Effect of Pressure on the Spectra of Transition Metal Ions in MgO and Al2O3

Abstract

The effect of pressure to 150 kbar has been measured on the spectra of several transition metal ions in MgO and Al2O3. In general, there is an increase in crystal field strength with increasing pressure. The inter-electronic repulsion parameter decreased slightly with increasing pressure indicating a small increase in covalency. For Al2O3, Dq shifts as (V0/V)5/3 indicating that the R−5 law holds, and the local compressibility is the same as the bulk compressibility. In MgO the shift is always more rapid than R−5, indicating local relaxation near the foreign ion. Above about 50 kbar there is a marked increase of trigonal distortion in Al2O3.