EXPERIMENTAL CONFIRMATION OF A P-P INTRABAND GAP IN SR2FEO4

The electrical-transport, magnetic, and structural properties of the a ntiferromagnetic semiconductor Sr2FeO4(Fe4+,d(4)) have been probed by resistance, Fe-57 Mossbauer spectroscopy, and x-ray-diffraction measur ements to similar to 30 GPa in a diamond-anvil cell. The pertinent res ults of this work are that a semiconductor-metal transition occurs at P(C)similar to 18(1) GPa, while the Fe(IV) 3d magnetic moments remain unaltered across the transition. To the highest pressure of 30 GPa, th e relative volume of the unit cell decreases to V/V(0)similar to 0.82, with no structural symmetry modification of the K2NiF4-type unit cell . At and above P-C, a magnetic hyperfine spectrum comprised of a singl e component with a non-negligible quadrupole interaction is evident be low spin-ordering temperatures T<T-N. No drastic or discontinuous chan ge occurs in both the hyperfine field (B-hf = 23 T) and isomer shift a t pressures encompassing P-C, suggesting that the Fe-3d electronic sta te is unchanged upon metallization. This is considered compelling expe rimental evidence for closure of a p-p gap within the ligand band mani fold, and therefore is the mechanism responsible for the onset of a me tallic state. [S0163-1829(98)06540-0].