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A variable temperature single crystal X‐ray diffraction study of the ternary compound, Cu4TiTe4 is reported between 200–400 K. The temperature dependent study indicates the compound undergoes an order‐disorder phase transition at ∼320 K. Below the transition temperature, the phase that crystallizes in the primitive cubic space group P4‾ ${\bar{4}}$ 3 m with lattice parameter of a≈5.9 Å, transforms into the two‐fold superstructure. It is modeled as a fourfold twinned rhombohedral structure. The transition is reversible. To relate the phases, a group‐subgroup symmetry relations are established. Upon decreasing temperature, the atomic ordering is noticed in the occupationally disordered Cu‐sites of Cu4TiTe4. This characteristic structural rearrangement may have a significant impact on the electronic structure of Cu4TiTe4. Hence, the detailed structural characterization is supposed to be useful for further understanding of thermoelectric transport properties in the Cu4TiTe4. [ABSTRACT FROM AUTHOR]

A variable temperature single crystal X‐ray diffraction study of the ternary compound, Cu4TiTe4 is reported between 200–400 K. The temperature dependent study indicates the compound undergoes an order‐disorder phase transition at ∼320 K. Below the transition temperature, the phase that crystallizes in the primitive cubic space group P4‾ ${\bar{4}}$ 3 m with lattice parameter of a≈5.9 Å, transforms into the two‐fold superstructure. It is modeled as a fourfold twinned rhombohedral structure. The transition is reversible. To relate the phases, a group‐subgroup symmetry relations are established. Upon decreasing temperature, the atomic ordering is noticed in the occupationally disordered Cu‐sites of Cu4TiTe4. This characteristic structural rearrangement may have a significant impact on the electronic structure of Cu4TiTe4. Hence, the detailed structural characterization is supposed to be useful for further understanding of thermoelectric transport properties in the Cu4TiTe4. [ABSTRACT FROM AUTHOR]

The newly synthesized ultralow thermal conducting Cu4TiSe4 undergoes a temperature‐induced reversible structural phase transition at −92 °C. The room temperature structure exhibits cubic symmetry (space group P4‾ 3 m with lattice parameter a=5.6458(1) Å) and shows positional disorder in two Cu‐sites (4e and 1a Wyckoff sites). In this report, a structural study was carried out on the same sample by means of single‐crystal X‐ray diffraction data (nitrogen‐cryostat) collected at 131 K. At this temperature, Cu4TiSe4 crystallizes in rhombohedral symmetry, space group R3 m, with a=7.9538(5) Å and c=19.4828(17) Å. The low temperature structure is fourfold twinned. In the low temperature phase, copper atoms at 9b and 3a Wyckoff sites (originally 4e and 1a Wyckoff sites in the room temperature structure) order partially in comparison to room temperature structure. This temperature induced phase transition induce slight increase of the thermal conductivity of the material. [ABSTRACT FROM AUTHOR]

The newly synthesized ultralow thermal conducting Cu4TiSe4 undergoes a temperature‐induced reversible structural phase transition at −92 °C. The room temperature structure exhibits cubic symmetry (space group P4‾ 3 m with lattice parameter a=5.6458(1) Å) and shows positional disorder in two Cu‐sites (4e and 1a Wyckoff sites). In this report, a structural study was carried out on the same sample by means of single‐crystal X‐ray diffraction data (nitrogen‐cryostat) collected at 131 K. At this temperature, Cu4TiSe4 crystallizes in rhombohedral symmetry, space group R3 m, with a=7.9538(5) Å and c=19.4828(17) Å. The low temperature structure is fourfold twinned. In the low temperature phase, copper atoms at 9b and 3a Wyckoff sites (originally 4e and 1a Wyckoff sites in the room temperature structure) order partially in comparison to room temperature structure. This temperature induced phase transition induce slight increase of the thermal conductivity of the material. [ABSTRACT FROM AUTHOR]

Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu4TiSe4 are reported. Cu4TiSe4 is a unique example of a non‐toxic and low‐cost material that exhibits a lattice ultra‐low thermal conductivity of 0.19 Wm−1 K−1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (kL) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu4TiSe4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations. [ABSTRACT FROM AUTHOR]

Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu4TiSe4 are reported. Cu4TiSe4 is a unique example of a non‐toxic and low‐cost material that exhibits a lattice ultra‐low thermal conductivity of 0.19 Wm−1 K−1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (kL) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu4TiSe4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations. [ABSTRACT FROM AUTHOR]

Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu4TiSe4 are reported. Cu4TiSe4 is a unique example of a non‐toxic and low‐cost material that exhibits a lattice ultra‐low thermal conductivity of 0.19 Wm−1 K−1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (kL) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu4TiSe4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations. [ABSTRACT FROM AUTHOR]

Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu4TiSe4 are reported. Cu4TiSe4 is a unique example of a non‐toxic and low‐cost material that exhibits a lattice ultra‐low thermal conductivity of 0.19 Wm−1 K−1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (kL) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu4TiSe4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations. [ABSTRACT FROM AUTHOR]

This study explores the structure and stability of partly disordered sulfur-substituted Ni 5.74 InSe 2 ( I 4/ mmm , a = 3.6766(1) Å, c = 18.8178(10) Å, Z = 2). The structure of Ni 7- δ InSe 2- x S x ( x = 0.2, 0.36, 0.66, 0.80, 0.94) compounds is isotypic to their parent Ni 5.74 InSe 2 and can be viewed as alternating heterometallic Cu 3 Au-type ∞ 2 [ Ni 3 In ] slabs and defective Cu 2 Sb-type ∞ 2 [ Ni 4-δ (Se/S) 2 ] slabs along the [001]-axis. Similar to the parent Se-compound, the Ni- Ch ( Ch = chalcogen) fragment is non-stoichiometric and possesses a partially occupied Ni-site. It was observed that with sulfur insertion at the selenium site of Ni 5.74 InSe 2 , the interatomic distance between the partially occupied nickel and mixed (S/Se) sites decreases from ∼2.24 to ∼1.95 Å, and the occupancy of the disordered nickel site simultaneously increases. The limiting composition Ni 6.06 InSe 0.67 S 1.33 ( x = 1.33, δ = 0.94) is formed in the sulfur-rich region. Its average structure resembles the Ni 6 SnS 2 -type and has a similar motif to Ni 5.74 InSe 2 ; the only difference is that Cu 3 Au-type ∞ 2 [ Ni 3 In ] alternates with two types of Ni- Ch fragments (Cu 2 Sb or Li 2 O type units). By using first-principles electronic structure calculations, we explained the presence of partially disordered nickel sites in the Ni- Ch fragment and rationalized why the nickel site occupancy increases with sulfur insertion.

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 P 4̅3 m ( cP 9; 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.

Ultralow thermal conductivity draws great attention in a variety of fields of applications such as thermoelectrics and thermal barrier coatings. Herein, the crystal structure and transport properties of Cu 4 TiSe 4 are reported. Cu 4 TiSe 4 is a unique example of a non-toxic and low-cost material that exhibits a lattice ultra-low thermal conductivity of 0.19 Wm -1  K -1 at room temperature. The main contribution to the unusually low thermal conductivity is connected with the atomic lattice and its dynamics. This ultralow value of lattice thermal conductivity (k L ) can be attributed to the presence of the localized modes of Cu, which partially hybridize with the Se atoms, which in turn leads to avoidance of crossing of acoustic phonon modes that reach the zone boundary with a reduced frequency. Like a phonon glass electron crystal, Cu 4 TiSe 4 could also open a route to efficient thermoelectric materials, even, with chalcogenides of relatively high electrical resistivity and a large band gap, provided that their structures offer a sublattice with lightly bound cations., (© 2020 Wiley-VCH GmbH.)