Abstract
Crystals of (R=Y,Er) have been grown, and their structures have been established by single-crystal x-ray diffraction. Both compounds crystallize in the structure type, with one-dimensional chains of vertex-sharing octahedra in the direction of the a axis. These octahedra show an unusual twofold distortion: The Ni-O distances to the two axial oxygen atoms are considerably shorter, 0.3 Å, than those to the four equatorial oxygens, and these oxygens are distorted from the right angles of a regular octahedron to 79.0(2)° or 77.7(6)°, respectively. As a result of this, Ni-O(axial)-Ni distances are very short, 3.76 and 3.75 Å for R=Y and Er, respectively. X-ray powder diffraction data and the results of magnetic measurements for both oxides are given. The structural features mentioned elucidate why ions in polycrystalline behave as a monodimensional system in which they become antiferromagnetically ordered below 300 K. Besides that, the ferromagnetic interactions that operate below 40 K can be due to tridimensional interchain interactions and/or the presence of ferromagnetic impurities. The estimated Néel temperature for , higher than that reported for , is explained by the promotion of the superexchange Ni-O-Ni interactions along the chains of flattened octahedra sharing corners. In both effects are masked by the strong paramagnetic signal of , and a maximum observed at 15.6 K for the susceptibility is attributed to tridimensional ordering of the cations.
- Received 12 June 1990
DOI:https://doi.org/10.1103/PhysRevB.42.7918
©1990 American Physical Society