Local atomic structure in (Zr1−xUx)N

Abstract (Zr1 − xUx)N solid solutions were prepared for EXAFS measurements by a sol–gel route combined with infiltration and carbothermic reduction. The lattice parameter and the more distant coordination shells (Me2 and Me3) around the Zr and U atoms follow the Vegard law. In the first coordination shell, the U–N distance also follows the Vegard law. Though the Zr–N bond distance increases with the lattice expansion caused by increasing U content, it remains constant at 232–235 pm in U-rich (Zr1 − xUx)N (x > 0.6). The measurements indicate that U accommodates the lattice contraction with increasing Zr content, whereas Zr is able to expand its Zr–N bond only at lower U content. In the composition range of transmutation fuels, (Zr1 − xUx)N is homogeneous at the local atomic scale.