ABSTRACT
Strongly correlated electrons in layered perovskite structures have been the birthplace of high-temperature superconductivity, spin liquids, and quantum criticality. Specifically, the cuprate materials with layered structures made of corner-sharing square-planar CuO4 units have been intensely studied due to their Mott insulating ground state, which leads to high-temperature superconductivity upon doping. Identifying new compounds with similar lattice and electronic structures has become a challenge in solid-state chemistry. Here, we report the hydrothermal crystal growth of a new copper tellurite sulfate, Cu3(TeO4)(SO4)·H2O, a promising alternative to layered perovskites. The orthorhombic phase (space group Pnma) is made of corrugated layers of corner-sharing CuO4 square-planar units that are edge-shared with TeO4 units. The layers are linked by slabs of corner-sharing CuO4 and SO4. Using both the bond valence sum analysis and magnetization data, we find purely Cu2+ ions within the layers but a mixed valence of Cu2+/Cu+ between the layers. Cu3(TeO4)(SO4)·H2O undergoes an antiferromagnetic transition at TN = 67 K marked by a peak in the magnetic susceptibility. Upon further cooling, a spin-canting transition occurs at T* = 12 K, evidenced by a kink in the heat capacity. The spin-canting transition is explained on the basis of a J1-J2 model of magnetic interactions, which is consistent with the slightly different in-plane superexchange paths. We present Cu3(TeO4)(SO4)·H2O as a promising platform for the future doping and strain experiments that could tune the Mott insulating ground state into superconducting or spin liquid states.
