IN SEARCH OF A SYSTEMATICS FOR THE VISCOSITY OF PEROVSKITES - CREEP OF POTASSIUM TANTALATE AND NIOBATE

With a view to gathering information on the high-temperature creep of crystals with perovskite structure, the creep behavior of single crystals of KTaO3 and KNbO3 has been investigated and the characteristic dislocation structures have been observed by transmission electron microscopy. At temperatures between 0.87 and 0.99 Tm, KTaO3 deforms by Newtonian Harper-Dorn creep (n = 1) with an activation energy Q = 292 ± 39 kJ mol-1, slip occurs mostly on {100} planes and the dislocations are mostly edge with Burgers vector 〈001〉, they easily expand in their climb planes and there probably is some pure climb strain. The results are compared with those previously obtained in the case of BaTiO3. It is found that perovskites do not constitute an isomechanical group and that the distortions of the lattice may be important in determining the dislocation core structures and the creep mechanisms. © 1990.