THE STRUCTURE AND MAGNETIC-PROPERTIES OF PR(3)MO(7) WITH M=NB, TA, AND SB

The crystal structure of the fluorite-related praseodymium compounds with the composition Pr3MO7, M = Nb, Ta, and Sb, have been determined using Rietveld refinement from X-ray and neutron powder diffraction data at 293 and 4 K. The structure described is orthorhombic with space group Cmcm (No. 63). It is a superstructure of the cubic fluorite structure with unit cell parameters aorth ≈ 2ac, borth ≈ corth ≈ ac 2, as in La3NbO7. This structure consists of chains of corner linked MO6 octahedra parallel with the c-axis. The magnetic susceptibility was measured between 4 and 300 K. The compounds obey the Curie-Weiss law including a Van Vleck temperature independent term. Pr3SbO7 shows a small deviation from this law below 25 K. © 1994 Academic Press, Inc.