Negative thermal expansion in thiospinel LiGaCr₄S₈

The thiospinel LiGaCr₄S₈ has been synthesized using solid state synthesis. X-ray diffraction, neutron diffraction, magnetic susceptibility and heat capacity measurements were carried out to study the physical and magnetic properties. The crystal structure of LiGaCr₄S₈ is derived from the well-known spinel structure, AB₂X₄, where Li and Ga occupy alternating A sites. The inequivalent cation ordering in A-sites leads to a reduction in the symmetry and the development of a breathing pyrochlore lattice with an alternating array of larger and smaller Cr₄ tetrahedra. Negative thermal expansion is observed between 111 and 11 K. No distortion from cubic symmetry was detected, however anomalies in the magnetic properties are observed corresponding to the region of negative thermal expansion. In particular, the magnetic susceptibility deviates from Curie-Weiss behavior coincident with the onset of negative thermal expansion. Whereas the recovery of normal thermal expansion is accompanied by the appearance of a broad peak in the magnetic susceptibility. Taken together, these results suggest strong magnetoelastic coupling in LiGaCr₄S₈.