Fig. 1

Crystal structure and image of the Fe₄O₅ crystal. a Orthorhombic crystal structure of Fe₄O₅ at ambient conditions showing the different crystallographic positions for iron atoms (Fe1, Fe2, and Fe3) in different colors. The bond valence sum values are indicated near the cations. b Image of a single crystal of Fe₄O₅ taken through one diamond window. A rhenium gasket of about 40 µm thickness with a circular hole of about 150 µm diameter drilled in its central part is bridged between the two opposing diamond anvils. The light background color of the central hole is due to light passing through the underlying diamond anvil. The central hole (working area) accommodates the Fe₄O₅ single crystal (in the center) and two small pressure markers, Au and ruby, located on the left and right sides of the crystal, respectively. The central hole is filled with a transparent neon pressure-transmitting medium. The scale bar inside the central hole corresponds to 100 µm