Crystal Structure and Thermoelectric Properties of Layered Van der Waals Semimetal ZrTiSe₄

Abstract

Semiconductors have been studied as the most promising thermoelectric materials for the past decades due to their high Seebeck coefficient. Semimetals usually have a small Seebeck coefficient due to a small difference in the density of states between electrons and holes, compensating each other in the longitudinal direction. However, recent studies suggested that semimetals with large asymmetry between electrons and holes could be good thermoelectric candidates. Here, we report the crystal structure and thermoelectric properties of layered van der Waals semimetal ZrTiSe4. Micrometer-sized single crystals of ZrTiSe4 were obtained by the solid-state reaction. The single-crystal X-ray diffraction study suggests that this material exhibits a trigonal structure with space group P3̅m1 (no. 164), instead of a P2/m (no. 10) monoclinic phase reported in the previous work. ZrTiSe4 has the same crystal structure as ZrSe2 and TiSe2 with Zr and Ti atoms occupying the same site with equal occupancy. Polycrystalline ZrTiSe4 samples consolidated by cold pressing show a semi-metallic type of resistivity in the temperature range of 2–400 K and an n-type conducting behavior. The samples exhibit an unusually large Seebeck coefficient of −202 ± 11 μV K–1 at 300 K, notably higher than the parent phases of ZrSe2 and TiSe2 as well as other semimetals. Based on the first-principles calculations of the electronic band structure, the large Seebeck coefficient of ZrTiSe4 could arise from the conduction band convergence at the M point, resulting in a large density of states (DOS) effective mass for electrons and a highly asymmetric DOS about the chemical potential. Furthermore, owing to a low sound velocity and strong phonon scattering by boundaries and defects, the thermal conductivity exhibits weak temperature dependence and a low value of 2.2 ± 0.4 W m–1 K–1 at 300 K. This work provides useful insights into the crystal structure and thermoelectric properties of semimetal ZrTiSe4.

One-dimensional van der Waals BiSBr: an anisotropic thermoelectric mineral

“…In particular, a substantial improvement in zT (1.9 at 800 K) was reported under the application of 2% biaxial tensile strain. 27 Moreover, several layered van der Waals materials having appreciable zT values, including BiCuOSe, 28 ZrTiSe 4 , 29 and Ta 4 SiTe 4 , 30 have been explored. In this vein, BiSBr has been popular for optoelectronic applications, ascribed to its suitable band gap.…”

First-Principles Investigation of Simultaneous Thermoelectric Power Generation and Active Cooling in a Bifunctional Semimetal ZrSeTe Janus Structure

“…As a result, the out-of-plane direction can show a better thermoelectric power generation performance due to the larger Seebeck coefficient and lower thermal conductivity. Most semimetal systems have a ZT~0.1, but they still hold the potential for specific thermoelectric applications at ambient temperatures with strong directional anisotropy [ 17 ]. This advantage arises from their highly dispersive bands where the major charge carriers significantly outnumber the minor charge carriers [ 13 ].…”

Elucidating the Magnetoelastic Coupling, Pressure-Dependent Magnetic Behavior, and Anomalous Hall Effect in FexTi2S4 Intercalation Sulfides

“…Transition metal chalcogenides have been the subject of numerous studies due to their unique properties and potential interest in the modern high-tech industry, such as transistors, photodetectors, , electroluminescent devices, catalysis, energy conversion, thermoeletric materials, , magnetic refrigeration, and various other electronic devices. , For instance, the thiospinel compounds (Hg,Cd,Fe)­Cr 2 S 4 show coexisting colossal magnetoresistance (MR) and magnetocapacitance effects . Beyond 3D crystal structures, like spinels, perovskites, etc., intercalation metal sulfides M x B 2 S 4 (M, B: transition metals) are attracting much attention for technological applications due to their enhanced electrical properties and richer redox chemistry than the traditional binary metal disulfides ( BS 2 ).…”

“…Transition metal chalcogenides have been the subject of numerous studies due to their unique properties and potential interest in the modern high-tech industry, such as transistors, 1 photodetectors, 2,3 electroluminescent devices, 4 catalysis, 5 energy conversion, 6 thermoeletric materials, 7,8 magnetic refrigeration, 9 and various other electronic devices. 10,11 For instance, the thiospinel compounds (Hg,Cd,Fe)Cr 2 S 4 show coexisting colossal magnetoresistance (MR) and magnetocapacitance effects.…”