The polarized optical absorption spectrum of Cr2O3 in thin single‐crystal plates has been obtained at temperatures from 4.2°K upward. The crystal field at the Cr ions in Cr2O3 has been calculated in the same way as for Cr:Al2O3 since their crystal structures are very similar. The experimental results for Cr2O3 were used to derive empirical values for the quantities 〈r2〉 and 〈r4〉 which appear in the expressions for the cubic and trigonal fields of Cr2O3, and these were substituted into the expression for the trigonal field of Cr:Al2O3. The result is a calculated trigonal field much smaller than is observed. The Cr ion in Al2O3 may therefore be displaced from the Al position as was suggested in a previous study. The details of the Cr2O3 spectrum, particularly the lines, are illustrated and commented upon, but no detailed analysis is presented. The spectrum does show many evidences of exchange coupling, however.

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K. Wickersheim, private communication; also in the Report of the Magnetism Conference, November 1962.
4.
See, for example, the Dq values published by
H. A.
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10.
Wickersheim, working with an instrument of higher resolving power, finds that both the width and strength of lines originating in the ground state depend on temperature.
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