Non-Vegard behavior of the UxLa1-xS system

We report extended x-ray-absorption fine structure measurements performed at the La K edge and the U LIII edge of 11 samples in the UxLa1-xS system. All samples have the simple NaCl fcc crystal structure. The measurements reveal a complex local variation of the first- (NN) and second-neighbor (NNN) distances. The La-S distances dLaS are systematically larger than the U-S distances dUS and almost concentration independent for x≤0.5. Around this concentration dLaS 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