Investigation of the Electronic Structure ofα′-Cerium by Angular-Correlation Studies of Positron-Annihilation Radiation

The electronic structures of the $\gamma , \alpha$, and ${\alpha }^{\prime }$ phases of cerium metal were investigated by measurement of the angular correlation of positron-annihilation radiation at pressures up to 90 kbar. The observed increase in the width of the angular correlation with increasing pressure was small and consistent with the assumption that the number of free electrons per atom is essentially the same, presumably three, in all three phases. The changes in width were much smaller than predicted by the promotional model which assumes that the $4f$ electron is promoted to the conduction band as cerium is compressed. It is therefore concluded that the promotional model does not provide a satisfactory explanation of the high-pressure behavior of cerium metal.