Critical Behavior at a Valence Instability

The isomorphic phase transition in the system Ce_1-xThₓ, which is characterized by a delocalization of the $4f$ electron and a concomitant volume change, has been studied through measurements of the density and resitivity. For samples near the critical composition (x0.264) derivatives of these quantities diverge with mean-field exponents. Such mean-field behavior implies a long-force range, and suggests that electroelastic coupling dominates the critical behavior.