Cu4TiTe4: Synthesis, Crystal Structure, and Chemical Bonding.

Abstract

A new compound Cu4TiTe4 in the Cu-Ti-Te ternary system is prepared using high-temperature solid-state synthesis and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray spectroscopy. The average structure of Cu4TiTe4 crystallizes in the cubic space group P4̅3m (cP9; a = 5.9484(1) Å) and adopts the Cu4TiSe4 structure type. Like Cu4TiSe4, it shows positional disorder in one of the two Cu sites. The three-dimensional structure of Cu4TiTe4 is viewed as a cubic close-packed (ccp) array of Te, where half of the tetrahedral holes are orderly occupied by three Cu and one Ti and the disordered Cu atoms effectively occupied 1/4 of the octahedral holes. The calculated density of states (DOS) discerns that the compound is a narrow-bandgap semiconductor, and the crystal orbital Hamilton population (COHP) analysis shows that though the individual Cu-Te short contact is relatively weak compared to the Ti-Te contact, Cu-Te bonds largely contribute toward the overall stability. Due to the unique atomic arrangements, some Te atoms in the unit cell have unsaturated coordination, which presents 5s2 lone pairs on the Te atoms. This has been confirmed by the density of states (DOS) and electron localization function (ELF) calculations.