This is a project to develop a novel new x-ray diffraction technique to determine the stress distribution under in-situ high pressure conditions corresponding to the mantle interior. With this technique, studies such as stress-induced preferred orientation and yield strength measurements of high-pressure minerals, which are necessary to further understand the dynamics of the mantle, will become possible. These measurements can be made either in multi-anvil high pressure apparatus or in diamond anvil cells. A reliable method to determine the uniaxial stress under high pressure by measuring the anisotropic compression of standard materials using the new high-precision x-ray diffraction technique will be established. This technique will be applied to study the stress-induced preferred orientation in beta-Mn2GeO4 (chosen as a model system for the (Mg-Fe)SiO4 mantle olivine) as it undergoes the polymorphic transformation from its olivine- phase to beta-phase under the influence of uniaxial stress. The PI will apply the new technique to study the changes in the yield strength of alkali halides across the B1-B2 phase boundary, to look for possible superplasticity at the transition and to determine the elastic constants of the B2 phase. The experiments will be conducted in collaboration with four Japanese high- pressure scientists using the MAX-80 cubic-anvil high-pressure system stationed at the high-energy (maximum - 140KeV) synchrotron radiation x-ray source at the national Laboratory for High Energy Physics in Tsukuba, Japan.
