Point defects and high-temperature creep of non-stoichiometric NaCl-type oxide single crystals I. NiO

Abstract
Creep of NiO single crystals has been investigated by compression along 〈100〉 in the temperature range 0·6T m to 0·8T m, for stresses from 25 to 120 MPa and oxygen partial pressures pO2 from 10−5 to 0·2 atm. The data are analysed using the equation for recovery-controlled creep. The stress exponent decreases from a value of 12 to low temperature to 7 at high temperature; the activation energy is in the range 5·4 to 8·5 eV and the pO2 exponent varies from 0 to -0·17. The rate-controlling mechanism exhibits a change at, about 0·7T m which can be interpreted in two different ways. Oxygen diffusion plays a dominant role in the rate-controlling mechanism of creep, and occurs via a vacancy mechanism.