The lattice stiffening transition in UO single crystals.

The effective Debye temperatures ([Formula: see text]) of the surface region of UO single crystals, prepared by the hydrothermal synthesis technique, were obtained from temperature-dependent x-ray photoemission in the temperature range of 300 K-623 K. A lattice stiffening transition, characterized by different regions of different effective Debye temperature, 500  ±  59 K below 475 K and 165  ±  21 K above 475 K is identified. A comparison of the temperature dependence of the effective UO Debye temperature, with the changes in the lattice expansion coefficient for UO, support strong lattice-phonon interaction arising from the Jahn-Teller distortion.