The effect of graphene structural integrity on the power factor of tin selenide nanocomposite

Tin selenide graphene nanocomposites (SnSe/GNPs) were fabricated with high-energy ball milling and hot pressing by varying the milling time of graphene. The effect of ball milling time on the graphene integrity and the dispersion homogeneity was investigated and the consequential variation in electrical properties of SnSe/GNPs were analyzed. The evolution of graphene sheets during milling as well as the crystal structure of SnSe/GNPs nanocomposites were systematically studied by X-ray diffraction, Raman analysis, scanning electron microscopy, and transmission electron microscopy. It has been proven that graphene was able to keep its crystallinity at short milling times, but it exhibits agglomeration and poor dispersion within the matrix. However, long milling time has a significant effect on increasing the disorders on graphene structure while it provides well dispersion of graphene. The calculated power factor increases with the addition of graphene and with increasing graphene milling time. The increased power factor is attributed to the homogeneous distribution of graphene, which results in a significant increase in electrical conductivity. At 773 K, the lowest power factor value was reported for the 1-min graphene-milled sample, whereas a 40% enhancement was reported for the 2-h graphene-milled sample. Across a wide temperature range (298-720 K), the 12-h graphene-milled sample shows the best performance owing to the simultaneous increase of electrical conductivity and Seebeck coefficient. These findings indicate the positive effect of milling time on the distribution of graphene, which in turn enables graphene to form a continuous net for carriers to move. This study could provide a greater understanding of the control factors of the mechanical milling process for preparing SnSe/GNPs nanocomposites in order to take full advantage of graphene's extraordinary properties by improving its distribution within the tin-selenide-based composite. (c) 2021 The Author(s). Published by Elsevier B.V. CC_BY_4.0