Creep of (Mg, Fe)O single crystals

Abstract

The creep behaviour of (Mg, Fe)O single crystals compressed along 〈1 0 0〉 has been investigated over the temperature range 1300 to 1500° C, at stresses between 20 and 70 MPa, for oxygen partial pressures between 10⁻⁴ and 10² Pa, and with iron concentrations between 70 and 11 900 p.p.m. Under these conditions, the dependence of the steady-state strain rate on stress, temperature, oxygen partial pressure, and iron concentration can be summarized by the flow law, $\dot \varepsilon = A\sigma ^{3.4} \left[ {Fe_{Mg} } \right]_{tot}^0 P_{O_2 }^0$exp (−445 kJ mol⁻¹/RT. These results suggest that the steadystate strain rate is controlled by dislocation climb with a jog velocity which is limited by lattice diffusion of oxygen by a vacancy pair mechanism. The activation energy for creep, 445 kJ mol⁻¹ is larger than that reported for self-diffusion of oxygen, 330 kJ mol⁻¹, because the formation energy for jogs is relatively large, 115 kJ mol⁻¹.