Rational Design of Cu Vacancies and Antisite Defects for Boosting the Thermoelectric Properties of CuGaTe2-Based Compounds.

CuGaTe2-based compounds show great promise in the application for high-temperature thermoelectric power generation; however, its wide bandgap feature poses a great challenge for enhancing thermoelectric performance via structural defects modulation and doping the system. Herein, it is discovered that the presence of GaCu antisite defects in the CuGaTe2 compound promotes the formation of Cu vacancies, and vice versa, which tends to form the charge-neutral structure defects combination with one GaCu antisite defect and two Cu vacancies. The accumulation of Cu vacancies in the structure of the (Cu2Te)x(Ga2Te3)1-x compounds evolves into twins and stacking faults. This in conjunction with GaCu antisite defects intensify the point defects phonon scattering, yielding a dramatic reduction on lattice thermal conductivity from 6.95 W m-1 K-1 for the pristine CuGaTe2 sample to 2.98 W m-1 K-1 for the (Cu2Te)0.45(Ga2Te3)0.55 sample at room temperature. Furthermore, the high concentration of charge-neutral defects combination narrows the band gap and increases the carrier concentration, leading to an improved power factor of 1.58 mW/mK2 at 600 K for the (Cu2Te)0.49(Ga2Te3)0.51 sample, which is 41% higher than for the pristine CuGaTe2 sample. Consequently, the highest ZT value of 0.82 is achieved at 915 K for Cu0.015(Cu2Te)0.48(Ga2Te3)0.52, which represents an enhancement of about 22% over that of the pristine CuGaTe2 compound.

A Defective Disc-Like Cu1.96S Anode Material with the Efficient Cu Vacancies for High-Performance Sodium-Ion Storage.

Due to their significant capacity and reliable reversibility, transition metal sulphides (TMSs) have received attention as potential anode materials for sodium-ion batteries (SIBs). Nonetheless, a prevalent challenge with TMSs lies in their significant volume expansion and sluggish kinetics, impeding their capacity for rapid and enduring Na+ storage. Herein, a Cu1.96S@NC nanodisc material enriched with copper vacancies is synthesised via a hydrothermal and annealing procedure. Density functional theory (DFT) calculations reveal that the incorporation of copper vacancies significantly boosts electrical conductivity by reducing the energy barrier for ion diffusion, thereby promoting efficient electron/ion transport. Moreover, the presence of copper vacancies creates ample active sites for the integration of sodium ions, streamlines charge transfer, boosts electronic conductivity, and, ultimately, significantly enhances the overall performance of SIBs. This novel anode material, Cu1.96S@NC, demonstrates a reversible capacity of 339 mAh g-1 after 2000 cycles at a rate of 5 A g-1. In addition, it maintains a noteworthy reversible capacity of 314 mAh g-1 with an exceptional capacity retention of 96% even after 2000 cycles at 20 A g-1. The results demonstrate that creating cationic vacancies is a highly effective strategy for engineering anode materials with high capacity and rapid reactivity.