Optical and Thermoelectric Properties of Surface-Oxidation Sensitive Layered Zirconium Dichalcogenides ZrS2−xSex (x = 0, 1, 2) Crystals Grown by Chemical Vapor Transport

Abstract

In this work, structure, optical, and thermoelectric properties of layered ZrS2−xSex single crystals with selenium composition of x = 0, 1, and 2 were examined. Single crystals of zirconium dichalcogenides layer compounds were grown by chemical vapor transport method using I2 as the transport agent. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) results indicated that ZrS2−xSex (x = 0, 1, and 2) were crystalized in hexagonal CdI2 structure with one-layer trigonal (1T) stacking type. X-ray photoelectron and energy dispersive X-ray measurements revealed oxidation sensitive behavior of the chalcogenides series. Transmittance and optical absorption showed an indirect optical gap of about 1.78 eV, 1.32 eV, and 1.12 eV for the ZrS2−xSex with x = 0, 1, and 2, respectively. From the result of thermoelectric experiment, ZrSe2 owns the highest figure-of merit (ZT) of ~0.085 among the surface-oxidized ZrS2−xSex series layer crystals at 300 K. The ZT values of the ZrS2−xSex (x = 0, 1, and 2) series also reveal increase with the increase of Se content owing to the increase of carrier concentration and mobility in the highly Se-incorporated zirconium dichalcogenides with surface states.

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

“…The electrical resistivity (ρ) increases with temperature, consistent with the temperature dependence characteristics of semimetals. The room-temperature electrical resistivity of ZrTiSe 4 is four orders of magnitude smaller than TiSe 2 while slightly larger than ZrSe 2 . The sample shows a negative Seebeck coefficient, in agreement with the Hall measurement results.…”

“…The sample shows a negative Seebeck coefficient, in agreement with the Hall measurement results. The magnitude of the Seebeck coefficient increases with temperature, reaching a value of 202 ± 11 μV K –1 at 300 K, which is much larger than the parent compounds. , The Seebeck coefficient and other room-temperature physical properties of ZrTiSe 4 are listed in Table . No obvious bipolar effect was detected in ZrTiSe 4 from the electrical resistivity and the Seebeck coefficient in the temperature range of 2–400 K. The calculated PF (Figure c) shows a maximum value of 0.45 ± 0.05 mW m –1 K –2 at ∼275 K. The room-temperature PF of ZrTiSe 4 is significantly larger than 0.05 mW m –1 K –2 for ZrSe 2 and 3.48 × 10 –4 mW m –1 K –2 for TiSe 2 …”

Transition metal dichalcogenides as catalysts for the hydrogen evolution reaction: The emblematic case of “inert” ZrSe2 as catalyst for electrolyzers

“…The XRD patterns of the samples (Figure 1A) match one of the 1T-ZrSe 2 (ICSD card: 652247), whose CdI 2 layered structure preferentially orients their (001) plane parallel to the substrate. [80][81][82][83] After exfoliation, and in particular after MW treatment, an additional peak emerges at 23.5 • , which may correspond to monoclinic ZrO 2 (space group: P2 1 /c). No XRD peaks attributable to the presence of Ni were observed, indicating the absence of detectable crystalline domains of Ni-based compounds.…”

“…The AFM analysis (Figure 1E and F) indicates that the flakes have a nanometric thickness, fitted by a log-normal distribution peaked at 5.3 nm. Being the c lattice constant of the ZrSe 2 crystal equal to 6.1282 Å, [80][81][82][83] the thickness data indicate the prevalence of few (≤10)layer flakes in the sample. After MW irradiation (MW-ex-ZrSe 2 sample), the exfoliated flakes evolve towards milled irregular nanostructures, some of them resembling zerodimensional quantum dots (Figure 1 G and H).…”

The effect of finite-temperature and anharmonic lattice dynamics on the thermal conductivity of ZrS2 monolayer: self-consistent phonon calculations

“…In this work we study the finite-temperature anharmonic phonons and the associated thermodynamic properties along with the LTC of the two-dimensional (2D) zirconium disulphide (ZrS2) monolayer (ML), which is a typical 2D transition metal dichalcogenide (TMDC) that has been successfully synthesized [32][33][34][35]. Lowering the dimensionality and nano-structuring are reported to play major roles in suppressing the LTC that leads to an enhancement in the figure of merit (ZT) [36][37][38][39][40].…”