valence transition

valence transition

[′vā·ləns tran‚zish·ən]
(physical chemistry)
A change in the electronic occupation of the 4 f or 5 f orbitals of the rare-earth or actinide atoms in certain substances at a certain temperature, pressure, or composition.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.