Thermal Signatures of the Kondo Volume Collapse in Cerium

X-ray diffraction measurements of cerium in the vicinity of the isostructural gamma-alpha transition have been performed with high precision and accuracy from room temperature to almost 800 K. The disputed location of the critical point has been found to occur at 1.5 +/- 0.1 GPa and 480 +/- 10 K. The data are well fit by the Kondo volume collapse model plus a quasiharmonic representation of the phonons. The resultant free energy is validated against data for the thermodynamic Gruneisen parameter and, beyond the dominant spin-fluctuation contribution, indicates a dramatic change in the lattice Gruneisen parameter across the transition.