Synthesis, Characterization, and Electrochemistry of Layered Chalcogenides LiCuCh (Ch = Se, Te)

Two novel compounds, LiCuCh (Ch = Se or Te), were synthesized by direct reaction between elements in closed ampules inside corundum crucibles. Both compounds are highly air-sensitive and possess an anti-PbClF crystal structure, which contains CuCh layer analogues to the Fe[As/Se] layers in Fe-based superconductors. In electrochemical battery cells, Li can be almost completely extracted from LiCuSe, but the reverse reaction is only partly successful and Li2Se and Cu2-xSe are formed instead. LiCuSe exhibits a temperature independent and slightly positive magnetic susceptibility. From Li-7 NMR measurements, the activation energy of the Li ion diffusion process is about 0.5 eV but is slightly lower for LiCuTe as compared to LiCuSe. Also, the small and almost temperature independent NMR shifts of the Li-7 nucleus indicate the absence of Pauli paramagnetism in these compounds, consistent with a 3d(10) full valence state of the Cu ions.