Regularity of change in crystal lattice parameters in the series of hexavalent actinide trinitrates

Compounds of the type of MXO2(NO3)3, where M=K, Rb, Cs, and NH4; X=U, NP, and Pu, belonging to the hexagonal symmetry group with space groups R3C, were investigated by x-ray diffraction study (by the powder method). For the indicated compounds, with increasing number of the actinide element with a constant extrasphere cation, a regular decrease in the parameter a and an increase in the parameter c of the hexagonal cell were established. An analysis of these variations with a consideration of the crystal structure of the trinitrates permits us to conclude that in this case the X-O interatomic distance in the XO22+ group increases, while the X-O(NO3) distance decreases