Invar effect in Pu-Ga alloys

We show that the anomalous thermal expansion behavior of Pu-Ga alloys can be explained by an invar effect, which is modeled by assuming the thermal transfer of Pu atoms from a lower-energy, higher-volume δ1 state to a higher-energy, lowervolume δ2 state. From a fit to the available neutron diffraction data on the lattice constants of Pu-Ga alloys, the energy separation of these states is found from thermal expansion data to be 1400K. The invar model enables a precise evaluation of the coefficient of thermal expansion and of the Grüneisen constant. The addition of Ga forces a stabilization of the δ2 state and suppresses the negative thermal expansion. † E-mail: [email protected]