Controllable Synthesis of Mesoporous Cu₇Te₄ Flowerlike Structures by Cation-Exchange Method and Their Thermoelectric Properties

Developing reliable synthetic methods for metal telluride micro-nanostructures is essential to achieve a breakthrough in the enhancement of their thermoelectric properties. In this article, a simple and reproducible cation-exchange method to fabricate mesoporous Cu₇Te₄ flowerlike structures by using pre-synthesized β-ZnTe(ethylenediamine)_0.5 (β-ZnTe(en)_0.5) flowerlike templates for thermoelectric applications is proposed. The cation-exchange temperature plays a key role in the formation of products, and the optimal reaction temperature for mesoporous Cu₇Te₄ flowerlike structures is about 135°C. During this process, the Cu ions rapidly occupy the vacancies created by the loss of en-molecules and Zn ions in β-ZnTe(en)_0.5 templates, and the crystal grains grow to mesoporous Cu₇Te₄ flowerlike structures, which are proved by the characterization results of x-ray diffraction, electron microscopy, x-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms. Finally, in thermoelectric measurements, mesoporous Cu₇Te₄ flowerlike structures exhibit higher figure of merit (ZT) than Cu₇Te₄ flowerlike structures without pores due to the improvement of phonon scattering and electrical conductivity.