Non-Vegard behavior of theUxLa1−xSsystem

We report extended x-ray-absorption fine structure measurements performed at the La K edge and the U L I I I edge of It samples in the U x La 1 - x S system. All samples have the simple NaCI fcc crystal structure. The measurements reveal a complex local variation of the first- (NN) and second-neighbor (NNN) distances. The La-S distances d L a S are systematically larger than the U-S distances d U S and almost concentration independent for x≤0.5. Around this concentration d L a S starts to decrease linearly with x. The study of the second-neighbor distances confirms a non-Vegard behavior of the lattice parameter evolution with La substitution. Near x ∼0.5 the static disorder in the solid solution strongly increases.