Variable Temperature Crystal Structure of Cu<sub>4</sub>TiTe<sub>4</sub>

Lakshan, Achintya; Petřı́ček, V.; Jana, Partha P.

doi:10.1002/ejic.202300219

Cited by 2 publications

(2 citation statements)

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“…37,38 The Te-variant also contains a similar Cu-disorder at a relatively higher temperature. 39,40 Due to the inhomogeneity of the powdered sample, the transport properties of the Te-analogue were not explored so far. 39 However, preliminary measurements for Cu 4 TiSe 4 indicate an ultralow thermal conductivity at room temperature.…”

Section: ■ Introductionmentioning

confidence: 99%

“…The physical properties of this compound were unknown until Hagiwara et al recently measured the thermal conductivity of Cu 4 TiS 4 to be ∼1.4 Wm –1 K –1 at 300 K . Interestingly, the selenium analogue (Cu 4 TiSe 4 ) is not isostructural to Cu 4 TiS 4 , the room-temperature structure can be represented by a small cubic cell ( a = 5.6418(2) Å; space group P 4̅3 m ) with the positional disorder at two Cu-sites. , The Te-variant also contains a similar Cu-disorder at a relatively higher temperature. , Due to the inhomogeneity of the powdered sample, the transport properties of the Te-analogue were not explored so far . However, preliminary measurements for Cu 4 TiSe 4 indicate an ultralow thermal conductivity at room temperature .…”

Section: Introductionmentioning

confidence: 99%

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Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Lakshan,

Koley,

Buxi

et al. 2024

Chem. Mater.

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Copper-transition-metal chalcogenides can offer low-cost and environmentally benign solutions to trap heat and heat to electric energy conversion. In this report, we present the synthesis and characterization of Cu–Ti-based mixed chalcogenides, Cu4TiSe4–x S x (x = 0–4). At room temperature, Cu4TiSe4 adopts a sulvanite-type cubic structure (P4̅3m), whereas Cu4TiS4 crystallizes in a body-centered tetragonal space group (I4̅2m), where the lattice parameter is doubled along the c-direction w.r.t. the sulvanite. The structure of the S-analogue is completely ordered, while the Se-analogue hosts positional disorder distributed over two Cu-sites (1a and 4e Wyckoff sites). A systematic investigation of a series of compositions of Cu4TiSe4–x S x (0 ≤ x ≤ 4) indicates that S insertion in the Cu4TiSe4–x S x boosts the disordered 4e site to coalesce into the 1a site. Up to x ≈ 2.6, Cu4TiSe4–x S x forms the cubic phase similar to Cu4TiSe4, whereas, for x ≥ 3.5, the pure tetragonal phase related to Cu4TiS4 appears. Herein, the cubic-to-tetragonal phase transformation is rationalized by theoretical calculations. Thermal conductivity measurements show a significant increase in the lattice thermal conductivity (κL) values from the cubic (0.3–0.47 Wm–1 K–1) to the tetragonal (above 0.7 Wm–1 K–1) phases. Phonon band structure and phonon density of state calculations suggest that both Cu and Se atoms are responsible for the anharmonic scattering of the acoustic phonons in the Se-rich cubic phase, whereas Cu atoms primarily contribute to this scattering process in the S-rich tetragonal phase.

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Lakshan,

Koley,

Buxi

et al. 2024

Chem. Mater.

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Key Role of Positional Disorder and Soft Structural Framework for Lowering the Thermal Conductivity of Quaternary Ag_1–xCu_3+xTiSe₄ (0 ≤ x ≤ 0.8) System to an Ultralow Limit

Lakshan,

Buxi,

Acharyya

et al. 2024

Chem. Mater.

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Low thermal conductive semiconductors have attracted huge attention for heat management and heat harvesting applications. Although the weak chemical bonding in the Cu/Agbased chalcogenides is promising in suppressing heat transport, their quaternary analogs remain less explored. Here, we report on a comparative study of the crystal structure and thermal conductivity of various Ag-containing variants of Cu 4 TiSe 4 , i.e., Ag 1−x Cu 3+x TiSe 4 (x = 0−0.8) samples. Analysis of the crystal structure, phase transition, and temperature-dependent lattice thermal conductivity (κ L ) of pristine AgCu 3 TiSe 4 and Ag 1−x Cu 3+x TiSe 4 have been carried out both experimentally and theoretically. The cubic crystal structure (space group P4̅ 3m) of these Ag variants is identical to that of Cu 4 TiSe 4 or Cu 4 TiTe 4 , where a positionally disordered Cu sublattice is either replaced by Ag (for AgCu 3 TiSe 4 ) or by Ag/Cu substructure (for Ag 1−x Cu 3+x TiSe 4 ). Upon cooling, the symmetry reduction to a rhombohedral (space group R3m) structure is attributed to the partial ordering of the positionally disordered Ag. The proposed structural models at different temperatures have been further analyzed using the Maximum Entropy Method (MEM). X-ray photoelectron spectroscopy measurement suggests that the parent compound forms a charge-precise (Ag + )(Cu + ) 3 (Ti 4+ )(Se 2− ) 4 chemical formula. Interestingly, the lattice thermal conductivity of the Ag 1−x Cu 3+x TiSe 4 samples remains very low, with values varying in the range of ∼0.65−0.24 W m −1 K −1 between 293 and 623 K. Density Functional Theory (DFT) calculation shows the presence of antibonding states of Cu(3d)/Ag(4d)−Se(4p) below the Fermi level (E F ), providing softness to the lattice of AgCu 3 TiSe 4 . In addition, the positional disordered site plays a crucial role in further softening the framework and provides large lattice anharmonicity. The calculated phonon dispersions evidence the presence of several soft optical phonon modes at ca. 25 cm −1 , originating from the atomic vibrations of Ag, Cu, and Se. Further confirmation of these phonon modes is obtained from the low-temperature heat capacity study. The low-lying optical phonon modes in AgCu 3 TiSe 4 are mainly caused by the presence of a soft lattice framework, positional disorder and associated rattling-like vibrations of Ag + /Cu + ions. Their strong interaction with the heat-carrying acoustic phonon modes is key ingredient that explains the very low κ L .

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Variable Temperature Crystal Structure of Cu₄TiTe₄

Cited by 2 publications

References 31 publications

Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Key Role of Positional Disorder and Soft Structural Framework for Lowering the Thermal Conductivity of Quaternary Ag_1–xCu_3+xTiSe₄ (0 ≤ x ≤ 0.8) System to an Ultralow Limit

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Variable Temperature Crystal Structure of Cu4TiTe4

Cited by 2 publications

References 31 publications

Disorder-Mediated Structural Transformation in the Cu4TiSe4–xSx (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Disorder-Mediated Structural Transformation in the Cu4TiSe4–xSx (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Key Role of Positional Disorder and Soft Structural Framework for Lowering the Thermal Conductivity of Quaternary Ag1–xCu3+xTiSe4 (0 ≤ x ≤ 0.8) System to an Ultralow Limit

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Variable Temperature Crystal Structure of Cu₄TiTe₄

Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Disorder-Mediated Structural Transformation in the Cu₄TiSe_4–xS_x (0 ≤ x ≤ 4) System and Its Effects on the Thermal Transport Property

Key Role of Positional Disorder and Soft Structural Framework for Lowering the Thermal Conductivity of Quaternary Ag_1–xCu_3+xTiSe₄ (0 ≤ x ≤ 0.8) System to an Ultralow Limit