[en] Full text: Pure zirconia, ZrO₂, is not a useful material because phase transformations as it cools after processing at high temperature, are accompanied by dilatational and shear strains that lead to cracking. The addition of oxides such as MgO, stabilizes the high-temperature phases and the resultant “partially stabilized zirconia”, Mg-PSZ, is used in a variety of applications. There are two, little-understood features of the material. First, the transformation (which is martensitic) is time-dependent, causing creep under a constant stress (Fig. 1 [1]). Second, when the applied stress is removed, the creep strain reverses (Fig. 2 [2]). These effects occur under both tensile and compressive stresses, but at very different magnitudes. Partly motivated by a presentation at the International Conference on Martensitic Transformations (ICOMAT2017) held in Chicago in July, 2017 [3], we have studied Mg-PSZ in compression and simultaneously measured sample deformations (using strain gauges) and the accompanying microstructural changes using neutron diffraction at the ENGIN-X beamline on the ISIS, pulsed-neutron source at the Rutherford-Appleton Laboratory, Didcot, Oxfordshire, England. The advantage of such an experiment is that it provides simultaneous microstructural information both parallel to and perpendicular to the applied load on the compression sample. The results reveal two distinct stages of time-dependence, firstly, while the sample is under load and subsequently on the load removal. (author)