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

Two novel compounds, LiCu Ch ( 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 Cu Ch 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 Cu_{2- x}Se are formed instead. LiCuSe exhibits a temperature independent and slightly positive magnetic susceptibility. From ⁷Li 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 ⁷Li nucleus indicate the absence of Pauli paramagnetism in these compounds, consistent with a 3 d¹⁰ full valence state of the Cu ions.