Diamond anvil cell investigation of lattice strains and preferred orientation in iron at high pressure and temperature.

High pressure and high temperature investigations on bcc and hcp iron have been performed using radial x-ray diffraction in the diamond anvil cell. The technique used in previous experiments (Mao et al. Nature, 1998, Wenk et al. Nature, 2000) have been further refined in order to use monochromatic x-ray beam and angular dispersive detectors. This allows us to investigate in great detail the variations in d-spacing and intensity of diffraction as a function of sample orientation and relate them to elasticity, strength, preferred orientation and texture in the sample. In this study, we investigate the lattice strains and the development of preferred orientation during compression in polycrystalline bcc-Fe and hcp-Fe between 0 and 35 GPa. The bcc phase if found to develop a mixed <100> and <111> fibers texture with compression. At the phase transition, the preferred orientation in hcp-Fe is inherited from the texture in bcc-Fe. With increasing pressure, we observe the development of the texture with dominating (0001) fiber component that was observed in previous experiments (Wenk et al. Nature, 2000). Double-sided laser heating of the sample at the highest pressure is then conducted in order to study the effect of temperature on preferred orientation. Analysis of the variation of the d-spacings with sample orientation can also be used to study the uniaxial stress component and elastic behavior under pressure and we apply it to our sample. This study proves the feasability of experimental investigation on elastic behavior, shear strength and deformation mechanisms under pressures and temperatures of the deep Earth. Mao, H.K., J. Shu, G. Shen, R.J. Hemley, B. Li, and A.K. Singh, Nature, 396, 741-743, 1998 Wenk, H.R., S. Matthies, R.J. Hemley, H.K. Mao, and J. Shu, Nature, 405, 1044-1047, 2000