High thermoelectric performance in copper telluride

TLDR: Xun et al. as discussed by the authors used direct annealing without a sintering process to obtain high-density Cu2Te samples and showed that this method can save substantial time and cost during the sample growth.

Abstract: Recently, Cu2-δS and Cu2-δSe were reported to have an ultralow thermal conductivity and high thermoelectric figure of merit zT. Thus, as a member of the copper chalcogenide group, Cu2-δTe is expected to possess superior zTs because Te is less ionic and heavy. However, the zT value is low in the Cu2Te sintered using spark plasma sintering, which is typically used to fabricate high-density bulk samples. In addition, the extra sintering processes may change the samples’ compositions as well as their physical properties, especially for Cu2Te, which has many stable and meta-stable phases as well as weaker ionic bonding between Cu and Te as compared with Cu2S and Cu2Se. In this study, high-density Cu2Te samples were obtained using direct annealing without a sintering process. In the absence of sintering processes, the samples’ compositions could be well controlled, leading to substantially reduced carrier concentrations that are close to the optimal value. The electrical transports were optimized, and the thermal conductivity was considerably reduced. The zT values were significantly improved—to 1.1 at 1000 K—which is nearly 100% improvement. Furthermore, this method saves substantial time and cost during the sample’s growth. The study demonstrates that Cu2-δX (X=S, Se and Te) is the only existing system to show high zTs in the series of compounds composed of three sequential primary group elements. A time-saving procedure for boosting the performance of experimental thermoelectric energy harvesters has been developed by a team in China. Recently, copper sulfide (CuS) and copper selenide (CuSe) compounds have garnered interest as thermoelectric generators because their extraordinarily low thermal conductivities enable highly efficient conversion of temperature swings into electricity. However, copper telluride (CuTe) compounds, which have even lower lattice thermal conductivities than CuS or CuSe compounds, have so far displayed only moderate thermoelectric capacities. Xun Shi at the Chinese Academy of Sciences and co-workers solved this mystery by eliminating the spark plasma sintering procedure normally used to produce high-density CuS and CuSe thermoelectrics. The researchers raised the thermoelectric efficiency by a few times by directly annealing CuTe crystals. They attribute this increase to better control over carrier concentrations in the samples’ crystal structure. Enhanced thermoelectric figure of merit in the fully densified Cu2Te bulk materials by direct annealing method.