Pressure-induced metallization of the perovskite Sr3Fe2O7

Electrical, magnetic and structural properties of the antiferromagnetic sem iconductor Sr3Fe2O7 (Fe4+, d(4)) were probed by resistance, Mossbauer spect roscopy (MS) and X-ray diffraction (XRD) measurements up to P approximate t o 40 GPa using diamond-anvil cells. A sluggish pressure-induced insulator-m etal (IM) transition is observed with a clear incipient metallic state at P greater than or equal to 20 GPa. The Fe(IV) 3d magnetic moments remain una ltered across the transition as deduced from MS, and XRD studies show no st ructural symmetry change up to 40 GPa. The results are consistent with carr ier delocalization due to p-p gap closure, e.g., ligand-to-ligand charge tr ansfer that does not involve the d-states and structural symmetry changes. A mechanism to account for the IM transition in the strontium ferrates is d iscussed.