Cubic Stuffed-Diamond Semiconductors LiCu3TiQ4 (Q = S, Se, and Te).

Lithium chalcogenides have been understudied, owing to the difficulty in managing the chemical reactivity of lithium. These materials are of interest as potential ion conductors and thermal neutron detectors. In this study, we describe three new cubic lithium copper chalcotitanates that crystallize in the P4̅3m space group. LiCu3TiS4, a = 5.5064(6) Å, and LiCu3TiSe4, a = 5.7122(7) Å, represent two members of a new stuffed diamond-type crystal structure, while LiCu3TiTe4, a = 5.9830(7) Å crystallized into a similar structure exhibiting lithium and copper mixed occupancy. These structures can be understood as hybrids of the zinc-blende and sulvanite structure types. In situ powder X-ray diffraction was utilized to construct a "panoramic" reaction map for the preparation of LiCu3TiTe4, facilitating the design of a rational synthesis and uncovering three new transient phases. LiCu3TiS4 and LiCu3TiSe4 are thermally stable up to 1000 °C under vacuum, while LiCu3TiTe4 partially decomposes when slowly cooled to 400 °C. Density functional theory calculations suggest that these compounds are indirect band gap semiconductors. The measured work functions are 4.77(5), 4.56(5), and 4.69(5) eV, and the measured band gaps are 2.23(5), 1.86(5), and 1.34(5) eV for the S, Se, and Te analogues, respectively.