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Seminar on "Deformation of Solids at Multimegabar Stresses: Strength and Elasticity from X-ray Diffraction Data" 
Thursday, 17 January 2013,  3:00 -  4:30
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The stresses in the range of several megabars can be generated by compressing matter

between two flat diamond tips (diamond anvil cell). The diamond anvil cells have been

extensively used to study the effect of stress (pressure) on the crystalline state of matter

through diffraction methods. These studies yield information on the pressure–volume

relation (equation of state; EoS) and pressure induced phase transitions. For a meaningful

comparison of the experimental results with those of the first-principles computations, it is

desirable to conduct the diffraction experiments under hydrostatic pressure. Generation of

truly hydrostatic pressure in the anvil devices, particularly above 50 GPa, has remained a

challenge. Part of the problem lies in the detection of hydrostaticity of the sample pressure.

Above 100 GPa, the pressures unavoidably become nonhydrostatic. It turns out that the

diffraction data taken under nonhydrostatic pressure contain a variety of information that is

absent in the hydrostatic pressure data. A proper analysis of the nonhydrostatic

compression data with the help of lattice–strain equations makes it possible to derive the

pressure dependences of compressive strength and single crystal elastic moduli in addition

to the EoS corresponding to the hydrostatic pressure. This talk will summarize the current

status of the lattice–strain theory and discuss some recent studies conducted on solids of

geophysical interest. The experimental and theoretical developments in this area have led to

the modeling of the deformation behavior of polycrystalline solids consisting of elastically

anisotropic crystallites. A brief mention of this newly emerging area will be made.

Location Conference Hall, C-MMACS New Bldg.
Contact Krishna Mohan
Speaker: Anil K. Singh, Head (retired), Materials Science Division, NAL, Bangalore

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