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

Abstract

Magnesiowustite, (Mg0.08Fe0.88)O, and wustite, Fe0.94O, 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 { $$\left\{ {10\bar 14} \right\}$$ }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 { $${10{\bar{1}}4}$$ }r and { $${11{\bar{2}}0}$$ }r, and (0001)r and { $${10{\bar{1}}1}$$ }r, respectively, in the rhombohedral phase. The { $${11{\bar{2}}0}$$ }r planes preferentially aligned perpendicular to the compression direction while { $${10{\bar{1}}4}$$ }r oriented at a low angle to the compression direction. Similarly, { $${10{\bar{1}}1}$$ }r showed a slight preference to align more closely perpendicular to the compression direction than (0001)r. This variant selection may occur because the 〈 $${10{\bar{1}}4}$$ 〉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 { $${10{\bar{1}}4}$$ }〈 $${1{\bar{2}}10}$$ 〉r and { $${11{\bar{2}}0}$$ }〈 $${{\bar{1}}101}$$ 〉r slip and slightly less active { $${10{\bar{1}}1}$$ }〈 $${{\bar{1}}2{\bar{1}}0}$$ 〉r slip, the observed texture pattern can be obtained.