Monoclinic Gd2O3, when submitted to thermal and mechanical stresses, does not.behave in a brittle manner. During the application of such stresses, twinned grains appear, especially on the surface of the samples; there is also the evolution of induced microcracks around the main crack. These two phenomena lead to the pseudo-plastic behaviour of the material. (C) 1998 Elsevier Science Limited. All rights reserved.