STRUCTURE, MAGNETISM AND ABSORPTION-SPECTRA OF SOME ORTHOURANATES AND ORTHONEPTUNATES

The crystallographic and spectroscopic properties as well as the magnetic susceptibilities of Sr3UO6, Ca3UO6, Sr3NpO6 and Ca3NpO6 were determined. Data for the uranates are in agreement with structures proposed earlier. From X-ray powder patterns and IR arguments the neptunates seem to exhibit a somewhat less distorted lattice. Electronic spectra indicate only slightly distorted NpO6 octahedra. Magnetic susceptibilities are comparable with data from other 5f0 and 5f1 systems respectively. The absence of magnetic transitions in the neptunates is explained by the unavailability of An-O-An chains in the lattice, thus suppressing superexchange via oxygen ions.