Recently, thermoelectric research for power generation from waste heat has been carried on due to increasing global interest for energy issues. Thermoelectric technology enables direct energy conversion between heat and electricity in a solid-state ma...
Recently, thermoelectric research for power generation from waste heat has been carried on due to increasing global interest for energy issues. Thermoelectric technology enables direct energy conversion between heat and electricity in a solid-state material and its efficiency is governed by the thermoelectric figure of merit, ZT (= S2σT κ-1, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity), much attention has been focused on increasing the performance of the thermoelectric materials.
Specially, substantial make an efforts have been devoted to the research of near-room-temperature(RT) thermoelectric materials for its various applications, however, most research has been focused on Bi2Te3-base compounds. However, Bi2Te3 has the problem of relatively high cost and scarcity of starting materials.
Meanwhile, β-Cu2Se, comprised of low-cost, abundant, and non-toxic elements, has gained much attention recently due to its high ZT at high temperatures. Cu2Se undergoes a phase transition from its low-temperature phase of monoclinic α-Cu2Se (C2/c) to the high-temperature phase of cubic β-Cu2Se (Fm-3m) when the temperature is increased above ~410 K. β-Cu2Se is a superionic conductor with kinetically disordered Cu ions within a face-centered cubic sub-lattice of Se. Liu et al. reported its liquid-like phonon behavior which can lead to extreme suppression of lattice thermal conductivity.
On the other hand, α-Cu2Se is a non-superionic conductor in which Cu atom are localized in the lattice such that the instability issue can be disregarded in this phase. The ZT of α-Cu2Se is less than 0.3 at RT and its low ZT originates mostly from its high hole concentration (~1021 cm-3) due to the easily produced Cu vacancies in this phase.
Frist, we report a new way to control the thermoelectric transport properties of α-Cu2+xSe through over-stoichiometric Cu addition, and we also suggest that Cu-excess α-Cu2Se is a very promising thermoelectric material to replace Bi2Te3 for near-RT applications.
Second, the thermoelectric properties of Cu1.98Se compounds prepared by melt-spinning. Depending on the cooling rate, we could control the microstructure of the melt-spun Cu1.98Se ribbons successfully. The melt-spun ribbons were consolidated by using hot press, and the thermoelectric properties of the compounds were characterized.
Third, we prepared the bulk composites without Cu precipitates even in Cu-excess condition using spark plasma sintering. As well as the enhanced chemical stability, beneficial effects of the interface control on the thermoelectric transport properties of β-Cu2Se were discussed in terms of the role of RGO network. Our results suggest a new direction for developing highly efficient and reliable thermoelectric materials through the interface control using graphene.