Original paper

X-ray diffraction, optical, and transmission electron microscopic studies of experimentally shock-loaded periclase (MgO)

Schneider, H.; Ashworth, J.R.

Neues Jahrbuch für Mineralogie - Abhandlungen Band 144 Heft 3 (1982), p. 231 - 253

18 references

published: Sep 1, 1982

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Single crystals of periclase were shock-loaded to 50, 95, 300, 380 and 600 kbar. The shock wave direction was parallel to one a axis, arbitrarily taken to be [001]. Powder X-ray diffraction shows that the unit-cell dimension increased slightly in the high-pressure experiments. Split lines, in the 300 kbar and more heavily shocked material, indicate presence of both the expanded lattice and normal periclase. X-ray precession photographs of the reciprocal hOl, Okl and hkO planes are used to infer axes of rotational deformation. At 50 kbar, only one a axis, perpendicular to the shock direction, acted as a rotation axis. At 300 and 600 kbar, both such axes, [100] and [010], did so. Rotation about [001] is inferred in one 300 kbar specimen and is more prominent at 600 kbar. Optically observed birefringent bands and planar elements, parallel to {110} planes, correlate in orientation with dislocation slip bands observed in TEM which are believed to be responsible for the optical features. Cracks on {100} planes are best developed at 50 kbar. A {100} lamellar structure is observed by TEM in 300 and 600 kbar specimens and is associated with rotation of the lattice, approximately about (100) axes, and thus should be related to the streaking in single-crystal X-ray diffraction. In the 600 kbar specimen, a fine structure of blocky domains predominates over dislocations. Shock deformation of periclase is strongly anisotropic and heterogeneous; anisotropic in the sense that deformation systems which might be expected to be equivalent by symmetry are not active, and heterogeneous in the sense that the extent of deformation varies greatly within small volumes of crystal. This latter effect may explain the coexistence of normal and expanded lattices, the metastable expanded form being preserved in areas of high defect density.


Experimental studyshock waveshigh pressure (50-600 kb)periclaseX-ray powder diffractionsingle crystal methodTEM-datacell dimensionsbirefringencedeformation (planar)fracturingmicrocrackslattice (rotation) crystal dislocationslamellaedefects (domain structure)heterogeneityanisotropy