Abstract
A thorough structural exploration has been made on the quasi-one-dimensional S = 1/2 compound Li 2 Cu 2 O(SO 4) 2 by neutron and synchrotron x-ray diffraction. It reveals the occurrence of a structural transition at 125 K, characterized by a lowering of symmetry from P 4 2 /m to P ¯ 1, which is possibly driven by an exchange striction mechanism. This transition involves a dimerization of some Cu in the edge-sharing tetrahedral Cu chains. A symmetry mode analysis indicates that one representation, 3 + 4 + , dominates the structural transition. Interestingly, no intermediate structure with P 112/m symmetry is observed experimentally. Lastly, temperature dependent magnetic susceptibility measurements and neutron diffraction reveal that the magnetic ground state of this compound is a spin-singlet with a spin gap, characterized by the absence of long-range magnetic order down to 1.7 K.