The effect of pressure to 200 kbars has been measured on the Mouml;ssbauer resonance of57Fe in a sodium silicate and a sodium phosphate glass. In the silicate glass, the Fe(III) ion is in a tetrahedral site. The isomer shift goes through a maximum (i.e., a minimum in the electron density at the nucleus) with increasing pressure. This is interpreted in terms of competition between the decrease in shielding of the3selectrons by the3delectrons and changes in orbital occupation. The octahedral Fe(II) sites also show a combination of site compression, site distortion, and change in orbital occupation with pressure. Both Fe(III) and Fe(II) sites in phosphate glass are octahedral. Both in regard to change of isomer shift and change of quadrupole splitting, these sites behave qualitatively like those in crystalline FePO4and Fe3(PO4)2, which were previously studied. The Fe(III) ions tend to reduce to Fe(II) with pressure, just as occurs in a large number of crystalline ferric compounds.
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