Deformation of Cube‐Oriented MgO Crystals Under Pressure

Plastic deformation in MgO crystals compressed parallel to a cube axis was studied under confining pressures up to 10 kbars at room temperature. The specimens were jacketed either in thick commercial rubber or in very thin latex. There were marked differences from behavior at atmospheric pressure, especially when thick rubber jackets were used at the higher pressures, at which they were in the glassy state; the stress‐strain curves of the MgO then tended to be abnormally high, and there was more marked activity of obliquely oriented slip planes. These effects can be attributed to additional stresses arising from the constraint of the rubber jackets, which can also give rise to kink bands at the longitudinal edges of the specimens. Such effects demonstrate the more effective hardening that arises from the interaction and intersection of the dislocations on oblique {110} slip planes and have important implications for the deformation of grains in the constrained conditions within polycrystalline specimens.