M$sub 4$ $sub 5$ spectrum of Ce and the $gamma$--$alpha$ phase transition

Absolute absorption coefficients in the region of the M/sub 4/ and M/sub 5/ edges are presented for cerium in CeF/sub 3/, CeO/sub 2/, and in the metal. Strong line absorptions (3d yields 4f) occur to the low energy side of weak M/ sub 4/ and M/sub 5/ edges.'' At each edge'' the absorption passes through a weak broad peak attributed to transitions into a band of higher f states. The spectra of CeF/sub 3/ and the metal at room temperature are structurally similar but differ clearly from the quadrivalent oxide. A shift to higher energy is found for both absorption lines and edges in the sequence fluoride- oxide--metal at room temperature. On cooling the evaporated metal absorption foil ( gamma phase) to 77 deg K both M/sub 4/ and M/sub 5/ line profiles change into forms accurately resolvable into a combination of trivalent (CeF/sub 3/ like) and quadrivalent (CeO/sub 2/ like) curves, suitably displaced in energy, in the proportions 59% to 43%, respectively. This is interpreted as evidence for the transfer of localized 4f electrons from some of the 3+ ions of the gamma phase when the gamma -- alpha transformation occurs. The line structure exhibits hysteresis and reverts tomore » that of the original gamma phase after repeated cycling between 77 deg K and room temperature. The possibility of superlattice structure in alpha -cerium is discussed. (auth)« less