Raman Spectroscopy Study of Phonon Liquid Electron Crystal in Copper Deficient Superionic Thermoelectric Cu_2–xTe

Abstract

Superionic Cu 2-x Te (CT) is an interesting and emerging p-type thermoelectric (TE) material due to the existence of various polymorphic phases and crystal structures, which undergo several structural phase transitions. On the basis of the stoichiometry of the CT compounds, the structure parameters, the carrier concentration (n p ), and the thermal conductivity (κ) can be modulated for optimum TE performance. Further, the understanding of the fundamental properties and their impact on TE parameters is not well understood because of their complex structures. We have investigated the vibrational properties of CT compounds such as Cu 1.25 Te (CT1.25), Cu 1.6 Te (CT1.6), and Cu 2 Te (CT2) using temperature dependent Raman studies in the temperature range of 300−773 K. Several structural phases are probed through remarkably distinct spectra for the CT compounds. The temperature transitions are complex such as (i) eutectic melting into CuTe and Te for both CT1.6 (above ∼593 K) and CT1.25 (above ∼613 K) and (ii) the structural transition from trigonal to orthorhombic and cubic phase for CT2 (above ∼553 K), which are strongly manifested in the Raman study. Further, the role of n p in the Raman spectra has also been investigated. The intensity of the Raman modes (>100 cm −1 ) showed strong n p dependence due to strong plasmon−phonon coupling. The analysis of full width at half-maximum (fwhm) of Raman peaks and qualitative estimation of phonon lifetime (τ i ) showed that CT2 has the minimum lattice thermal conductivity.

Lattice-Matched Metal–Semiconductor Heterointerface in Monolayer Cu2Te

“…Cu 2 Te, a member of group IB transition-metal chalcogenides (TMCs), is known for its applications in thermoelectrics and photovoltaics. − Bulk Cu 2 Te is a typical polymorphic material with several phase transitions, − while its two-dimensional form has been rarely explored. One difficulty hampering the synthesis of Cu 2 Te is that traditional growth methods induce severe Cu deficiency in products, leading to complex nonstoichiometry, Cu 2– x Te. , Recently, Tong et al .…”

Unusual Red Light Emission from Nonmetallic Cu2Te Microdisk for Laser and SERS Applications

“…These peaks are in agreement with the B 3g and B 1 mode frequencies of the main components of the Cu 2 Te phase. [ 35,36 ] According to the Ref. [ 36 ] , the spectra of the samples from Cu 2− x Te with ratios [Cu]/[Te] = 1.5 and 1.75 show an intense peak at 123 cm −1 (B 2g mode), while the one from Cu 2− x Te with [Cu]/[Te] = 2 has a maximum located at 121 cm −1 .…”

“…[ 35,36 ] According to the Ref. [ 36 ] , the spectra of the samples from Cu 2− x Te with ratios [Cu]/[Te] = 1.5 and 1.75 show an intense peak at 123 cm −1 (B 2g mode), while the one from Cu 2− x Te with [Cu]/[Te] = 2 has a maximum located at 121 cm −1 . When 532 nm laser is focused onto the Cu 0.664 Te 0.336 sample with a spot size of ≈1 µm, the Raman characteristics showed good stability with the pronounced B 1 mode peak during the laser intensity increased from 2.5 to 125 kW cm −2 .…”

Study of anisotropic thermal conductivity in textured thermoelectric alloys by Raman spectroscopy

“…Raman mode wise τ values qualitatively estimated from the following eqn (3) , is the reciprocal of FWHM. 31 where Γ is the FWHM of Raman peaks, shown in Fig. 7(a) and (e) .…”