High Temperature Creep of Metal Oxides

Abstract

This chapter presents a comprehensive review of the creep technique used for the study of defect structure and diffusion in metal oxides, both single crystals and ceramics. At high temperatures, the creep rate is proportional to the diffusion coefficient of the slowest species in solid compounds, whatever deformation mechanisms are present (Nabarro viscous creep, recovery creep or pure climb creep). The creep rate dependence on deviation from stoichiometry can be determined from this diffusion. In the case of metal oxides, the departure from stoichiometry is controlled by the oxygen activity which usually is identified with oxygen partial pressure, p O 2 . The p O 2 dependence of the creep rate provides direct information about the nature of minority point defects. On the other hand, studies of the temperature dependency of the creep rate inform us about the activation energy of the diffusion coefficient.This review focuses primarily on the creep behavior of transition metal oxides such as Ni 1Ày O, Co 1Ày O, Fe 1Ày O exhibiting disorder in metal sublattice, as well as ZrO 2Àx with majority defects in oxygen sublattice. The advantage of these studies is determination of both defect structure and diffusion coefficients of minority defects namely in oxygen sublattice in iron-triad oxides and in zirconium ZrO 2 sublattice.