Monoclinic distortion and magnetic transitions in FeO under pressure and temperature.

Fe_1-xO, although chemically simple, possesses a complex structural and magnetic phase diagram. The crystal structures of Fe_1-xO and its magnetic properties at extreme conditions are still a matter of debate. Here, we performed a systematic investigation on Fe_0.94O up to 94 GPa and 1700 K using synchrotron X-ray diffraction and synchrotron Mössbauer source spectroscopy. We observe a transition of Fe_0.94O to the monoclinic phases above 40 GPa and at high temperatures and use the group theory analysis of the observed phases to discuss their properties and their relation to the ambient pressure phases. The Mössbauer spectra of the rhombohedral and the room temperature monoclinic phase contain a component attributed to Fe^2.5+, caused by the electron exchange between the Fe³⁺ defect and neighboring Fe²⁺ atoms. Our results present a structural and magnetic transitional pressure-temperature diagram of Fe_1-xO and show the complex physicochemical properties of simple Fe_1-xO binary oxide under extreme conditions. This work concerns a systematic study of Fe_1-xO employing complementary methods of powder and single-crystal X-ray diffraction and synchrotron Mössbauer source spectroscopy up to 94 GPa and 1700 K. It presents a structural and magnetic transitional pressure-temperature diagram of Fe_1-xO and demonstrates the complex physicochemical properties of simple Fe_1-xO binary oxide under extreme conditions. [ABSTRACT FROM AUTHOR]