Dramatic technical progress seen over the past decade now allows the plastic properties of materials to be investigated under extreme pressure and temperature conditions. Coupling of high-pressure apparatuses with synchrotron radiation signiﬁcantly improves the quantiﬁcation of differential stress and specimen textures from X-ray diffraction data, as well as specimen strains and strain rates by radiography. This contribution brieﬂy reviews the recent developments in the ﬁeld and describes state-of-the-art extreme-pressure deformation devices and analytical techniques available today. The focus here is on apparatuses promoting deformation at pressures largely in excess of 3 GPa, namely the diamond anvil cell, the deformation-DIA apparatus and the rotational Drickamer apparatus, as well as on the methods used to carry out controlled deformation experiments while quantifying X-ray data in terms of materials rheological parameters. It is shown that these new techniques open the new ﬁeld of in situ investigation of materials rheology at extreme conditions, which already ﬁnds multiple fundamental applications in the understanding of the dynamics of Earth-like planet interior.
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