Zirconia is a brittle ceramic whose usefulness is negated by phase transformations which are accompanied by strains and the consequent stresses lead to cracking. The addition of MgO stabilises the high temperature phases. Transformation is triggered by an applied stress, so that crack tips are closed by the dilatational strains. This “transformation toughening” makes for a useful engineering material. There are two, little-understood features of the material. First, the martensitic transformation in Mg-PSZ is time-dependent, causing creep under a constant stress. Second, when the applied stress is removed, the creep reverses. These phenomena occur under both tensile and compressive stresses, but at very different magnitudes. A model has been proposed that explains some aspects of this behaviour and this project aims to test it and to further understand these features.