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.
Thermoelectric (TE) materials have drawn enormous research
interest
for decades as the TE effect facilitates direct conversion of heat
into electrical energy or vice versa, thereby providing an alternative
for power generation/refrigeration. However, the lack of TE materials
that are simultaneously inexpensive, nontoxic, and efficient limits
their industrial utilization. A new approach to address this challenge
could be the electrical functionalization of commercially usednontoxic,
sustainable, lightweight, and low-costthermal superinsulating
materials, e.g., Aerosil200, by doping. In the present work, as a
first step toward this approach, we employ density functional theory
calculations through the Vienna ab initio simulation package to create
and validate a numerical model of pure Aerosil200. This was followed
by the calculation of its electronic structure as well as TE properties
using the BoltzTrap code. The calculated Seebeck coefficient and electrical
conductivity, and thereby the power factor, showed excellent agreement
with the experimentally determined values. Our numerical model, therefore,
paves the way for further improvement of the power factor, hence ZT, through doping of Aerosil200 while retaining its low
thermal conductivity.
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