Enhanced Stability and Thermoelectric Performance in Cu_1.85Se-Based Compounds

Abstract

Liquid-like copper selenium compounds have attracted considerable interest in recent years for their excellent thermoelectric performance, abundant element reserves, and low toxicity. However, the related applications are still limited due to the phase transition and precipitation of Cu under an external field. Here, the cubic Cu1.85Se-based compounds with suppressed phase transition and improved critical voltage (V c) are first studied. In particular, Li/Bi co-doping effectively optimizes hole concentration and the ZTs are substantially improved from 0.2 in Cu1.85Se to 0.7 in Li0.03Cu1.81Bi0.04Se at 760 K. Meanwhile, the latter shows an outstanding V c above 0.22 V at 750 K, which is the highest value in Cu2–x Se thermoelectric compounds to date. Moreover, S is alloyed in Li0.03Cu1.81Bi0.04Se to greatly reduce the thermal conductivity and the ZT is further enhanced to 0.9 for Li0.03Cu1.81Bi0.04Se0.9S0.1 at 760 K. Our work sheds light on a new strategy to realize good stability and enhanced thermoelectric performance, which provides a new direction for further research.

Improved Thermal Stability and Enhanced Thermoelectric Properties of p-Type BaCu2Te2 by Doping of Cl

“…These results are consistent with our previous findings that the dynamic precipitation of Cu occurs during the electrical performance measurements, resulting in a distinct variety of electrical conductivity and Seebeck coefficients. Similar results have been reported in other fast ion conductors, such as Cu 2 Se. , …”

“…where J c is the critical electric current extracted from Figure 6, and L and σ are the effective length and electrical conductivity of the samples, respectively. 35,36 In Figure 6a, the relative resistance increases with the increase of the electrical current before reaching the critical point, attributed to the fact that Cu + in the pristine BaCu 2 Te 2 reoccupies the Cu vacancies during the migration process at a higher current density. This results in the decrease of carrier concentration and the increase of resistance, which reflects the instability of the pristine BaCu 2 Te 2 .…”

“…Similar results have been reported in other fast ion conductors, such as Cu 2 Se. 35,36 Figure 3 shows SEM and EDS images of Cl-doped BaCu 2 Te 2−x Cl x (x = 0.02, 0.04, and 0.06) samples. It can be clearly observed in the SEM images that the second phase with a size of about 10−20 μm exists in all samples with different doping gradients, which is indexed as the enrichment of the Cu and Cl elements and the second phase is the raw material CuCl.…”

“…Total thermal conductivity of the sample can be calculated according to the equation κ tot = DC p ρ. The resistivity, Seebeck coefficient, and power factor of the samples were simultaneously measured on the integrated electrical performance test system ZEM-3 (ULVAC-RIKO), with the test range of 323–823 K. The Hall coefficient ( R H ), the Hall carrier concentration ( p H ), and the Hall mobility (μ H ) were calculated with a Lake Shore 8400 system (Lake Shore Cryotronics, USA) using the four-probe van der Pauw method under a reversible magnetic field of 0.9 T. The critical voltage V c at 550 K was obtained using a modified Netzsch DIL 402C instrument by applying different electric currents for pristine and Cl-doped samples to detect the variation of relative resistance R / R 0 ( R 0 is the sample’s original resistance). − …”

Synergetic Optimization of Electrical and Thermal Transport Properties by Cu Vacancies and Nanopores in Cu2Se

“…Also, the weighted mobility decreases with increasing Cu and In content, indicating that the addition of excess Cu and introducing In atoms not only reduces significantly the carrier concentration but also enhances carrier–carrier scattering to some extent. According to the single parabolic band model, which shows that acoustic phonon scattering is the major scattering mechanism and the scattering factor r is defined as −1/2, the Seebeck coefficient can be described using the Pisarenko relation where represents the decreased Fermi levels, F n (ξ) denotes the n -order Fermi integral, k B is the Boltzmann constant, r is the scattering factor, T is the absolute temperature, e is the electron charge, h is the Planck constant, m * is the density of state effective mass, and n is the carrier concentration. Pisarenko plots at room temperature have also been made with m * = 1 m e , 2 m e , and 3 m e and are shown in Figure f, where m e represents the free electron mass.…”