Cu₄TiTe₄: Synthesis, Crystal Structure, and Chemical Bonding

Abstract

A new compound Cu 4 TiTe 4 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 Cu 4 TiTe 4 crystallizes in the cubic space group P4̅ 3m (cP9; a = 5.9484(1) Å) and adopts the Cu 4 TiSe 4 structure type. Like Cu 4 TiSe 4 , it shows positional disorder in one of the two Cu sites. The three-dimensional structure of Cu 4 TiTe 4 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 5s 2 lone pairs on the Te atoms. This has been confirmed by the density of states (DOS) and electron localization function (ELF) calculations.

Variable Temperature Crystal Structure of Cu4TiTe4

“…The average structure of Cu 4 TiTe 4 and the chemical bonding have been detailed in a recent article. [22] The average structure of Cu 4 TiTe 4 is found to be similar to the room temperature structure of Cu 4 TiSe 4 . Like Cu 4 TiSe 4 , the average structure of Cu 4 TiTe 4 crystallizes in the cubic crystal system and possesses occupational disorder in the Cu-sites although the occupancy at disordered Cu-sites differs from the Se-analogue.…”

“…At this stage, the disorder Cu‐sites were showing unexpected occupancies (∼48 % and ∼18 % respectively, which leads to a refined composition of Cu 4.348 TiTe 4 ) and no further improvement in the refinement results were observed. Furthermore, when the occupancies of these disorder Cu‐sites were fixed to 25 % (as was the case for the high temperature cubic structure [22] ), the refinement converged to a high R‐value. Hence, to check the possibility of twinning (by syngonic and metric merohedry) the low symmetry space groups (corresponding to the subgroups of F $${\bar{4}}$$ 3 m ) were used to solve the data.…”

“…Structure solutions and structure refinements were carried out in the Jana2006 program [25,26] . The average structure was solved in the P $${\bar{4}}$$ 3 m space group ( a ≈5.9 Å) and recently reported [22] . The average structural model was used as an initial model for the refinement of the single‐crystal X‐ray diffraction data collected for the single crystal at T =320, 330, and 400 K. The reflection data collected at T =298 K suggested that the observed diffraction pattern corresponded to F ‐centred cubic cell with a ≈11.887 Å.…”

“…Te‐analogue Cu 4 TiTe 4 is recently been discovered in our group. The average structure of Cu 4 TiTe 4 and the chemical bonding have been detailed in a recent article [22] . The average structure of Cu 4 TiTe 4 is found to be similar to the room temperature structure of Cu 4 TiSe 4 .…”

“…Crystal structure of Cu 4 TiTe 4 between 320-400 K is cubic and resembles the average structure of Cu 4 TiTe 4 , reported in the previous work. [22] It contains four crystallographic independent positions, two Cu (3c and 4e) and one Ti (1b) and one Te (4e). The Cu-4e site (site occupancy factor, SOF � 0.25) possesses occupational disorder [Table S4].…”