Comments on Peierls‐distorted Indium Chains in In₄Se_3–x

Abstract

Nominal In4Se3–x with x = 0.65, derived from the prototype compound In4Se3, is a good thermoelectric material achieving a Z value of 1.48 at 705 K. This value is close to state of the art thermoelectric materials. In literature this special behavior is explained by a Peierls‐distortion or Charge Density Wave within the compound caused by the selenium deficit. While extensive thermoelectric studies for different compositions are reported in literature, a solid proof of the existence of selenium deficit samples is still missing. In this work we report about the synthesis, phase analyses, and temperature dependent single crystal determinations of In4Se3–x samples in order to clarify these structural features.

Origin of Low Thermal Conductivity in In4Se3

“…Therefore, a distortion leading to a superstructure is not expected for stoichiometric In 4 Se 3 . This is entirely consistent with the structural study of Osters and coworkers 33 , who found no evidence of a Peierls-distortion or a CDW in stoichiometric In 4 Se 3 . It is also noticeable that the frequency of the acoustic modes is very low, suggesting that the bonding is soft with a substantial number of low-frequency optical modes, close in energy to the acoustic modes.…”

“…The different nature of the bonding of In4 is reflected in its considerably larger atomic displacement parameter than those for the (In 3 ) 5+ cation found in the covalent layers, evident in single-crystal diffraction studies 33 . For instance, the atomic displacement parameter for In4 found by Osters and coworkers 33 is 60% larger than those in the (In 3 ) 5+ cation.…”

“…The low thermal conductivity of selenium-deficient In 4 Se 3−δ has been proposed that is the result of a charge density wave (CDW) induced by a quasi-one-dimensional lattice Peierls distortion . This, however, has been questioned by Osters and co-workers, who found that In 4 Se 3 behaves as a line phase and does not accommodate selenium deficiency. Instead, selenium-deficient samples were found to contain indium metal, while single-crystal X-ray diffraction data provide no evidence of a CDW .…”

“…The outstanding thermoelectric performance of In 4 Se 3 has been attributed to its low thermal conductivity, which is ~ 0.9 W•m -1 K -1 for the undoped polycrystalline material at room temperature 17,18,19,32 , while in doped and selenium-deficient samples, values as low as ~ 0.4 W•m -1 K -1 at 723 K can be reached 30,31 . This, however, has been questioned by Osters and co-workers 33 , who found that In 4 Se 3 behaves as a line phase and does not accommodate selenium deficiency. Instead, selenium-deficient 7 samples were found to contain indium metal 32 , while single-crystal X-ray diffraction data provide no evidence of a CDW 33 .…”

Structural and Thermoelectric Properties of Solid–Liquid In4Se3-In Composite

“…It indicates that possible deviation from stoichiometry is very small. This result is consistent with those of Osters et al 26 The presence of In as the second phase in the In 4 Se 3 matrix of composite samples was confirmed by DSC analysis (Fig. 5), and SEM + EDX observations (Fig.…”