Correlation between the structure and paramagnetic susceptibility of NdOF

The high-resolution X-ray powder diffraction patterns on the polycrystalline NdOF were measured at selected temperatures between 6 and 295 K. The hexagonal unit cell constants a and c first decrease as a function of temperature as anticipated down to ca. 50 K but then suddenly a increases and c decreases strongly, The cell volume remains constant, however. The compression of the lattice in the direction parallel to the c-axis is due to the high anisotropy of the NdOF lattice. The rigid NdO+ complex cation prevents the compression in the plane perpendicular to the c-axis and results in a slight dilatation in the plane. The experimental paramagnetic susceptibility measured between 3 and 850 K shows also an anomalous behavior around 50 K indicating that the structural changes influence the magnetic properties as well. The evolution of the paramagnetic susceptibility as a function of temperature was well simulated below 50 K by wave functions and energy level values obtained from inelastic neutron scattering measurements at 2.5 K. Above 50 K the simulation fails because of structural changes. The high anisotropy of the NdOF lattice was concluded to be responsible also for the anomalous behavior of the paramagnetic susceptibility as a function of temperature. (C) 1998 Elsevier Science S.A.