Abstract
The phase transitions of the strongly correlated tetrahedral -cluster compound have been studied by low-temperature powder x-ray diffraction, magnetic susceptibility, and specific heat measurements. The crystal structure is cubic at room temperature (space group ) and transforms to orthorhombic (space group ) at . A Jahn–Teller distortion reduces the symmetry of the -cluster from to . The second transition at 18 K is the onset of antiferromagnetic ordering without symmetry change but with a certain increase in the distortion. The latter reflects a strong magnetoelastic coupling at . Specific heat anomalies at 30 and 18 K confirm the two phase transitions.
- Received 14 March 2008
DOI:https://doi.org/10.1103/PhysRevB.77.212102
©2008 American Physical Society