A zone-axis synchrotron diffraction study of complex and inhomogeneous Fe 1−x O thin single crystal under pressure is presented in this letter. Using this method, four phases are observed to coexist in a single crystal of Fe 1−x O at 35 GPa in diamond-anvil cells. One phase has cubic symmetry, whereas the other three phases have not been reported previously and can be interpreted as either orthorhombic or monoclinic. The discovery of multiple phases existing in Fe 1−x O indicates that

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... inhomogeneity of the sample can be induced under high pressure, a result that has important implications for the high P-T behavior of this complex material. Such information is not available using conventional diffraction techniques.