevant elastic modulus under shear and uniaxial compression but reduce the modulus obtained under uniaxial tension. Conversely, shear and tensile strength are increased by narrowing the pore width. All of these pore size effects become more pronounced as the silica fraction increases. Pore size effects, similar to the effects of temperature and strain rate, are linked to the ease of fluid redistribution within the pore space during deformation-induced changes in the geometry of the pores.