Crystallographic preferred orientation in wüstite (FeO) through the cubic-to-rhombohedral phase transition

摘要

Magnesiowüstite, (Mg _(0. 08)Fe _(0. 88))O, and wüstite, Fe _(0. 94)O, were compressed to ~36 GPa at ambient temperature in the diamond anvil cell (DAC) at the Advanced Light Source. X-ray diffraction patterns were taken in situ in radial geometry in order to study the evolution of crystallographic preferred orientation through the cubic-to-rhombohedral phase transition. Under uniaxial stress in the DAC, {100} _c planes aligned perpendicular to the compression direction. The {100} _c in cubic became {0112} _r in rhombohedral and remained aligned perpendicular to the compression direction. However, the {101} _c and {111} _c planes in the cubic phase split into {1014} _r and {1120} _r, and (0001) _r and {1011} _r, respectively, in the rhombohedral phase. The {1120} _r planes preferentially aligned perpendicular to the compression direction while {1014} _r oriented at a low angle to the compression direction. Similarly, {1011} _r showed a slight preference to align more closely perpendicular to the compression direction than (0001) _r. This variant selection may occur because the 〈1014〉 _r and [0001] _r directions are the softer of the two sets of directions. The rhombohedral texture distortion may also be due to subsequent deformation. Indeed, polycrystal plasticity simulations indicate that for preferred {1014}〈1210〉 _r and {1120}〈1101〉 _r slip and slightly less active {1011}〈1210〉 _r slip, the observed texture pattern can be obtained.