Superstructures and Superconductivity Linked with Pd Intercalation in Nb2PdxSe5

Single crystals of Nb2PdxSe5 have been grown covering a broad range of palladium stoichiometries from x = 0.68-0.95 (Pd2 occupancies of 0.36 and 0.90, respectively). Miscibility gaps in the Pd stoichiometry range are related to superstructures resulting from staged filling and ordering of the partially filled Pd atom site (Pd2, Wyckoff site 2a). For Pd2 near 1/2 occupancy, a superstructure based on an incommensurate occupation wave with modulation along the monoclinic b axis is identified. A superconducting dome is found for Pd2 occupancies above 0.58 with a maximum T-c for Pd2 occupancy of similar to 2/3. DFT calculations for the fully and 1/2-occupied Pd2 site show that Nb2PdxSe5 can be considered an intercalation compound for Pd2 occupancy above the minimum required for structural stability.