Unraveling the Nature of “H-phase” in the Deep Lower Mantle

It was proposed that Fe-bearing bridgmanite may undergo disproportionation under deep lower mantle conditions, forming an iron-depleted perovskite and an iron-rich silicate phase, referred to as the “H-phase”. If confirmed, this process would profoundly reshape our understanding of lower mantle mineralogy. However, the H-phase remains enigmatic more than a decade after its initial report: it has not been consistently reproduced by independent studies , and its crystal structure and composition remains unresolved. We have observed signs of “H-phase” in the water-bearing systems. In order to obtain reliable data for structural refinement and characterize iron oxidation state in the material, as well as to investigate the stability and potential geophysical roles of this iron oxyhydroxide in the lower mantle, we propose a systematic high-pressure study up to 150 GPa and 2500 K combining in situ synchrotron single crystal X-ray diffraction and Mössbauer (SMS) spectroscopy.