Layer-Structured Copper Antimony Chalcogenides (CuSbSe_<i>x</i>S_2–<i>x</i>): Stable Electrode Materials for Supercapacitors

The ever-growing need for energy generation and storage applications demands development of materials with high performance and long-term stability. A sizable number of chalcogenide-based materials have been investigated for supercapacitor applications. Layer-structured chalcogenides are advantageous in terms of providing large surface area with good ionic conductivity and ability to host a variety of atoms or ions between the layers. CuSbS₂ is a ternary layered chalcogenide material that is composed of earth abundant and less-toxic elements. For the first time, we have developed a simple colloidal method for the synthesis of CuSbSe_<i>x</i>S_2–<i>x</i> mesocrystals over the whole composition range (0 ≤ <i>x</i> ≤ 2) by substitution of S with Se. Our approach yields mesocrystals with belt-like morphology for all the compositions. X-ray diffraction results show that substitution of sulfur with selenium in CuSbS₂ enables tuning the width of the interlayer gap between the layers. To investigate the suitability of CuSbSe_<i>x</i>S_2–<i>x</i> mesocrystals for supercapacitor applications, we have carried out electrochemical measurements by cyclic voltammetry and galvanostatic charge–discharge measurements in 3 M KOH, NaOH and LiOH electrolytes. Our investigations reveal that the mesocrystals exhibit promising specific capacitance values with excellent cyclic stability. The unique properties of CuSbSe_<i>x</i>S_2–<i>x</i> mesocrystals make them attractive both for solar energy conversion and energy storage applications

Co_<i>x</i>Cu_1–<i>x</i>Cr₂S₄ Nanocrystals: Synthesis, Magnetism, and Band Structure Calculations

Spin-based transport in semiconductor systems has been proposed as the foundation of a new class of spintronic devices. For the practical realization of such devices, it is important to identify new magnetic systems operating at room temperature that can be readily integrated with standard semiconductors. A promising class of materials for this purpose is magnetic chromium-based chalcogenides that have the spinel structure. Nanocrystals of Co_<i>x</i>Cu_1–<i>x</i>Cr₂S₄ have been synthesized over the entire composition range by a facile solution-based method. While CuCr₂S₄ is a ferromagnetic metal, CoCr₂S₄ is known to be a ferrimagnetic semiconductor. Systematic changes in the lattice parameter, size, and magnetic properties of the nanocrystals are observed with composition. The nanocrystals are magnetic over the entire range, with a decrease in the magnetic transition temperature with increasing Co content. Band structure calculations have been carried out to determine the electronic and magnetic structure as a function of composition. The results suggest that ferrimagnetic alignment of the Co and Cr moments results in a decrease in magnetization with increasing Co concentration